Sustained low rpm driving causing a bad hesitation...then clears up and is fine?

[nny403]

Update on mine; the pressure regulator greatly helped the issues I was having but it's still going to be narrowed down to the AFM. When it's cold and running a rich mixture it works fine, as the engine warms up the symptoms become apparant again.

The 1800-2200RPM lag seems to indicate the AFM is sending the wrong signal to the ECU. Unless I'm mistaken this is going to have to be the next step.

[dnguyen1963]

^^^Whats the tre?

But the in tank pump is only 4-6psi if thats what your saying.

And dnguyen...where and what brand is the $65 one?

http://www.treperformance.com/FuelPumps/TRE255FuelPumps.html

[strang3majik]

^^^Whats the tre?

But the in tank pump is only 4-6psi if thats what your saying.

And dnguyen...where and what brand is the $65 one?

[Chriskbmx]

you can use the tre as an out of tank pump 2 i have heard. but who knows. i just ordered mine for my 318is.

[dnguyen1963]

Its a Duralast but says BOSCH and Made in Italy right on it. All Duralast ignition stuff is made by Bosch anyway.


Anyone know of any cheaper routes than the stock Bosch unit that are just as good? I just have a hard time spending around $200 for a nothing special inline pump just because it says Bosch on it. All auto parts stores have a similar price.

Tre pump can be had for $65. I have had that unit in my car (single pump '88 325ic) for awhile now...works great so far. You would have to search to see if they offer an in-line pump. I believe that they do. Stay away from AirTex pump...piece of shit.

[ELVA164]

I don't know if this would be what you're talking about, but in the manual for my car it says that if you were driving at low RPM for an extended period or stuck in traffic, it may cause carbon deposits to build up on the plugs. That could cause hesitation and loss of power. It recommends driving at 3000+rpm for x miles to clear them off. Just a thought.

[scott66]

I wouldn't doubt its a fuel delivery problem for the hesitation...being the transfer pump def helped. I'm thinking the inline pump...I kinda want to replace it anyhow, being...I'm making a 1200 mile trip on a 1987 fuel pump on a car with in excess of 200k miles...haha..

I had similar problems with my 85 VW Golf and the culprit was the inline pump...except my issue was that the car just died and would not start again untul it cooled off...

Anyways, I drive my 195,000 mile 1990 325iS all the way from Washinton (the State) to Virginia (thats over 2800 miles) in just about 3 days with no issue, good luck with your drive.

[strang3majik]

are you using a boush cap or a generic one? im just curious

Its a Duralast but says BOSCH and Made in Italy right on it. All Duralast ignition stuff is made by Bosch anyway.


And the hesitation is still there, but much less apparent. It hasn't done the high rpm breakup since the wire and cap/rotor swap though.


I wouldn't doubt its a fuel delivery problem for the hesitation...being the transfer pump def helped. I'm thinking the inline pump...I kinda want to replace it anyhow, being...I'm making a 1200 mile trip on a 1987 fuel pump on a car with in excess of 200k miles...haha.


Anyone know of any cheaper routes than the stock Bosch unit that are just as good? I just have a hard time spending around $200 for a nothing special inline pump just because it says Bosch on it. All auto parts stores have a similar price.

[Chriskbmx]

Welp...replaced the cap and rotor again for the hell of it since they were under warranty and checked the wires while I was at it an they were arcing like mofos.

Replaced them as well with another used set I had...no more high rpm breakup.

Like I said this was only after a few mile drive. Ill be driving it all around tomorrow so ill keep everyone posted.

are you using a boush cap or a generic one? im just curious

[nny403]

Welp...replaced the cap and rotor again for the hell of it since they were under warranty and checked the wires while I was at it an they were arcing like mofos.

Replaced them as well with another used set I had...no more high rpm breakup.

Like I said this was only after a few mile drive. Ill be driving it all around tomorrow so ill keep everyone posted.

Please do, I'll report in on the pressure regulator if I can get the symptoms to duplicate and see if we can't tidy up the fixes in a single thread. Searching on this forum is a bit limited.

[strang3majik]

Welp...replaced the cap and rotor again for the hell of it since they were under warranty and checked the wires while I was at it an they were arcing like mofos.

Replaced them as well with another used set I had...no more high rpm breakup.

Like I said this was only after a few mile drive. Ill be driving it all around tomorrow so ill keep everyone posted.

[85e325]

Im having a similar problem with my 85 M20b27. When Im cruising around between 1500 and 2000 rpm then accelerate it will drop about 400 rpm and hesitate for about 5 sec and then smooth out. Here's what Ive done to it so far...

cap, rotor, plugs and wires
timing belt
air and fuel filters
cleaned MAF and injectors

I do have a moderate exhaust leak right behind the muffler, would something like that cause it? Its not effecting my gas milage or the driveability of the car, its just REALLY annoying.

[nny403]

NNY403...its more or less random. The hesitation is only after driving at low rpms though.

And I'll be honest, after the new transfer pump, it hasn't done it yet, but I've only probably put 20 miles on it so far, so I'll keep ya'll posted on that.


But the brick wall/breaking up at 4k is still there, and is also random. It does seem like fuel starvation, but fuel pressures were in check when I checked them a month ago. But maybe the old dying transfer pump overstressed the main pump and now its dying.


I'm going to check the distributor cap again...make sure it didn't crack again....just looked at it today and it isn't sitting entirely flush :/

The same symptoms are happens with mine as well, but prior experience points to pressure regulator issues. Happened a lot with Datsuns. BMWs seem to be less clear in their diagnostic procedures. Replace this part, cry, and then replace another part. Not the most viable method.

[strang3majik]

NNY403...its more or less random. The hesitation is only after driving at low rpms though.

And I'll be honest, after the new transfer pump, it hasn't done it yet, but I've only probably put 20 miles on it so far, so I'll keep ya'll posted on that.


But the brick wall/breaking up at 4k is still there, and is also random. It does seem like fuel starvation, but fuel pressures were in check when I checked them a month ago. But maybe the old dying transfer pump overstressed the main pump and now its dying.


I'm going to check the distributor cap again...make sure it didn't crack again....just looked at it today and it isn't sitting entirely flush :/

[nny403]

A brief fuel starvation can cause your problem. Was your gas tank near empty when you experienced the symptoms? I would tee in a pressure gauge and monitor the pressure while driving.

Jumping in on this thread, I have the exact same symptoms. Is on your 325 the issue coming up more or less randomly? Or after the car has been driven to full operating temperature then shut off then started back up?