M10 miss firing issue HELP

[Dawskip]

My m10 died in me a few weeks ago, was idling and shut off. I replaced the fuel pump with a walbro 255 I had laying around, removed the inline pump with that so that was my main pump. Started up, made it down the street and it died again.

i got it back home, replaced the fuel filter, spark plugs, spark plug wires, cap and rotor. The car now starts up but has a bad miss and will not stay running unless I’m giving it some gas.

I should add that when I took spark plug #4 out it had a lot of oil on it.

how should I diagnose this? Is this fixable?

[Sunnyledge]

Can you provide a video with audio of the engine start up and running/misfiring?

[twright]

Check the compression of all four cylinders. You need to know if its OK before you spend a bunch of money on fuel and ignition stuff.

[Sunnyledge]

Was this condition gradual in onset, increasing over weeks/months, or rapid in onset? You obviously have some spark and some fuel. The M10 is really sensitive to vacuum leaks, causing stumbling idle with the engine running better at higher rpm’s. Most of these leaks occur from breaks in tubing which can be hard to see. Going through the distributor/wires/plugs should eliminate it as an issue, but always reassuring to put a timing light on each spark plug wire to see if it is getting a spark. Harder to tell if each injector is properly operating. I didn’t understand your comment about the fuel pump. Are you still running both an in tank and an in line fuel pump?

[Dawskip]

Was this condition gradual in onset, increasing over weeks/months, or rapid in onset? You obviously have some spark and some fuel. The M10 is really sensitive to vacuum leaks, causing stumbling idle with the engine running better at higher rpm’s. Most of these leaks occur from breaks in tubing which can be hard to see. Going through the distributor/wires/plugs should eliminate it as an issue, but always reassuring to put a timing light on each spark plug wire to see if it is getting a spark. Harder to tell if each injector is properly operating. I didn’t understand your comment about the fuel pump. Are you still running both an in tank and an in line fuel pump?

I’ve had some issues with it missing or running a little poor until it got warm, but never any no start symptoms really. I will get a video ASAP to show what’s going on, but to clarify about the fuel pump — I took the in tank out, installed the 255 there, removed the inline pump.

edit: I know my exhaust manifold leaks due to the previous owner(s) breaking off one of the exhaust studs in the head, could that really be the reason it won’t run though?

[Dawskip]

Check the compression of all four cylinders. You need to know if its OK before you spend a bunch of money on fuel and ignition stuff.

4 - 170

3 - 165

2 - 170

1 - 175

[Dawskip]

Also discovered my oil pan gasket (upper pan) definitely needs to be replaced as it’s leaking, but again, I don’t think this would be the cause of the no start would it?

[Sunnyledge]

Those are ok compression numbers. Exhaust manifold leak doesn’t affect starting. Leaky oil pan doesn’t affect start up unless you are so low on oil that your engine is about to seize. Not likely if you weren’t getting an oil pressure light.

[Dawskip]

Those are ok compression numbers. Exhaust manifold leak doesn’t affect starting. Leaky oil pan doesn’t affect start up unless you are so low on oil that your engine is about to seize. Not likely if you weren’t getting an oil pressure light.

Yeah I know I’m topped up on oil, checked it before and after I initially trie starting it up.

I did notice that if I rev it, form the 4-5k range it seemed to smooth out and sound normal, maybe a vacuum leak?

looked around the houses and all seem to be fine, unless it’s a intake manifold gasket that’s gone.

[Sunnyledge]

Unlikely an intake manifold gasket. Usually a hose. When I decided to replace all my 35 year old hoses I found 3 cracks/breaks in the large vacuum hose that goes from the idle valve into the plastic boot on the throttle body that I didn’t know/couldn’t see.

[Dawskip]

Unlikely an intake manifold gasket. Usually a hose. When I decided to replace all my 35 year old hoses I found 3 cracks/breaks in the large vacuum hose that goes from the idle valve into the plastic boot on the throttle body that I didn’t know/couldn’t see.

I’ll have to triple check them again then, I couldn’t see any cracks anywhere but maybe I missed them.

smoothing out in that range leads me the believe it is a vacuum issue though, maybe the sudden cold weather hardened a hose too much and it cracked

[Dawskip]

Can you provide a video with audio of the engine start up and running/misfiring?

https://youtu.be/_gkz8l_O2tw

[Sunnyledge]

Some thoughts. If this is a vacuum leak it should be a sizable one. If not, assuming you have four properly timed and energized spark plugs firing, this should be an air and/or fuel issue. Is there any chance your fuel is contaminated? It would be nice to know fuel pressure in the fuel rail and if all the injectors are firing. But this takes an appropriate gauge and some work. vacuum line off the fuel pressure regulator and see if any fuel leaks out. Does the flapper move in the AFM. Oddities might include a broken or malpositioned rocker arm causing it to run on 3 cylinders. Since it kinda runs I think rules out a major problem with the DME.

[Dawskip]

Okay reviving this thread.

So I got the car working, it was jacked up, once it got on the ground it ran fine. Ran it better than it ever has for maybe 2 weeks and it died, again. I went to start it one morning, the AFM basically exploded (the bottom that is sealed completely blew off inside my engine bay), I resealed it, and out it back on (also heard a 944 AFM works, tried it and wasn't working for me, maybe I got the wrong one idk).

To recap --

Ive replaced the cap, rotor, plug wires, plugs, fuel pump with a walbro 255 in tank and deleted the inline pump, fresh oil, etc.

The car now wont start up. Fires, but just want start. Definitely smell gas, I pulled the plugs for cylinders 1 and 2 and they look to be completely fouled. What would cause my brand new plugs to foul that fast? They are NGK coppers, am I getting too much fuel from that pump? Would a fuel pressure regulator keep that from happening?

Going to replace the plugs and the fuel filter to see if it does anything, is there anything else I should be trying/investigating?

[packratbimmer]

If it is a 1984, it will not run with a bad coolant temperature sensor. They will warm up and then cut out.