'87 ETA Hesitation on Acceleration

[thedivision]

Hi all,

I'm having a hesitation issue with my 2.7 m20, auto. When driving, sometimes it just doesn't want to move. It feels like you're in a high gear at very low rpm. I'll floor it and it will just play dead and slowly accelerate. You can hear the engine struggling. At some point around 3k, it kicks in and shoots off like normal.

Some more information:
- at cold startup, the idle bounces around for about 15-20 seconds (800-1400rpm) and then settles normally
- this issue has really pronounced itself after seafoaming the engine through the fuel pressure regulator vacuum line - not sure if the two are connected
- the car get's TERRIBLE gas mileage (it did before this issue too) - around 210 miles to a 55L tank, mostly highway
- happens when the car is full (2 or more people) more often than when I'm by myself
- the external fuel pump hums, but did so before - I will check to make sure the in-tank pump is still working by unplugging it and seeing if the external reacts
- I changed the plugs to newly gapped NGKs, no difference
- this is a Motronic 1.0 car, so there are no CEL codes to check

As always, your help is appreciated.

Thanks

[paperplane94]

check to see if the fuel pressure regulator is leaking out of its vacuum hose, torn diaphragm.

[BoxDriver86]

Torn elbow boot to the throttle body or other random vacuum leak is likely the culprit. If you have removed your injectors lately, make sure they are sealed. As far as MPG goes, this in conjunction with an O2 sensor is what made mine shoot up.

[nebulous123]

AFM is my guess. I still need to rip mine apart and reset the dial and clean the contacts. Also someone mentioned that the TPS might be bad and not reading that its WOT so it doesn't react till after 3k. Just a thought

Maybe a smoke test for vacuum leak?

[thedivision]

Thanks for the replies. The problem doesn't occur all the time, but it is definitely getting worse, and does occur more often when there are others in the car. Uphill is worse than downhill. I paid closer attention today, that 'kick' I mentioned earlier occurs just before 2500rpm. The fuel economy gauge is steady throughout the hesitation.

I seafoamed it through the FPR hose, no fuel came out. Assuming it's good?

I will inspect the elbow boot. I haven't removed the injectors.

Is the AFM rebuildable (DIY)? I have an '89 325i parts car with a 2.5L - can I swap the AFM or oxygen sensor from there?

[paperplane94]

If fuel doesn't squirt its probably fine.
i think the AFM's have two different resistance tracks so it might not work.

You can certainly test the old AFM with a DMM though:
http://www.iprimus.ca/~trauttf/temp/AFM/

[AT-JeffT]

My Eta was dieing when it would go uphill, and very sluggish. Turned out to be a cracked Distributor Cap.

http://www.e30tech.com/forum/showthr...hlight=bucking

[thedivision]

Hi all,

I lifted out my rear seat to test the in-tank fuel pump. I disconnected the wires and there was no change is sound or feel in the in-tank or inline pump. This leads me to believe the external/inline pump is doing all the work. I'm hoping this is the cause of the hesitation.

I'll replace the pump and update.

Thanks

[thedivision]

Update:

I fixed the transfer pump. The car drives a lot better now, but still hesitates sometimes.

[rodpaine]

Update:

I fixed the transfer pump. The car drives a lot better now, but still hesitates sometimes.

Check the output pressure of the Fuel Pressure Regulator. I had one that was allowing gas to pass back to the tank on an intermittent basis, dropping the pressure and causing much the same kind of issue you're having. I talk about it here.
-Rod