1992 525i project runs rough

[wiebuschk]

1st let me say this is a Great forum. The wealth of knowledge here is incredible. I have learned a ton about my car just from searching. I was previously signed up as Buschman but could never post for some reason.

Here's what we have. 1992 e34 with the m50 engine & a 5 speed. This is a project that was for my 15 year old son & I which we bought for $350. It's not real pretty but the leather was good & it ran & the AC worked.

We have put in a clutch, A rear bearing, A general module for a door lock & window problem, & a center tie rod. We are still OK money wise but we probably won't have any body work done. It is now inspected & street legal.

It doesn't run as smooth as it should. It bogs down & almost shudders in low rpm. If I am in 5th gear going 65mph & floor it it just shakes & slowly speeds up. It idles fair but not like it should. 5000 to 7000 rpms feel pretty good. It seems to run a little better when it's cold. I can feel it miss sometimes & then smooth out. I get an occasional intake backfire.

Car has over 180# compression in each cylinder. It has new plugs. It has 17 inches of vacume at idle.The old plugs looked great. A BMW mechanic told me if it was a vacume leak that was bad enough cause this much problem it would throw a check engine light & a code. The only code is a 1444 which means there are no codes. I have run one can of Techron through it but plan to run more. I do think the car sat up for a while. The TPS checked ok with a meter.

I have previous experience rebuilding a 1985 K100 rs bike which ran like ass until I cleaned the injectors so I am leaning this direction.

Any good ideas? Thanks in advance!!

[Jon K]

You failed to mention the mileage but some things I would check:

I would suspect perhaps a leaking injector. If you're getting back fires in the intake that is most likely the culprit I would think - the car is sequential injection but the OBDI aspect makes it impossible for it to detect misfires. 17" is decently good for a '92 525 mine holds about 17 - 18". The only thing is, for a backfire to happen in the intake the timing could be off but I am not entirely sure - it could be running lean on one cylinder and heating the valve and the fuel igniting that way - not entirely sure.

I'd like to know how many miles are on it though. The fuel reail is S I M P LE to pull so it'd be a good idea to pull it and have a look see.

[632 Regal]

you covered most of the bases, thanks for the searches. I would recommend a computer reboot which will set all codes gone and you will have fresh to start with. If the codes are never reset the same issue will traspire even tho you replaced the failing items indicated. Wait after you reboot the computers and post again, hopefully your troubles will go away.

good luck and the best.

[wiebuschk]

If rebooting is unhooking the battery for 10 minutes & hooking it back up, I've done that. The car has 180k. I have sprayed wd40 around the injectors when running & it does not speed up. My thinking is that when it runs bad it is under a load so vacume would do higher. Maybe that is when the vacume leak occurs.
By leaking injector you mean an air leak around the O-ring seal?

[jjdickm]

a leaky injector usually means it is not closing the valve completly and you have un measured fuel going into you engine. causing one of you cylinders to run extemley rich. If thats the case replace the injectors and your car will run fine. The thing that bothers me is you said the plugs looked good. I would probably try to find the manifold leak. check all the intake boots for any cracks or gaps. Good luck!

[scott 4991]

Some thoughts - plug wires? Dist cap? O2 sensor? I recently ran a vacuum guage out the back part of the hood and taped it to my windshield, just to see what the vacuum was doing. MAS - checked? There is a procedure in the Bentley book, looking for a glowing wire - I have not done, but read about. What about the center bearing (in the driveshaft) and the engine and transmission mounts - easy to replace, just did mine.

Keep us posted.

sc

[kesslerbmw]

I am having a similar problem, my car will start missing bad on one or even two cylinders (4&5) and I thought it was coils. I swapped the coils, ran ok for a day or two, problem came back, swapped the plugs. Ran ok for a day or two and the problem came back. I havent jacked with the injectors yet, but Im going to try when it warms up around here.

Have you cheked the coils? Doesn't seem likely, but it may be worth a check.

Also you can use an ice cube on the exhaust manifold to pinpoint which cylinder that is giving you trouble. Obviously the cylinder that is missing will not melt the cube nearly as fast.

[tree18is]

i wish i could help you out... always good to add a fan to the bimmers.

[Jon K]

Some thoughts - plug wires? Dist cap? O2 sensor? I recently ran a vacuum guage out the back part of the hood and taped it to my windshield, just to see what the vacuum was doing. MAS - checked? There is a procedure in the Bentley book, looking for a glowing wire - I have not done, but read about. What about the center bearing (in the driveshaft) and the engine and transmission mounts - easy to replace, just did mine.

Keep us posted.

sc

No plug wires, no dist cap. These are coil on plug cars. If his coils were misfiring frequent enough his plugs would be carboned up.

It's either a leaking injector (Leaking fuel, not air) that puddles on the valve more than it's intended and igniting, causing the backfire out of the intake, or its a vacuum leak doing the same.

Nothing about the driveshaft or engine mounts would cause this.

I know it sounds like a big job, but remove the intake manifold and buy new O-ring gaskets for the intake manifold (they're relatively cheap). They tend to get weird at around 150k. I replaced mine. I used to have a backfire in the manifold as well. No more.

If that doesn't do it, look for cracked or damaged throttle boot and ICV lines etc - if you backfired enough you could have cracked anythign plastic or rubber.

[wiebuschk]

Thanks again for the replies gentlemen. I have been tempted to pull the intake just to check the vacume lines & clean up the ICV beneath it anyway.I didn't know what kind of gasket I would run into. Is RTV against the law for this application? It works on GM's & Fords>

When an injector leaks is it because it's gooped up or is it faulty?

BTW I just love the way this car drives. I would like to get a touring version someday!

[Jon K]

When we talk about intake gaskets, we are talking about injection molded rubber/plastic ones. You will NEVER seal an M50 intake manifold correctly trying to use silicone.

http://autohausaz.com/secure/PartImages/11611717259.jpg


six of those

[kesslerbmw]

Jon is right, save yourself a lot of work and heart ache by just picking up some new gaskets. They are pretty cheap too.

[wiebuschk]

Thanks ya'll.
I couldn't stand it so I tore it down. The seals were pretty flat. I didn't have new ones yet so I turned them over. The inside edge still had a nice ridge on it which stuck out from the manifold. No difference in performance. I have new seals ordered but I think these are probably sealed for a while.
I put 40# of air pressure on the fuel rail & energized the injectors. All had a great spray & did not leak. I know ,I could have blown myself up but I was careful & only blipped the injectors.
Again it runs worse when warm if that's any clue. A friend has an ultraviolet thermometer. I am going to check for a cold cylinder. It is not backfiring like it was. I wasn't bad before. I guess it feel like more of a missfire.
Should I have it diagnosed by a machine?

[wiebuschk]

Could an O2 sensor be causing my grief. Temp sensor? TPS? I checked it with a meter but I guess it could still be a wrong readind for the car.

[wiebuschk]

Could an O2 sensor be causing my grief. Temp sensor? TPS? I checked it with a meter but I guess it could still be a wrong reading for the car.

[Ross]

Sounds lean to me. Look for vacuum leaks.
Any pinging or noises on throttle opening?

[scott 4991]

Is piniging a sign of leaning out? I don't often 'step on it' on my car, but did the other day, sort of testing things - and noticed when the RPM was around 5K there was lots of pinging, so I let up and it stopped. Could this be a sign of leaning / the O2 sensor being bad?

sc

[wiebuschk]

There has been no pinging. I guess I need someone to put an exhaust gas analizer on it.

[wiebuschk]

I finally put the new intake gaskets in as well as injector seals & valve cover gaskets. The car seems to run better but still not 100%. I've unhooked the battery until tomorrow. I'll drive it tomorrow & let it remap. It still seems like a closed loop issue. It runs pretty good when it's cold. I'll update.

[acidfire52]

You car sounds very similar to mine. But, mine does it worse when it is cold.

I replaced my intake gaskets, intake boot, and a number of hoses under the intake, cleaned the ICV, and it does seem to run better. Read a posting by another user here that was having similar issues and his problems were solved by replacing the DME, ie engine computer.

These early M50s seem to be very picky about running smoothly...

Just my $.02

[Guapo]

Check your coil boots for arcing inside the spark plug tunnel inside the head. I had similar symptoms when I had a bad boot.

[wiebuschk]

What would an arcing boot look like?

Drove it today. Runs better but not right. I still think its lean but there is no vacume leak that I can find. ??

What could cause this that would not throw a code?

[wiebuschk]

The problem ended up being a bad #2 coil. Found it by pulling coils one at a time. When I pulled the #2 the way the engine was running did not change. I still have a slight stumble off idle if I nail it but it is much better than it was.
Thanks for all the advice!

[Dave M]

Thanks for following up. I've been following the post and appreciate it when the culprit is reported.

[foemill]

I've been following this thread and my '95 525iT has been having identical problems. I checked the coils and they all read 7.9 - 8.0 ohms though. did you check your coils as well? The rough low-end performance has been driving me crazy! And like yours, it runs great before the car warms up. I'll try pulling the coils one at a time for a sanity check. Were any of your plugs wet at all?


The problem ended up being a bad #2 coil. Found it by pulling coils one at a time. When I pulled the #2 the way the engine was running did not change. I still have a slight stumble off idle if I nail it but it is much better than it was.
Thanks for all the advice!

[genphreak]

Thanks for following up. I've been following the post and appreciate it when the culprit is reported.Did anyone resolve the great M50 mystery? I've found similar threads around- at least 10 other occurences of intermittent stumbling as if 2 cylinders died whilst running- but then they cut back for apparently no reason. I also get the occasional intake backfire on cranking.

No solutions have been found, excepting the intake gaskets Jon was suggesting.

Is this a vacuum leak after all? I'm almost sure it can't be on mine- I've done everything. Next step for me is the O2 and temp sensors... then it gaskets :(.

Any suggestions would be greatly appreciated of course.

[genphreak]

I generally fixed the engine backfire, dodgey running and slow (500rpm) idle by replacing vacuum pipes... what so clearly seemed to be a coil or a plug or a cylinder was actually the vacuum pipe between the cam cover and the intake junction (plastic pipe leading into the intake manifiold behind the throttle body). I've checked the Idle Control Valve, the throttle body, all the other connections (ie 'PCV' and throttle hoses off), I don't know why I didn't check the front one... it also has a white o-ring, so no doubt that has to come out.

So don't go off symptoms with your troubleshooting, what the computer thinks when you have a vacuum leak will make it do unexpected and weird things indeed.... :) Nick