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Misfire , Again... Fuel Related This Time?


Rocan
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Well, it was nearly a month since I redid my wiring harness for my megajolt and ford EDIS. Things were running really well, and aside from my thermostat being stuck open the car was operating as it should. Two days ago I noticed my temperature gauge started to creep back up, so my thermostat decided to close up again. A leaking hose appeared and last night I had to pull over to fill up some water as temperatures got pretty high into the white zone (I never let it hit red). It was low on coolant, probably from the leak. topped it off. I have new hoses and thermostat on the way, and I think the coolant issue isn't related to my misfire, but it's worth mentioning anyway. 

 

I probably have a slight exhaust header leak as a few nuts are missing, but this miss is far too great for it to be a manifold leak only. I'll button that up today to see if it makes a difference, but it shouldn't as the car has ran just fine in that condition for months. 

 

So here are the symptoms:

 

Car starts perfectly, pretty much instantly every day. It revs freely to redline and displays no symptoms of misfire at all when under no load. When driving, at first all is fine except for a little hesitation to rev up to speed when cold (normal). As the car heats up a bit, the hesitation seems to only be prevalent at high loads and low RPM. When I pass a certain RPM (about 3000, no tach installed right now, I know I know) the car has as much power as it should and it pulls freely. The warmer the engine gets, the more it falls on its face at low RPM. I barely made it home before it started sputtering bad enough to worry me. It's possible its vacuum related (and I have new hoses on order to make sure I fix that), but the only thing to make me think that is my fluctuating idle that I get once in a while (might stay a little high). The main thing that makes me think it is fuel related is that it's really noticeable at very small throttle openings. The Fuel hoses have all been changed, but the filter is probably a few years old and needs changing. If it was fuel starvation I figure it would rear its head in the higher RPMs, but I'm not ruling out a clogged jet + hot engine causing fuel starvation in the lower RPM.

 

 

Ignition system is all NEW and has been gone over about 50 times so I want to rule that out at this point. 

 

Thoughts?

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I have had similar experiences, albeit in a toyota, and it turned out to be an electric fuel pump that overheated.

If you are running the mech pump this would unlikely, as it would rather starve at higher rpm, and not be temp sensitive.

My only other guess would be carb, but I doubt that it would get worse at higher temps, it would be bad from the get go.

Meh, I'm no help today. Lol

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Well. That was simple enough. All four plugs were oil fouled. I've been meaning to change my valve seals for way-too-long now, but have been delaying it because I don't have a shop. I had increased plug gap to .45-.50 because of my megajolt/EDIS, and it would have been fine if it weren't for the oil. I cleaned the plugs and re-gapped to .34... if they still foul I'll go a step colder to help burn it off. It seemed to fix the issue.

 

My thermostat cracked and another hose is leaking; it's a good thing that my new hoses should be here this week. 

 

I need to know, as I've read different things online... What is the definitive answer to this question...

 

Can I replace valve seals without removing the head? I don't see any reason why a lisle valve spring compressor can't get to all the valves. Put a little rope into the cylinder to keep the valves from dropping and I'm golden, no? 

 

http://www.amazon.com/Lisle-16750-Valve-Spring-Compressor/dp/B0009OR96K

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Coupla thoughts....you would want to go to a hotter plug (not colder) if your engine is burning oil.  I'd try that first--my 69 gets about 400mi/qt (223k on the original engine) and runs just fine with one range hotter plug.  Changing plugs are a lot cheaper than even a valve job...and oil is cheaper than engines.

 

If you're gonna do a valve job, do a wet/dry compression test to see how well the rings seal.  You might also do a leakdown test to confirm.  Not much sense in doing a valve job if the rings are weak, as those nice, tight new valves/stem seals will force oil past the rings and you'll probably be back in the same situation you're at now. 

 

cheers

mike

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Thanks mike. Technically speaking i believe a "colder" plug runs hotter... But yes you are correct the idea is to run a step "hotter" to burn off oil. I recently sourced a rebuilt bottom end that I could eventually swap on. I can deal with it burning oil more while accelerating, it's just the deceleration that is hard to avoid (ie off ramp on a highway). Either way ill eventually need to swap valve seals so If it burns, ill just have to deal with it.

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Head has to come off.  the rocker arms and shafts are in the way of any tool.  While you're replacing the seals, check for play in the guides/stems and do a valve job..   if there's corrosion near your water jackets or the PO put in a tii cutting ring gasket have it surfaced as well

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I was the one who installed this head so I know the water jackets are okay, and the gasket is a stock type gasket. I was planning on lapping the valves while the springs are out. I'll definitely be sure to check for play in the guides!

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Chances are if it blows smoke on overrun that valve guides/seals are the problem.  Replacing seals by themselves is a false economy, and is rarely the answer because if they are tired, the guides won't be far behind.  Guides are cheap in the whole scheme of things, and if they are worn you will not get the valve to seal properly at revs, even with a lapping, given you have a rocker putting some sideways thrust on the valvestem as it opens and closes the valve.

 

If the motor is oiling up plugs, chances are it is tired all over. I use NGK 8s(coldish plug) in my race M10 with a schrick 316, but can drive it on the street without fouling plugs.  Even with big output ignition systems I have not found any gains on the dyno with over 32 thou plug gap. I do like the NGK Iridium plugs, being that these are less likely to foul given the fine electrode, and last very well.

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  • 1 month later...

If it cut for a whole second, I would be looking for an electrical problem of the mechanical variety.

As in a lose wire? 

 

Could be my negative lead that goes to the megajolt shaking about (it somehow got pulled out of the molex connector yesterday and I had to mcgyver it back in there. I would notice the tach going dead though if it were that, and that alone shouldn't cause it as it would just cause the ignition to run in EDIS limp home mode. Unless it is the megajolt cycling through a reset after losing power randomly. I suppose it's possible that that is why it's only at low RPM.... hmmmmm. 

 

I'll have to fix that connector and see if it cures it. 

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...sheesh..........that musta been frustrating...

Since the problem began I changed the following:

 

Coil packs, plug wires, spark plugs (twice), EDIS plug, rewired the entire harness, new sensor plug, new shielded wire, new ground cables for the battery and chassis including another ground from cylinder head to passenger fender (I wanted to rule out interference), new alternator, recrimped the +12v ignition line coming off the fusebox, tons of ignition map checking and countless hours of internet searching. 

 

Not counting the heartbreak and fear as the car would studder to a halt randomly and leave me on the side of the road cursing. 

 

Granted, in the long run I'm glad I re-did everything. It is MUCH neater and far more durable now and really needed doing since I was pressed for time the first time around. 

 

 

The most annoying itch is the one you can't scratch. 

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