Intermittent misfire on 7.3

DowneyB

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I have a 7.3 that kinda "popped" one morning when I started it to leave for work, and its had a very subtle miss since then. I've had this motor for years and it is kinda worn out but its always ran without a hiccup until now. It does use a fair amount of oil.

The miss is almost imperceptible at idle, it is most obvious when loading it at around 2000 - 2500 rpm, and it usually misses but occasionally it will run smooth for a few revolutions. At idle it will occasionally shoot a hard fire out of the exhaust. Oh it has started producing this very visible white haze/smoke when idling cold. The haze almost disappears when warmed up but it is still there. I'm sure the neighbors love the diagnostic sessions I've had lately.

I took the valve covers off and could find nothing loose or out of place. I ran it without them and everything moved like it should with no odd noises or escaping gasses.

I just did a compression test last night, all cylinders measured right around 280 psi except #7, which came in at 190 consistently. I'm pretty sure the adapter I had did not seat/seal in the glow plug hole, but otherwise it worked okay. The #5 glow plug was wet/oily when I took it out. I did idle the truck for a few minutes so that the engine wasn't stone cold for the compression test. It does smoke a bit if you take the oil cap off while running.

This is not a truck I have spent a lot of money on, mostly because I can't afford to spend a lot on it. I've had the motor for almost 20 years, it was in my first truck and then sat for most of the last 5 years until last January. I put a used IP on it a long time ago, but I have never touched the injectors. I have an electric fuel pump on it, and I have to keep cleaning the rust flakes out of the prefilter or the pump will start sucking air from a fitting somewhere.

Does this sound like an injector could be causing this? It will be a bit until I can afford a set but I also don't want to throw money at it if I don't have to. Is there something obvious that I should check for or might be missing? I ran a filter full of ATF through it, but it didn't seem to help much. I haven't really driven it since then as I don't know if it will do more damage or not.
 

Nero

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How many miles are on it? Injectors could be worn, but that low compression is unsettling.
 

Austin86250

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if atf isnt helping either your injectors are too far gone to save or it has to do with your low compression it should be mid 300's to low 400's and should be very close to each other within 20 psi or so if you really do suspect it didn't seal right try some teflon next time, but the white haze when cold is most likely injectors
and like nero said how many miles? when they get up there in miles the realm of possibilities opens up
 

Nero

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Yeah white haze at idle is definitely tired injectors. I put a used set in my in laws idi, at 223k miles, it cleared it right up.
 

IDIBRONCO

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Yeah white haze at idle is definitely tired injectors.
Or it's the timing. DowneyB, did you have the timing set when you put the used pump on? The white haze/smoke at idle, especially while cold, makes me think timing first.
 

DowneyB

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I'll be honest, I have no idea how many miles are on this engine. Its a 1990 7.3 (I think) and I've put probably at least 80k on it since I've owned it. It was in an '86 f250 I bought when I was 17 (around 2003 or so), and when that truck fell apart I took it out (like 5 years ago) and put it in a marginally better '86 f250 that was... cheap. I first started it in the second truck last fall, hung a plow on it New Years Eve, and when my grand marquis died in April I started driving it every day until this.

I did a compression test years ago and they were all closer to the upper 300s if I remember correctly. They were all 270 to 290 this time except for the one. That one cylinder is my biggest hesitation to spending a lot of money on injectors at the moment.

Its always smoked just a little since I started driving it again, but nothing like this. My biggest question is if it will hurt it to drive with a bad injector? Can I keep driving it for now, and dose it with ATF (or if there is something better) and see what happens?
 

IDIBRONCO

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My biggest question is if it will hurt it to drive with a bad injector?
That would depend on what the bad injector is doing. If it's hanging wide open and dumping too much fuel into the cylinder, then it could hurt the engine to drive it a lot. You could end up washing all of the oil off of the cylinder walls and scoring the cylinder.
Can I keep driving it for now, and dose it with ATF (or if there is something better) and see what happens?
I would certainly try it. Atf works pretty well. I prefer Hot Shot's Diesel Extreme myself.
 

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