Help me kick my off idle miss/hesitation

[Jordan]

It's an option either way, anyone know what the specs I'd need to watch for are?

[fretburnr]

I'll have to look up for the m42, but for example (iirc) the m20 should see 15-22 in Hg and steady at idle. Those numbers are usually around the same for most every car I've ever looked at.

with the vac pump, apply some similar amount of vacuum directly to the fpr and watch to see if it holds or leaks back to atmospheric. You may not have to remove the fpr to test, but I did for mine.

I also just found this: general chiltons info. Not engine-specific, but should get you headed in the right direction:

2. Chilton general car care manual.

* gauge reading steady 17-22 in Hg indicates normal engine in good condition.
* gauge reading low (15-20 in Hg) but steady indicates late ignition or valve timing, low compression, stuck throttle valve, leaking carburetor or manifold gasket.
* gauge reading steady but dropping regularly indicates burnt valve or improper valve clearance.
* gauge reading dropping gradually at idle indicates choked muffler or obstruction in exhaust.
* gauge reading slowly dropping to zero as engine speeds up indicates choked muffler.
* gauge reading fluctuating between 15 and 20 in Hg at idle indicates stuck valve or ignition miss.
* gauge reading drifting indicates improper carburetor adjustment or minor intake leak at carburetor or manifold.
* gauge reading fluctuating as engine speed increases indicates weak valve springs, worn valve stem guides.
* gauge reading vibrating excessively at idle but steady as engine speeds up indicates worn valve guides.
* gauge reading vibrating excessively at all speeds indicates leaky cylinder head gasket.

[Jordan]

Interesting, thanks. I'm gonna see if any other places in town will rent those out.

[Jordan]

Well I just came back from hopping around all the local auto parts places. They all rent a vacuum pump (the same MightyVac one) and they want $40 deposit. It costs 39.95 to buy it outright. One place didn't have it "in" to rent back out, and the other apparently lost it/it hasn't been returned/come back later maybe we can find it.

No one had just a plain vacuum gauge.

[browntown]

harbor freight sells them cheap. They're pretty reliable for occasional use.

[golde30]

how does the engine sound in the morning? is it loud and kinda sounds like a diesal engine? then after a couple min of driving is all normal? my m42 has started to do this as the weather gets colder.

i spoke to a mechanic, and he swears its just worn hydraulic lifters, and he sees it on every m42 e30+e36.. i dont beleive him, but am going to trouble shoot it for that and see what happens.

[Jordan]

I know the lifters are all fine. Its actually pretty quiet. Even worn so bad it sounds like a tank they won't produce the problems I'm having.

[mattdk318i]

well, Ive owned 4 M42 engines. And i had only one that gave me issues. And it ended up being bad compression on 1 cylinder. And a random ground cable that broke inside the insulation. So when i hit the gas it stretched and died lol.
I would have mentioned the other issues i had. But you already eliminated those.

K.I.S.S

[Jordan]

I created a video for you guys since maybe my description is lacking. Virtual test drive FTW!!

Note that I have purposely driven in a manner that makes it do it as bad as possible so its very clear in the video.

http://oldmary.lqhome.com/~jordansarette/Runsbad.wmv (3.5MB)

[strad]

That doesn't sound like a smooth idle to me. Mine is noticeably smoother and doesn't lope. I'm not saying it to brag, but rather just to alert you that you have problems at idle too. I've driven an M42 that sounded like that (a friend's). He said he hit the rev limiter at 7k though, so maybe it's chipped and that's part of the issue.

[Jordan]

That doesn't sound like a smooth idle to me. Mine is noticeably smoother and doesn't lope. I'm not saying it to brag, but rather just to alert you that you have problems at idle too. I've driven an M42 that sounded like that (a friend's). He said he hit the rev limiter at 7k though, so maybe it's chipped and that's part of the issue.

No I'm not an idiot, but thanks for alerting me that you think I am.

Idle has gotten a lot worse along with the rest of the symptoms since I made the original post. The idle is generally steady in holding around 850rpm or so if you leave it alone. It still misses and varies at idle as well, particularly as of late.

[Jordan]

This morning I popped the plugs out again to check their condition once more. They look pretty much the same as they did last time I checked, which is good.. because to me they look good.

While I was there I did a compression check. Results are as follows:

Cylinder 1: 201psi
Cylinder 2: 195psi
Cylinder 3: 209psi
Cylinder 4: 195psi

All in all pretty good looking numbers, within a reasonable range. I was actually surprised at how well it did.

I also removed the Main and Fuel Pump relays to do the test and while out cleaned the contacts on the relays.

Pulling the vacuum hose off the FPR with the engine at idle doesn't seem to do anything for the FPR. With my thumb over the end of the hose the idle is the same and off idle free revving doesn't seem any different with the FPR seeing atmospheric.

[browntown]

I'm just guessing at this point because it looks like you have a good motor. Have you swapped oxygen sensors with a known good one? I know they're blamed for everything, but just a guess.

[fretburnr]

Those plugs look fine to me.

Pulling the vacuum hose off the FPR with the engine at idle doesn't seem to do anything for the FPR. With my thumb over the end of the hose the idle is the same and off idle free revving doesn't seem any different with the FPR seeing atmospheric.

I think you may have found it. The FPR should open/drop fuel pressure under vacuum (idle, light load) and close/increase pressure under close to atmospheric. ...apparently this one sees atmo all the time or doesn't hold vacuum.

[Jordan]

But if you are right the engine would be running very rich at idle would it not? best I can tell its not as the plugs always come out clean and dry, and the exhaust does not smell like unburned fuel.

Rich running conditions make for wet, sooty plugs.