Starts/Idles/cuts out try to rev the engine

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6carlovernc

Starts/Idles/cuts out try to rev the engine

Post by 6carlovernc »

My car will start and idle fine. I can raise the RPMs gradually and all is find. If I try to rev the engine it will bog down, hesitate, sputter and eventually cut out. I can restart and it idles fine but can't raise RPM's fast. Did it the other day and could rev easily after replacing fuel pressure regulator. Cut car off and came back about 5 min later and tried to rev and car sputtered, tried to regain idle but eventually cut off. Have replaced fuel filter, pressure regulator, will try different AFM soon. Any ideas or suggestions?
bpoliakoff
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Post by bpoliakoff »

Sounds like a fuel issue. Did you use a new FPR or just throw a different one on. Check both the in tank and external fuel pumps and test with an in line pressure gauge.
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mitchcornacchia

Bump on the fuel pumps

Post by mitchcornacchia »

Check fuel relay also could be in its death throws! Fuel filter ?????
Pod
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Post by Pod »

Definitely sounds like fuel problem. Check the pipes between the tank and the filter. They can get blocked with rust, but still let a little fuel through!
6carlovernc

Post by 6carlovernc »

Thanks everyone for your suggestions. I will check those items. FYI...I replaced the in-tank pump and the fuel filter. I replaced the fuel pressure regulator with a new one.
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Brucey
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Post by Brucey »

I'd suggest the following tests (after checking everything for air leaks of course...)

1) fuel delivery check should be ~1 litre/min through the FPR

2) fuel pressure check; should be 3 bar or 2.5 bar on early models), varying with inlet vacuum.

3) ignition check; test for ability to fire sparks ~1/4" to ground on each plug lead.

4) check dizzy cap and rotor arm

5) check AFM voltage output

hth

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
6carlovernc

Post by 6carlovernc »

Thanks guys for the information. Just want to give update. Had opportunity to change AFM and eliminated it as an issue as it improved idle but only momentarily. Seems like issue is associated with engine temp as I unplugged the O2 sensor and notice decline in idle. Re-plugged and car improved noticebly. Improved to point where idle response was about normal and drove up and down driveway without a hint of any hesitation. When engine temp reach midpoint on gauge problems of hesitation and loss of power returned. Was barely able to get it back into garage. Definately going to focus on fuel issue but do you think the O2 sensor may be the issue? Thanks.
Pod
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Post by Pod »

Have you checked the cold start components and also the sensors on the thermostat housing? Since unplugging the 02 sensor caused a difference in running, I would guess that this is probably working OK?
6carlovernc

Post by 6carlovernc »

Took car to mechanic. He took cat off and car was able to reach 55 to 60 mph when normally car would cut off or out once reached normal operating temp. Car ran up to 55 - 60 and then cut out/off lost power. Any ideas? Focusing on fuel quality. May be some trash in there getting to injectors. New in-tank pump, new in-line pump, new fuel filter, new dizzy cap and rotor. Don't understand. Could ECU be part or problem, or throttle position switch. Any suggestions appreciated.
Chris Wright

Post by Chris Wright »

What year and model car?

Check the Throttle Position Switch, it may not be giving the off throttle signal and check the WOT (Wide Open Throttle) position also.

Check the vacuum line from the top of the Fuel Pressure Regulator for leaks and that it is hooked up to the bottom of the intake manifold with no plastic check valve in the line.
6carlovernc

Post by 6carlovernc »

Thanks alot. The mechanic says that he has checked all of those items and they did not have an effect.
Area 52

Post by Area 52 »

A friend of mine had a cracked fuel hose between the intank pump and the external pump on his E23. Under load, it sucked air. If it hasn't been replaced, use the old hose to pull in the new hose to eliminate the need to drop the tank.
Budget M3
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Post by Budget M3 »

Was this ever resolved? I have a very similar issue with my 1985 M635.

In my case it is intermiittent, but definitely appears to be heat related as cold start is fairly normal. Idle is smooth (once I replaced the plugs, dist cap, and rotor--all of which were very crusty). The fuel can seemingly cut out at any time once warm and especially when it is very hot. I can be travelling at low speed/rpm or sitting at a stop light and the car can cut out. Giving it some gas or feathering the throttle can usually keep the car running.

One additional odd symptom is that after cold start, the ABS and oil pressure lights stay lit and the engine cuts out unless I tap the gas. Tapping the gas encounters a short hesitation, but the warning lights go out and it idles normally after that.

I really hope it's the FPR (cheap and easy to replace) and not the cold start valve or fuel pump(s) whiich are more involved and expensive.
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'90 Z1 Top Red
'91 850i Mauritius Blue
'85 M635CSi Alpine White
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'16 340i Med Blue
grandson
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Post by grandson »

Hi,
I had a similar problem and was certain it was fuel until i had checked everything and nothing else to check on the fuel side.
When I started checking the ignition I found that the rotor button arm had 'corroded' yes corroded or chemically broken down. Once i replaced that everything was fine.
02'sandsix
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Post by Budget M3 »

grandson wrote:Hi,
I had a similar problem and was certain it was fuel until i had checked everything and nothing else to check on the fuel side.
When I started checking the ignition I found that the rotor button arm had 'corroded' yes corroded or chemically broken down. Once i replaced that everything was fine.
Well, I already have a new rotor, so that's not it in my case. I did find the vacuum line from the FPR to the mainfold was secure but not "completely" tight. Let's hope that fixes it.
Image
'89 Z1 Dream Black
'90 Z1 Top Red
'91 850i Mauritius Blue
'85 M635CSi Alpine White
'03 M3 Conv, Imola Red
'16 340i Med Blue
6carlovernc

Post by 6carlovernc »

Update:
Problem still not resolved. However, a second, more experienced technician is looking at it and beleives the problem is in the electrical harness. Had a similar problem with a car that had just had an engine replaced and found it was the brown wire in the engine harness. Waiting to hear back and will update when word is recieved. Thanks for continuing to look and post.
nc6carlover
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Re: Starts/Idles/cuts out try to rev the engine

Post by nc6carlover »

Its been a while since I posted. Had to re-register and change username. Life has a way of getting in the way! Anyway the problem I had with the car cutting off when it got warm took alot of patience and persistence but so that other know the problem I had was in the exhaust system. The top side of the muffler had a hole in it that was not distinguishable in terms on sound so it was not until I removed the exhaust that I discovered the issue. A neighbor had told me he had a similar problem and he found that inside his muffler the material, whatever had come loose and would prevent air passage thus causing the problem. Once I replaced the system, no more problem. Just wanted to finally give an update. Still working on it, not registered yet but I can drive it and it drives good. I hope to go to the vintage this year in Asheville, NC. We will see. Thanks for your input.
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