UPDATE: Stuttering at 3k RPM.. has anyone figured this out? --- VIDEO INSIDE

[Brian318is]

Ok, I've searched all three great e30 forums (r3v, e30tech, m42club) and I have tried everything from those threads. They are usually ancient, and nothing ever seems to be resolved about this problem.. so here it is:

M42 stutters when it hits 5k RPM. It acts just as though I am hitting the rev limiter.. except I lose power and my tach jumps.. it will keep doing this until my car starts dropping in RPM. I am completely stumped.

Here is a link to a video that I've made: http://www.youtube.com/watch?v=bPNIZQ5kn3w

Here is a pretty complete and up-to-date list of what I have done to the car that would affect engine performance:

Mods:
Mark D 93 Octane Chip
K&N Air Filter

Maintenance:
New Throttle Cable (149,000 - June 2011)
New Camshaft Position Sensor (149,000 - June, 2011)
New Bosch O2 Sensor (February 2011)
New Fuel Filter (July 2010)
New Timing Chain Tensioner (March 2010)
New 4-Pintle Bosch Fuel Injectors [Part #:0 280 155 710] (September 2010)
New OEM Bosch Spark Plugs (September 2010)
New HQ Autosport Coil On Plug Kit (September 2010)
Fixed the "Mess Under The Intake" (September 2010)

I am running 93 Octane fuel.. always have. No hoses are getting crushed and everything is hooked up properly. Still have not replaced fuel pump, but I don't see why that should be a problem.. never have had a problem with fuel pressure.

Anyone? Ideas? HALP!

[DesktopDave]

It's not much help, but do a stomp test to see what the car thinks is wrong.  I'm not really that good at this sort of thing so I just chase down "what it isn't" first.

Is there any way you can test if it's rich or lean in the midrange?  Tach jumping might be a pointer to the problem.  If the tach isn't reading right (that's a direct signal from the DME) maybe the cam or crank angle sensor is losing sync.  The DME will go to fail-safe mode and kill timing advance.  You lose power and the car stutters.  That might explain it.

I'd suspect the AFM first, then maybe the FPR or pump, then maybe the crank signal or the DME coolant temp sensor.  Test & eliminate, it might be more than one thing.

[Bimmer805]

hmm i dont know if this might be much help but have u tried going back to the stock chip to see if it will cure your problem?

[Brian318is]

hmm i dont know if this might be much help but have u tried going back to the stock chip to see if it will cure your problem?

Thanks for the replies guys.

I'm going to start with AFM and go from there. Unfortunately, I don't have a stock m42 chip.. car came with a Dinan chip and I bought a Mark D 93 octane chip.. sold the Dinan chip.

[DesktopDave]

I have a spare floating around.  It's in a damaged DME though.  Let me know; I'll pull it out & send it along if you'd like to use it for troubleshooting.

I don't think it's the chip - MarkD is a legend for his tunes.  I'll bet it's a sensor causing the chip to make some fueling trouble for you.

[monty23psk]

Here is a wild shot, check the coding plug on the instrument cluster to make sure you have the correct one for you car. You will need jto remove the cluster bezel to look at it. It deals wit the cluster RPM readings but not sure if it tells the ECU something. Really wild guess but check it out. Plug is 62111394321.

Did this issue start recently or since you got the car? I do know those plugs can go bad. Maybe you have a friend with an m42. I see you are in FL, you close to Miami?

[Wizard]

Damn Alex, you beat me to it..I was thinking coding plug also.
And also Dave has some good points. You can check the CPS (Crank) with an ohm meter. LINK:
http://www.m42club.com/forums/showpost.php?p=47711&postcount=5
I also believe that you can get the Crank and Cam sensors reversed as the plugs are the same. Check that..
Not sure about a check for the DME temp sensor, but that could also be your problem. I think I had a similar problem with mine years back.
Does it only do it when car is warmed up?

Dan

[Brian318is]

Thanks for all the responses guys.

Ok so, tested the car today at low temperatures... the car revved perfectly and no hesitations at all throughout the range! So, it seems as though it is only doing it when the car is warmed up. I redlined (7,000 RPM) it probably 6-7 times at low temp just to make sure.. and also performed different throttle positions.. the car acted as it should..

So what's that mean?!

[monty23psk]

Mabye ECU temp sender?

[DesktopDave]

That's what I'd be looking at too...DME and and the AFM temp sensors.  Both use the same resistance ranges.  The DME uses them to determine when the motor is warmed up (of course), then leans the fuel mix way down and kicks on the O2 sensor to go into closed-loop mode.

If those sensors aren't working, the DME keeps the car in cold-start mode...you'll be running pig-rich once the motor gets good and hot.

[Brian318is]

Well the motor is definitely getting good and hot, no doubt about it. Temps in my area are 93+ and 70+ humidity.. terribly hot and not helping my problem at all..

I just took the car out for a quick outing.. the car revved beautifully to over 7K RPM until the car hit operating temperatures. The car is getting more than adequate cooling, and I have an old Volvo electric fan on the car, so not sure what is going on exactly.

I am not sure what you mean by DME? Is that the computer?

The exhaust is not smelling rich even under load, just smells like exhaust.. so I am stumped. I usually do not drive my car hard until it is warmed up, which is why this problem is pissing me off! Although, I have noticed a drop in my fuel economy.. (26mpg combined, and I drive like an old lady usually.)

I have my AFM out of the car right now and I'll try and clean it.. it may have sucked in some K&N oil from the filter, which would really piss me off if it did. I am going to try and clean the AFM and get it back in the car, but we'll see..

[DesktopDave]

DME is Bosch's name for the Motronic ECU.  Same difference, that's just what we call it.

I know the car is warming up & the cooling system is working, but if the DME doesn't know that from the two temp sensors you'll get over- or under-fueling.

Don't go crazy on the AFM.  Any cleaning I've done hasn't made much difference on the four-banger.  From what I've seen the M20's & M30's seem to have a lot more trouble with AFM fouling, never been sure why.  If you're worried about the K&N you might want to temporarily replace it with a stock paper filter until you track this down.

[Brian318is]

OK, going to try and swap DME's. It's going to be a while.. have to wait for it to get here. I will keep these posts updated (also posted on r3v) and we will figure this out. Hopefully the knowledge gained from this will help people with similar problems.

[DesktopDave]

Did you test the sensors?  A lot of people blame a DME when it's just a flaky sensor or two.  Cheaper to use a multimeter than swapping parts.

[Brian318is]

Ok so.. still have not been able to figure this out unfortunately. The car is now hitting a wall at 5k hot or cold.

I replaced the AFM, tried a new DME with stock chip (thanks Ryann) and also checked the connection for my o2 sensor.

I have not replaced my crank position sensor.. maybe that could be the culprit?