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rough engine intermittent
TIA to all.
1978 Chrysler 318 V-8 gasoline engine, www.ctow.ca/Trojan26, hour-meter coming up to 1000 hours, about half of them in the four years I've owned the boat. Recently the engine began to run rough, stumbling quite badly. This happened several times about twenty minutes out of port, trolling along in the 1200-1400 rpm range. Twice, I have then put the boat up on plane to scoot home (3200-3400 rpm), only to find that half-way home the whole problem disappears quite suddenly and dramatically, the engine smooths out, revs pick up and I have to pull back on the throttle. One other observation: when misbehaving the port exhaust manifold (I think - the thing with the risers leading to exhaust hoses, muffler...) stays cold. Once the problem clears up, both manifolds get warm. My mechanic found that some of the exhaust manifold plugs had corroded out, so he retapped and replaced them, cleaning up the engine compartment air (dangerous to be exhausting CO into engine room, I know), and he said that likely explained my problem: that after a while the engine area filled with exhaust which didn't support combustion well enough. Running on plane scooped more fresh air in through the vents and so it cleared up. (Didn't explain the cool port manifold however...) The engine did sound much better with the plugs replaced, but the stumbling after twenty minutes of low-speed operation recurred. I checked both the water-separating and inline fuel filters, and found a trace of sediment in the water-separating one, but no water. I cleaned the air filter, and brightened and tightened the battery connections. The mechanic checked the distributor by feeling for shocks, but got none. Of course, when I took him out to demonstrate the problem, it didn't occur, although we went right upon plane rather than reproducing the experimental conditions exactly. So, yesterday I changed the spark plugs (reminding me yet again of the joys of standing on my head for hours in a tiny space in the bilge). The old ones were blackened, and I checked a few gaps but didn't really dwell on this (no pun) and they seemed OK. The new plugs were in the 0.032" range. The old ones, especially at the aft end of the engine which sits lower due to the engine not being level in the boat (straight-shaft inboard), were oily on the threads, and I think that the further aft one had oil further into the block on the threads ... which seems strange to me. They're very hard to get at with a spark plug wrench, and I'm wondering if they were never quite tightened in enough. (I was careful not to overtighten, however - having stripped threads once many years ago...) I was going to change the leads, too, just for thoroughness, but couldn't find the right marine set late on a Saturday afternoon. Will have another look Monday. The distributor cap and electronics control module were new two summers ago (about 200 engine hours ago), as were the plugs and leads. Then, I took the boat out for a prolonged low-speed cruise - and everything worked perfectly. The weather was a bit cooler than it has been here (26C instead of 32C) and a bit windier, so again my original conditions could not be exactly replicated, but I'm hoping the problem had something to do with the plugs. Summary: was running rough after twenty minutes of low-speed operation, port exhaust manifold cool, cleared up after a few minutes at planing speed. Anything obvious that I'm missing? Thanks again. Charles ==== Charles T. Low www.boatdocking.com ==== |
Last season I had a problem with either the carb float sticking and/or the
needle valve sometimes not seating causing excess fuel to "dribble" into the engine causing the symptoms you describe. I would then have to coax the revs up and at the higher speed, that extra fuel was not a problem, and the problem would resolve itself. I was not that anxious to replace the float/needle valve last season so thought I'd try something different. I installed a fuel shut off, and ran the carb dry before storing (I removed the plugs and sprayed the fogging oil directly into the cylinders and cranked over a few times). This spring before firing it up, I sprayed carb cleaner into the carb fuel bowl via the vent and let it sit for 5 minutes ... then started it up. So far no problems, so here's hoping I won't have to work on the carburator at all. Something I heard you might try, is install the fuel shut off (if you don't already have one), and if it starts missing, shut off the fuel and run the carb dry. Then tap on the carb (to free a stuck float/needle valve and gently), then turn on the fuel and see if the problem is gone. I have a mechanical fuel pump ... maybe if you have an electric pump, just pull the fuse??? And if the problem goes, then I guess the decision would be to repair the carb ... or not. Recently the engine began to run rough, stumbling quite badly. This happened several times about twenty minutes out of port, trolling along in the 1200-1400 rpm range. Twice, I have then put the boat up on plane to scoot home (3200-3400 rpm), only to find that half-way home the whole problem disappears quite suddenly and dramatically, the engine smooths out, revs pick up and I have to pull back on the throttle. |
15 years ago I had a 55 hp evinrude that ran very rough . Repair shop
did a tune up but could not find anything amiss. Next time out same thing happened. Once up on plane , hitting wave tops , engine began missing and stumbling. By accident I jiggled ignition key , found it was loose. Turned out ignition switch was making/breaking in rough water. First thing I check now on every trip out. Keith in BC |
I'll remember that one
Turned out ignition switch was making/breaking in rough water. First thing I check now on every trip out. Keith in BC |
Thanks, Mike,
So far, I replaced the spark plugs and since then have had no trouble. That doesn't mean the trouble is over, but preliminary indications are good. The electrodes or whatever they're called were black, and there was oil on the screw threads, moreso the further aft on the engine (which sits a bit lower than the front) ... what this means I have no idea and so far no one else I've asked does either. I checked a few of the gaps and they seemed about the same as on the new plugs, around 0.032". I'm also going to replace the leads just for thoroughness. The engine was compression-checked four years ago, about 500 hours of running time, so a lot might have changed since then. But, although it uses oil, it doesn't use much. I put in a litre only every 50 hours or so (which is about when I should be changing it anyway). Thanks again. Charles ==== Charles T. Low www.boatdocking.com ==== "Mike G" wrote in message ews.com... A couple of things come to mind but the top of the list one is that you are running rich and loading up the engine at the low RPM and the good run at WOT is cleaning things up. A compression check probably wouldn't be out of order either since the second item on the list is a question of how well the valves are seating. Especially if you do a lot of trolling. five hundred hours of more low RPM trolling then high speed operation can give you quite a build up of carbon which may be getting to a point where the seating is only marginal. There is always the hotter plug thing but since I'd only consider it if you were doing a whole lot more trolling then running at WOT. I'd only suggest it after you gave things a lot of thought and a second opinion from your mechanic. I know it doesn't address the manifold thing but................. Good luck -- Mike G. Heirloom Woods www.heirloom-woods.net |
Thanks. The carb remains a source of mystery to me, although I've read about
how they work and looked at diagrams - I think I need to see it disassembled in front of me and be talked through it once. I have thought of a carburetor problem. I do have a fuel shut-off. Anyway, it's working at the moment, but I'll have to give this some more thought, because reliability is so important. My mechanic didn't mention the carbutetor, but I also didn't ask him. I think it's more likely something affecting only some cylinders, because of the coolness of one manifold while the problem is active, resolving as the problem disappears. Charles ==== Charles T. Low www.boatdocking.com ==== "Bowgus" wrote in message ... Last season I had a problem with either the carb float sticking and/or the needle valve sometimes not seating causing excess fuel to "dribble" into the engine causing the symptoms you describe. I would then have to coax the revs up and at the higher speed, that extra fuel was not a problem, and the problem would resolve itself. I was not that anxious to replace the float/needle valve last season so thought I'd try something different. I installed a fuel shut off, and ran the carb dry before storing (I removed the plugs and sprayed the fogging oil directly into the cylinders and cranked over a few times). This spring before firing it up, I sprayed carb cleaner into the carb fuel bowl via the vent and let it sit for 5 minutes ... then started it up. So far no problems, so here's hoping I won't have to work on the carburator at all. Something I heard you might try, is install the fuel shut off (if you don't already have one), and if it starts missing, shut off the fuel and run the carb dry. Then tap on the carb (to free a stuck float/needle valve and gently), then turn on the fuel and see if the problem is gone. I have a mechanical fuel pump ... maybe if you have an electric pump, just pull the fuse??? And if the problem goes, then I guess the decision would be to repair the carb ... or not. Recently the engine began to run rough, stumbling quite badly. This happened several times about twenty minutes out of port, trolling along in the 1200-1400 rpm range. Twice, I have then put the boat up on plane to scoot home (3200-3400 rpm), only to find that half-way home the whole problem disappears quite suddenly and dramatically, the engine smooths out, revs pick up and I have to pull back on the throttle. |
OT but may be worth sharing: And something else I once heard ... spark plugs
are subject to vibration, and the ceramic insulation may crack over time, resulting in carbon tracking and reduction/loss of ignition spark. To sum up, the story is that plugs may look good, but may in fact not be. So replacing then every couple of seasons is I'm thinking not a bad idea ... I think I'll include bi-annual plug replacement in my preventive maintenace. I think it's more likely something affecting only some cylinders, because of the coolness of one manifold while the problem is active, resolving as the problem disappears. In my V6, there's a ball/spring mechanism in the cooling system that I come across every fall when I pull all the water lines for draining/winter storeage. I've just now looked through my Seloc manual, and don't see it. It may have something to do with controlling water flow to each manifold ... dunno ... I'll keep looking for info on that. If one manifold is cold, that says to me that's where (most of) the water flow is going. And it could be you have 2 problems. Perhaps you had/have some water in your fuel/tank ... gas line antifreeze (alcohol) would absorb any water allowing it to pass through the system. Gas treaments apparently also absorb water. One reason I picked a carburated engine is that they're much more resistant to water in the fuel ... may stumble a bit, but the water tends to make it's way through the carb eventually ... unlike an injected system which I understand may have to be torn down to get the water out. So, a water separator is a "shall" for injected systems. |
Charles T. Low wrote:
So far, I replaced the spark plugs and since then have had no trouble. That doesn't mean the trouble is over, but preliminary indications are good. The electrodes or whatever they're called were black, and there was oil on the screw threads, moreso the further aft on the engine (which sits a bit lower than the front) ... what this means I have no idea and so far no one else I've asked does either. And this is an interesting point. Taken together with your consumption, it could be sucking oil from the guides on start/warmup that's sat in the head (proportionately moreso aft), and eventually fouling the plugs. Have you checked for any smoking at startup? You could also pull your new aftmost plug after a brief startup/shutdown to see if it's likewise getting oily. If it were the case the problem would resurface after awhile & let you know. Nice book, BTW. |
Thanks and to the several others who have offered recent help.
And although I had hoped the problem was fixed, it recurred yesterday. As soon as it started to stumble, after trolling around for a while (teaching my daughter how to dock!), I took her up on plane and the whole thing straightened out in very short order. Very weird. I haven't quite got the innards of an engine visualized to the extent that I can see how guides and spark plugs inter-relate, but no matter - all food for thought, research, and further discussion with my mechanic. Thanks again. Charles P.S. And thanks for the kind words. ==== Charles T. Low www.boatdocking.com ==== wrote in message oups.com... Charles T. Low wrote: So far, I replaced the spark plugs and since then have had no trouble. That doesn't mean the trouble is over, but preliminary indications are good. The electrodes or whatever they're called were black, and there was oil on the screw threads, moreso the further aft on the engine (which sits a bit lower than the front) ... what this means I have no idea and so far no one else I've asked does either. And this is an interesting point. Taken together with your consumption, it could be sucking oil from the guides on start/warmup that's sat in the head (proportionately moreso aft), and eventually fouling the plugs. Have you checked for any smoking at startup? You could also pull your new aftmost plug after a brief startup/shutdown to see if it's likewise getting oily. If it were the case the problem would resurface after awhile & let you know. Nice book, BTW. |
About that ball/spring thing ... it's function is still not clear to me, but
.... it's purpose seems to be to balance the cold water bypass to the 2 sides of the (e.g. my V6) engine. There's a pic of it ... it's at the top of the lower (bottom) diagram ... Warm Manifold System. So if one manifold is cold, maybe the thermostat is not opening as soon as it should (engine is actually overheating) and cold water is being directed more to one manifold (by the tee valve assembly) rather than to both? The link ... http://www.perfprotech.com/home/tech...oling-tips.htm Hey, just thinking out loud here :-) In my V6, there's a ball/spring mechanism in the cooling system that I come across every fall when I pull all the water lines for draining/winter storeage. I've just now looked through my Seloc manual, and don't see it. It may have something to do with controlling water flow to each manifold ... |
I had a little look at that link and am having trouble following the
description - not the type of thing to read in a quick scan! In the meantime, the engine is still intermittently running rough (when run at low speed on hot days for 20-30 minutes, clears up in a few minutes under higher load...). I have found corrosion inside the distributor cap and will be replacing that, then reassessing - the number of possible causes that I have come up with is a little staggering - and my mechanic agrees! I also favour having a look inside the carburetor, but mechanic is hesitant, saying they're often never the same after, in his experience ... hmm... ==== Charles T. Low www.boatdocking.com ==== "Bowgus" wrote in message ... About that ball/spring thing ... it's function is still not clear to me, but ... it's purpose seems to be to balance the cold water bypass to the 2 sides of the (e.g. my V6) engine. There's a pic of it ... it's at the top of the lower (bottom) diagram ... Warm Manifold System. So if one manifold is cold, maybe the thermostat is not opening as soon as it should (engine is actually overheating) and cold water is being directed more to one manifold (by the tee valve assembly) rather than to both? The link ... http://www.perfprotech.com/home/tech...oling-tips.htm Hey, just thinking out loud here :-) |
Charles T. Low wrote:
I had a little look at that link and am having trouble following the description - not the type of thing to read in a quick scan! In the meantime, the engine is still intermittently running rough (when run at low speed on hot days for 20-30 minutes, clears up in a few minutes under higher load...). I have found corrosion inside the distributor cap and will be replacing that, then reassessing - the number of possible causes that I have come up with is a little staggering - and my mechanic agrees! I also favour having a look inside the carburetor, but mechanic is hesitant, saying they're often never the same after, in his experience ... hmm... ==== Charles T. Low www.boatdocking.com One should expect it to be somewhat better, and in no qualified hands, ever the worse for care. My old zenith carb was worn so bad that the throttle shaft rattled on idle, its' fibre end washers worn way out, delivering varying amounts of vacuum leak into the intake manifold, which really made life with the old girl an erratic thing, to say the least, particularly when lower power settings were needed. As well, a somewhat sticky needle valve must have been able to stick either open or closed, mysteriously and capreciously. It's better, now. Fixing a carburettor is an essential basic automotive and boating skill which, thanks to induction fuel injection and computerised engine control, is becoming a skill of the past. If your mech is dubious, you need a real mech. A couple of small rubber "O" rings on the ends of the shaft, retained with a little brass snare wire seems to have steadied the engine up considerable. Trry K ==== "Bowgus" wrote in message ... About that ball/spring thing ... it's function is still not clear to me, but ... it's purpose seems to be to balance the cold water bypass to the 2 sides of the (e.g. my V6) engine. There's a pic of it ... it's at the top of the lower (bottom) diagram ... Warm Manifold System. So if one manifold is cold, maybe the thermostat is not opening as soon as it should (engine is actually overheating) and cold water is being directed more to one manifold (by the tee valve assembly) rather than to both? The link ... http://www.perfprotech.com/home/tech...oling-tips.htm Hey, just thinking out loud here :-) |
Thanks, Terry,
A marine mechanic to me is a bit like a hairdresser to my wife - we have a relationship, and I feel loyal. That might interfere with getting my carb maintained, however, and I'll have to think about how to approach that. I'll come up with something. Step number one will be to replace my distributor cap, rotor and leads (they have to be specially ordered - old engine, 1978...) and then reassess. ==== Charles T. Low www.boatdocking.com ==== "Terry Spragg" wrote in message ... One should expect it to be somewhat better, and in no qualified hands, ever the worse for care. My old zenith carb was worn so bad that the throttle shaft rattled on idle, its' fibre end washers worn way out, delivering varying amounts of vacuum leak into the intake manifold, which really made life with the old girl an erratic thing, to say the least, particularly when lower power settings were needed. As well, a somewhat sticky needle valve must have been able to stick either open or closed, mysteriously and capreciously. It's better, now. Fixing a carburettor is an essential basic automotive and boating skill which, thanks to induction fuel injection and computerised engine control, is becoming a skill of the past. If your mech is dubious, you need a real mech. A couple of small rubber "O" rings on the ends of the shaft, retained with a little brass snare wire seems to have steadied the engine up considerable. Trry K |
Hi Charles,
I once owned a 1977 GMC van with a 350 carbureted engine. I bought it (ab)used and it used 1 quart of oil for 500 miles, I started using 20W-50 oil as the back plugs would foul with oil in the course of about 5000 miles, and I would have to pull them and clean them. It also would run rough if it was idled too much and would clear up once out on the highway. I pulled the valve covers and found oil sitting there. The problem was the oil drain holes in the head were plugged and the oil was going down the valve stems into the piston chambers. I plunged out the holes with a coat hanger and the entire problem went away. I then got over 2000 miles to a quart of 10W-30 and the plugs never fouled again. On this same vehicle I installed a GM professionally rebuilt carburetor and then immediately had to have it repaired/rebuilt by a local small engine place, who put the proper Power valve spring in. FWIW. Kevin Charles T. Low wrote: Thanks, Terry, A marine mechanic to me is a bit like a hairdresser to my wife - we have a relationship, and I feel loyal. That might interfere with getting my carb maintained, however, and I'll have to think about how to approach that. I'll come up with something. Step number one will be to replace my distributor cap, rotor and leads (they have to be specially ordered - old engine, 1978...) and then reassess. ==== Charles T. Low www.boatdocking.com ==== "Terry Spragg" wrote in message ... One should expect it to be somewhat better, and in no qualified hands, ever the worse for care. My old zenith carb was worn so bad that the throttle shaft rattled on idle, its' fibre end washers worn way out, delivering varying amounts of vacuum leak into the intake manifold, which really made life with the old girl an erratic thing, to say the least, particularly when lower power settings were needed. As well, a somewhat sticky needle valve must have been able to stick either open or closed, mysteriously and capreciously. It's better, now. Fixing a carburettor is an essential basic automotive and boating skill which, thanks to induction fuel injection and computerised engine control, is becoming a skill of the past. If your mech is dubious, you need a real mech. A couple of small rubber "O" rings on the ends of the shaft, retained with a little brass snare wire seems to have steadied the engine up considerable. Trry K |
Thanks, Kevin,
I'm considering having the carb rebuilt, but have been warned that sometimes it ends up worse, even in experienced hands - or that such bad damage is found inside that it can't be salvaged. Something like what you're suggesting makes sense ... I just have never personally looked into the guts of an engine enough to know quite exactly what you mean. But is the kind of thing you're suggesting something for mechanic, or could anybody do it? It seems to me that unbolting the covers and having a look wouldn't be beyond the average person's capability. Then you would need a gasket kit to put it all back together? Charles ==== Charles T. Low www.boatdocking.com ==== "Kevin & Debbie" wrote in message ... Hi Charles, I once owned a 1977 GMC van with a 350 carbureted engine. I bought it (ab)used and it used 1 quart of oil for 500 miles, I started using 20W-50 oil as the back plugs would foul with oil in the course of about 5000 miles, and I would have to pull them and clean them. It also would run rough if it was idled too much and would clear up once out on the highway. I pulled the valve covers and found oil sitting there. The problem was the oil drain holes in the head were plugged and the oil was going down the valve stems into the piston chambers. I plunged out the holes with a coat hanger and the entire problem went away. I then got over 2000 miles to a quart of 10W-30 and the plugs never fouled again. On this same vehicle I installed a GM professionally rebuilt carburetor and then immediately had to have it repaired/rebuilt by a local small engine place, who put the proper Power valve spring in. FWIW. Kevin |
Hi Charles
The actual R & R of the valve covers was easy enough and the cleaning of the drain holes was a no brainer, but to get at the covers to take them off my boat engines would be a rather large undertaking. The van engine wasn't too bad. I have no idea if you can still buy brand new carburetors or not, it may be an option. I had considered buying a brand new Holley back in 1980 but decided to go with the "Factory Fresh GM Rebuilt", which was junk. Apparently the most noticeable symptom of plugged drain holes was the puff of blue smoke that would come out of the exhaust pipe when I started the Van after it had sat for a while. I don't think I could see that on my I/O's but you might on your inboard. Just guessing. I would mention my experience to your mechanic to get his opinion. Good luck and have a great long weekend. Kevin Charles T. Low wrote: Thanks, Kevin, I'm considering having the carb rebuilt, but have been warned that sometimes it ends up worse, even in experienced hands - or that such bad damage is found inside that it can't be salvaged. Something like what you're suggesting makes sense ... I just have never personally looked into the guts of an engine enough to know quite exactly what you mean. But is the kind of thing you're suggesting something for mechanic, or could anybody do it? It seems to me that unbolting the covers and having a look wouldn't be beyond the average person's capability. Then you would need a gasket kit to put it all back together? Charles ==== Charles T. Low www.boatdocking.com ==== "Kevin & Debbie" wrote in message ... Hi Charles, I once owned a 1977 GMC van with a 350 carbureted engine. I bought it (ab)used and it used 1 quart of oil for 500 miles, I started using 20W-50 oil as the back plugs would foul with oil in the course of about 5000 miles, and I would have to pull them and clean them. It also would run rough if it was idled too much and would clear up once out on the highway. I pulled the valve covers and found oil sitting there. The problem was the oil drain holes in the head were plugged and the oil was going down the valve stems into the piston chambers. I plunged out the holes with a coat hanger and the entire problem went away. I then got over 2000 miles to a quart of 10W-30 and the plugs never fouled again. On this same vehicle I installed a GM professionally rebuilt carburetor and then immediately had to have it repaired/rebuilt by a local small engine place, who put the proper Power valve spring in. FWIW. Kevin |
Thanks, Kevin,
I am certainly saving this information for future use. In the meantime, however, I discussed rebuilding the carburetor with an engine rebuilder, and he interrogated me at length about my problem and found it very puzzling. He did say, however, that a simple explanation could be the richness or idle adjustment screws on the carb being out of whack (I having been advised elsewhere "not to go near that carb!"). I backed these two screws out a bit more (double-barreled carb) and the thing _seems_ to be working normally again! There's also an idle-adjustment screw on the actual shift-cable linkage, but I'm talking about a spring-screw(s) lower down on the carburetor itself. If it continues along like this, I'll perhaps still have the carb looked at over the winter, but for the moment I don't want to tamper with success. Wish me luck! Charles ==== Charles T. Low www.boatdocking.com ==== "Kevin & Debbie" wrote in message ... Hi Charles The actual R & R of the valve covers was easy enough and the cleaning of the drain holes was a no brainer, but to get at the covers to take them off my boat engines would be a rather large undertaking. The van engine wasn't too bad. I have no idea if you can still buy brand new carburetors or not, it may be an option. I had considered buying a brand new Holley back in 1980 but decided to go with the "Factory Fresh GM Rebuilt", which was junk. Apparently the most noticeable symptom of plugged drain holes was the puff of blue smoke that would come out of the exhaust pipe when I started the Van after it had sat for a while. I don't think I could see that on my I/O's but you might on your inboard. Just guessing. I would mention my experience to your mechanic to get his opinion. Good luck and have a great long weekend. Kevin |
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