1995 525i miss on acceleration

Looking for some ideas on stumbling/miss that shakes the car under load. In the morning on startup she idles rough but once you accelerate lightly she smooths out. (iff you accelerate too hard it will start missing violently) As she warms up it might miss occasionally at idle and seems to run smoothly on light acceleration (again press the gas too hard and the car will miss and shake violently) However, once the car passes 3000rpm she seems to clear and run great. No CEL or codes present. Just replaced fuel filter. 3 coils were replaced a year ago with Bosch coils. Car has 160,000 miles. Any input is appreciated. Thanks!

When was the last time spark plugs were done? Usually if a motor misfires, it's throw a CEL...so it's weird that it stumbles hard enough to make the car shake but will not throw a code.

Not sure when the plugs were done, but I just pulled one and it looks good. They are Bosch 2+ Platinums (with the two prongs on either side of the ignitor)

Have seen a fault where the ceramic nose is broken and slides down and masks the spark. Gives a fault as you describe. Next is leak out from a coil-pack. Injector clean (remove and clean/check on rig type) wouild be last.

Just replaced all vacuum lines intake gaskets and throttle body gaskets as well as intake boots and hoses and injector o rings. Basically anything that could cause a vacuum leak. The car has a bit more power and increased fuel efficiency but still has the stuttering miss on acceleration. On an interesting note, I accidentally left the vacuum line to the fuel pressure regulator off on my test drive. Upon discovering this I hooked it back up and the car started missing worse! Could the FPR be the problem? Even though it was not hooked up to vacuum the car stool ran good(even with the miss). Or do you think the fuel pump might not be putting out enough pressure?

Originally Posted by Bimmerfan84

Just replaced all vacuum lines intake gaskets and throttle body gaskets as well as intake boots and hoses and injector o rings. Basically anything that could cause a vacuum leak. The car has a bit more power and increased fuel efficiency but still has the stuttering miss on acceleration. On an interesting note, I accidentally left the vacuum line to the fuel pressure regulator off on my test drive. Upon discovering this I hooked it back up and the car started missing worse! Could the FPR be the problem? Even though it was not hooked up to vacuum the car stool ran good(even with the miss). Or do you think the fuel pump might not be putting out enough pressure?

If your FPR is bad it will squirt fuel into the intake and cause a hesitation/rich running condition like no other.
If you remove the FPR vacuum line and it smells like fuel then you need to replace the FPR as it is causing a rich condition.

Check your throttle position sensor. Its a little switch next to your throttle body. Unplug it, clean both the switch and the plug with contact cleaner, apply dielectric grease to both and fix it back. Then restart the car and see.

Check your error codes, there could be important clues there.

Ran fuel pressure test rail reads 41-43 psi at idle and jumps up to 50 when you rev it. If I disconnect the vacuum from the fpr it reads 54psi. Smoke test done, no leaks.

Originally Posted by Bimmerfan84

Just replaced all vacuum lines intake gaskets and throttle body gaskets as well as intake boots and hoses and injector o rings. Basically anything that could cause a vacuum leak. The car has a bit more power and increased fuel efficiency but still has the stuttering miss on acceleration. On an interesting note, I accidentally left the vacuum line to the fuel pressure regulator off on my test drive. Upon discovering this I hooked it back up and the car started missing worse! Could the FPR be the problem? Even though it was not hooked up to vacuum the car stool ran good(even with the miss). Or do you think the fuel pump might not be putting out enough pressure?

Have you taken a look at your fuel injectors? Are you getting any injector codes ? It is possible to hold your fuel rail up and out of the intake manifold's insertion points without dismantling anything else, and, while cranking your engine, visually observe the fuel spurting out from each injector. If you do this, be sure to unplug each ignition coil first, you don't want first. Check youtube for videos on how good injectors should spurt their fuel.

When I did the o rings I checked all injectors. They are extremely clean but I let them sit in cleaner before I reinstalled them

If you read the maintenance threads at the top of the forums, then you know that you should change out your fuel pump, fuel pump/abs/dme/o2 sensor relays, and the crankshaft position sensor, to eliminate common e34 no-start situations, unless they were done within the past 2-4 years. Use only oem stuff, and since you seem to know your way around the car, you'll save on labour.

These might end up fixing the issues that you're having, and you need to do them anyway imo.

Yes, it could be the fuel pressure regulator as well from the sound of it, but then if your fuel injectors were functioning normally upon inspection...it does not seem likely.

Did you check and clean out your throttle position sensor like I suggested earlier ? Did that help ?

Originally Posted by Bimmerfan84

Not sure when the plugs were done, but I just pulled one and it looks good. They are Bosch 2+ Platinums (with the two prongs on either side of the ignitor)

Unless you know which cylinder was missing, please check all of the plugs.

And are you getting any useful error codes ??

Originally Posted by robertobaggio20

If you read the maintenance threads at the top of the forums, then you know that you should change out your fuel pump, fuel pump/abs/dme/o2 sensor relays, and the crankshaft position sensor, to eliminate common e34 no-start situations, unless they were done within the past 2-4 years. Use only oem stuff, and since you seem to know your way around the car, you'll save on labour.

These might end up fixing the issues that you're having, and you need to do them anyway imo.

Yes, it could be the fuel pressure regulator as well from the sound of it, but then if your fuel injectors were functioning normally upon inspection...it does not seem likely.

Did you check and clean out your throttle position sensor like I suggested earlier ? Did that help ?

The functioning of the fuel injectors had nothing to do with the fuel pressure regulator. You can't assume that the FPR is fine if the injectors are working.

In general i would agree with you but in a case of a misfire, which I assume is only happening on one cylinder, then if the injectors are fine then the regulator should be ok. If the regulator is screwed, all the injectors will be performing poorly and not just one of them. The car would be either running super rich or would feel uniformly underpowered and strained, instead of a misfire in one cylinder. If a bad fpr leads to misfires, then all the cylinders should be misfiring.

Please advise if my hypothesis is correct. Thank you.

Okay so it was a failing coil. I bought one and swapped it around until I got to cylinder 3 and the car ran great! Plan on replacing the other three coils that have not been upgraded to bosch yet shortly. (I already had replaced two before) This is the first time a coil has done this to me before, usually they either throw a code or die completely.

Originally Posted by Bimmerfan84

Okay so it was a failing coil. I bought one and swapped it around until I got to cylinder 3 and the car ran great! Plan on replacing the other three coils that have not been upgraded to bosch yet shortly. (I already had replaced two before) This is the first time a coil has done this to me before, usually they either throw a code or die completely.

Very peculiar that a lousy coil did not throw a code. Is this normal (for components to get busted yet not throw a code) ?

From what I understand. The coil can be going bad (only missing under load, randomly missing, arcing out)but the DME can still read it so it doesn't throw a code until the entire coil has stopped working.

Here are some tell tale signs on coils that could be having issues. Do you see the hairline cracks? Even if the coil is still working it can arc and get moisture inside that will damage the coils ability to fire properly. I stupidly did not notice because I never closely inspected them.

Nice Catch there with the coil!

And I see your point now Roberto, I was thinking very generally not specifically to this problem.