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Misfire... What could it be?

2K views 13 replies 6 participants last post by  Neilap 
#1 ·
So, a diagnostic thread. my 90' 2300 4plug efi misfires. and symptoms are as followed

When cold engine runs normal, but when coming up to operating temp. it develops a never ending stumbling misfire under 2k rpm and acts like a single cylinder bike engine without enough battery to supply spark past idle.

I checked the ignition module and it is 100% functional. my cars plugs read normal and the exhaust smells that of a lawn-mower after it warms up. ignition is set at 10 d btdc, but I have discovered my camshaft is aligned but its at 4d btdc according to the crankshaft. my plugs are autolite 2524? the copper electrode plugs. my wires, dist cap and rotor are new. my ignition coil is 2 years old. and I have reason to believe that my No.4 cylinder exhaust valve needs replaced or the lifter for said valve. On a timing light as I said my timing was at 10 degrees... without the SPOUT connected. With it connected the computer sets it around 28-32 degrees and when rolling onto the throttle the timing drops and staggers erratically between 4-10 degrees and after near 3k rpm it snaps back to a normal spark curve.

What would you say could be the cause of my warm misfire? Im at a loss of ideas of what could be effected by heat to cause this... Maybe my valvetrain tick is throwing off my knock sensor and causing this?
 
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#2 ·
Does it still have the original pickup coil and/or TFI on the car? The ignition module could be fine when the car is idling and not in use but could be having issues as it warms up while driving.. Ask me how I know... Anyways it goes the same with the pickup coil... Mine did the same thing and then it got worse a few weeks after the small misfires started...
 
#3 ·
I took my module inti advance auto to have it tested and the guy done it enough times to get it really hot and still came out 100% now the pickup sensor in the distributor I bought a new one just incase. I havnt installed it yet pending the fact i need something to knock that pin out to take apart my distributor. I also just tried driving my car with the knock sensor unplugged and it caused my car exhaust to not smell like a lawn mower and my misfires held off a few minutes longer and.. they arent as frequent
 
#5 ·
First pull codes autoparts place may do this or just need a piece of wire and watch check engine flash.
Ps These Fords engine run best on plain cheap Ford plugs. That is what is in my turbo car.
Look at plugs Is any fuel soaked or white. Fuel soaked maybe injector or white no fuel at all. I had a miss in mine and wasn't the ignition but a dead injector.
Pull each plug wire and put spare one in it and lay on metal on engine. Have someone try to start and look if see spark. Have spark on all ignition probably ok.
Now pull one injector connector at a time and see any difference. Car dies try another that one is working, No difference at all you found a dead one either injector or wiring. Need a noid light or just try a injector.
The other thing is a valves or internal. Do a compression test or leakdown test.
Maurice
 
#8 ·
I changed my fuel filter a couple weeks ago and.. it actually caused most of my symptoms oddly enough. All my plugs are uniform light tan to with small amounts of white build up on the outside of the outer electrode (you can wipe it off with a finger) also my plugs smell of absolutely nothing and are gapped to .044. And I do know i have a bad exhaust valve, i can hear the thing clatter through the exhaust but this misfire seems to be random on any cylinder it so chooses. And the miss fires really act up primarily after you accelerate, coast and roll onto the gas again it will sputter on pretty much all cylinders for usually 3 seconds then goes back to acceleration. This is overcame how ever by a long enough period of time coasting before accelerating again. Also it Never misfires while revving the engine out of gear. It sounds like angles apart from the valvetrain what ever issue. Come daylight im testing my fuel pressure regulator as i removed the vacuum line and smelled gas residue but no present gas. Im going to see about temporarily blocking off my EGR to see if that makes a difference etc. And on a note of changing the fuel filter, the gas that camw out of the lines was clear but obviously the bad filter poured out dark whiskey brown gas from the inlet side. It has no markings on it so i suspect it is from 1989. The before and after changing the filter was normal rpm function and lack of power to full power and like im flooding the engine. Also the RPMs hang and drop much much slower now.
 
#9 ·
I'll be curious to know what the fuel pressure looks like. From what you're saying, it looks like you've changed everything in the ignition system and the plugs show good color, idle stability is good. From what you're saying, the issue occurs under load. It's sounding like a lean misfire. Assuming that you have adequate fuel pressure, you might also want to look for vacuum leaks. It's possible you have a bad injector as well. So your car is a speed density car for sure?
 
#10 ·
Yep. No MAF or a connector for it. The car also from previous owner has a homebrew cold air intake, the ac, smog control and cat are deleted. But i do mention that these problems only occur once the temp guage hits normal range. Before that it runs perfectly fine except rich smelling exhaust. I just now bought a o2 sensor cause the one on it came with the car in 89 and... lo and behold my header is cast in a way that any 22mm o2 socket or wrench has thin enough walls to fit over the nut to take it off.
 
#11 ·
pull codes like maurice said, but have you checked your o2 sensor? when one of mine was going bad it had me fooled at first by thinking i had a misfire for the first few days.
 
#12 · (Edited)
Im actually trying to Hah. I bought a new one but my header dont let me clear a socket onto it. the o2 is the original one from '89 with 175k miles. I also hit it with a hammer... hard quite a few times... its dead as a doorknob, Edit - my codes, Errr my check engine light bulb is blown and I dont have a analog voltmeter with a 25DC setting to pull them >_<
 

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#14 ·
I dont, i would have to order one. I live in west virginia, if you need something no one will sell it. And before i go change that bulb il need to get another gauge cover thing that the light switches plug into. Half the clips are broke and if i move it il break the rest off. This car is a prime example of uncared for. Hence why i got it so cheap around here with virtually no rust
 
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