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940 Let's fix McLovin's car!

Tamnakz

Tamnakz

Active member
Joined
May 28, 2006
Location
Lansing, Michigan
So. . . We did alot of looking around on McLovin's 940 turbo today.

Basic history:
Bought non-running.
Got it running.
Broke exhaust studs.
Got rebuilt Fleabay head.
Installed head along with conical 15g.

The car has two problems that appear to be seperate.

Problem 1:
The car has a 'stumble' at 1500rpm. ALWAYS 1500. If it were an LH2.2 car I'd say hall sensor, because the tach drops, but the engine RPM's dont . . . Sometimes it'll hold at 1500 regardless of throttle, and the tach will keep dropping off to 1k or lower, but right back up. Other times, it'll just caugh and stutter a second and then keep going.

Problem 2:
Cyllinder 1 is intermittently dead. It'll cough and jump when it no-fires, and the normal signs of fuel going through the exhaust are apparent.

Now. . .first I'll go through what we tried for Problem 2.
We checked fuel pressure. . . My gauge won't fit with the rail installed, but with it pulled out and just turning the key to run to turn on the pump, it put out 45psi no problem.
The injector sprays a good mist, no dripping or bad seals there.
Compression is 150 130 145 145. . . not great, but we knew that was coming.
The AMM has been verified good.
The mani gasket has been verified good as best as possible. Carb cleaner makes no difference
We used an accurate vacuum gauge to see if maybe a valve wasn't sealing. Figured we'd see a drop in vacuum when the cyllinder was supposed to fire if there was a bad valve, nothing irregular.
Timing is right around 11 BTDC.
Mechanical timing is good.
We spent an hour or two checking/verifying wiring.

We DID find a bad ground on the firewall (for headlights) after some backfeed issues. When he'd turn on his brights and his fogs were already on, the car would die. Played around and found a corroded ground block.

He'll be cleaning the grounds there further, as well as the grounds on the inside kick areas by the ICU/ECU.

For problem one, we didn't do alot of looking/diagnosis. In fact, almost none. . . It acts like the computer is shutting off for an instant, over and over. . . Like I said before, if it were LH2.2 I'd be looking at the hall sensor.

Any suggestions? I'm sure I missed telling ya'll about a few things we checked. . .
 
Since this car is LH2.4 I'd look at the engine speed sensor on the bell housing behind the engine. If it's still an original sensor it needs to be replaced. I'd also check the grounds on the intake manifold and clean them. Also make sure the power stage is mounted tight on the inner left fender. I'd also suggest cleaning the coil terminals and make sure they are tight. Be sure there isn't any dirt built up on the coil.
 
The engine speed/cp sensor is brand spankin' new with a good signal.

Grounds on the manifold were pulled/filed/re-installed when we checked the fuel rail.

Coil connections were filed as well when we were checking compression and hooking/unhooking it.

I didn't do anything with the powerstage, but McLovin told me he'd had it off and cleaned a few days earlier working with the car.
 
I do not have the answer, however, due to the tach dipping at 1500 rpm, it has something to do with primary ignition. HS, coil, wiring, ign amp,fuse, ignition switch. vacuum leaks due to staying at 1500 by itself. Start over and verify. Just thoughts, good luck.
 
First read fault codes.
Note them down, if any.. Clear ECU and EZK fault codes.

My guess is:
Ignition components..

Do a proper stage 0, which should always be done, even if you buy a car with no problems :-) It sucks when your car breaks down due to the prev owner not maintaining it properly :-) (exception beeing if the prev owner just did a stage 0, then you can drive a year before swapping oil and a couple of years before swapping plugs and such things).
 
UPDATE:
I drove the car back home last night with no issues and then I started it up this morning and it didn't misfire at all! This could be a fluke, but I'll be driving it around some more to see if it's going to stay like this.


Need For Swede said:
I don't suppose you have an extra ECU laying around you could swap in for a test?
Click to expand...

I bought a 937 ECU with a Viking EcoMax chip in it from Ruben and have already swapped that in. So the ECU should be good.

DaButcher said:
First read fault codes.
Note them down, if any.. Clear ECU and EZK fault codes.

My guess is:
Ignition components..

Do a proper stage 0, which should always be done, even if you buy a car with no problems :-) It sucks when your car breaks down due to the prev owner not maintaining it properly :-) (exception beeing if the prev owner just did a stage 0, then you can drive a year before swapping oil and a couple of years before swapping plugs and such things).
Click to expand...

No fault codes are being thrown. Like at all. Anybody know what controls the check engine light?
Pretty much all of the ignition components are in good shape or new so I don't think the issue lies there. I think I'm going to pull the EZK computer and see what that looks like. Anybody know where that is?

Chris_R said:
'Cleaned' as in removed all the dielectric and/or heatsink grease?
Click to expand...

Yeah, I wire brushed all the contact surfaces and sprayed WD40 on it. Does it need dielectric grease?
 
It's LH 2.4 and you've changed some stuff on it. It will probably settle down all by itself. if not, reset the ECU.

Regards, Andrew.
 
Typhoon said:
It's LH 2.4 and you've changed some stuff on it. It will probably settle down all by itself. if not, reset the ECU.

Regards, Andrew.
Click to expand...

I've driven it about 7 to 800 miles since the new stuff has been on it and it's still ****ed.

The misfire came back when I drove it later today. It just ran on 3 cylinders for the entire time pretty much. Only time it's alright is if I'm giving it light throttle to coast when I'm up above 2k rpm.
 
So I drove it again this morning and it did the same routine where I drove it home from my friend's about 4 miles and it ran fine. No misfire. Then I drive it later and it's running on 3 cylinders everywhere, except when I lightly press my foot on the gas to keep it coasting. This continued until I had kept it running that way for a while. I usually have to keep it downshifted in 2nd when I'm driving through town around 35 mph.

This makes me think it could possibly be a failed intake manifold gasket. It would explain my being able to boost only a 1/4 inch into the white.
 
We checked the intake pretty well with that carb cleaner. We would've seen at least something if it was bad.

Did you do those grounds?
 
are you fouling the plug on that cylinder? is it fuel that is causing the misfire, or is it spark that is causing it? if its spark you should foul the plug....just some thoughts.
 
mike240dl said:
are you fouling the plug on that cylinder? is it fuel that is causing the misfire, or is it spark that is causing it? if its spark you should foul the plug....just some thoughts.
Click to expand...

It's neither. It's got good spark and we pulled the injector and test fired it.

I haven't done the grounds yet. I haven't had time, but my plans of heading to Seattle may not be happening so who knows.

I'm gonna replace the intake manifold gasket probably today or tomorrow.
 
yeh that gasket on my 87 740 caused a huge power loss until i popped the hood and noticed the problem. Intake manifold gasket is easy to change.. u might look at putting in another crank sensor or engine temp sensor if u havent already. may as well if u havent since you will have the intake off.
 
doeboy said:
yeh that gasket on my 87 740 caused a huge power loss until i popped the hood and noticed the problem. Intake manifold gasket is easy to change.. u might look at putting in another crank sensor or engine temp sensor if u havent already. may as well if u havent since you will have the intake off.
Click to expand...

I'll probably pop in another ECT while I'm at it.
 
Woooooooo!

Well, turns out the old check once and check again 9 times is a good idea. It was a fouled spark plug that I somehow managed to keep in the head for 4 weeks.:oops:

Anyway, now it just stutters around 1900 RPM. I'm assuming it's some messed up spark signal. The tach bobbles and drops, it will stay and get stuck just above 1k if I press the gas just right. It is definitely a cylinder not firing because of the sound.
 
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