High Compression M20 problem

[Fernflex]

I have been building my car for a year, I have a problem with the engine.

If I accelerate the engine it limits at 5k rpm, I already tried 4 different ecu, checked the tank fuel pump, replace fuel filter, try 2 different fpr, it has new sparks plugs and cables from Ireland when I was going to try another crank sensor I notice the harness coming from the car that connects to the sensor is damaged can that be the problem? anyway I installed the new crank sensor and it did the same thing!

The car idles is good considering the big valves, 288 cam, msd 6al, msd ignition coil, ireland spark plugs cables, I pistons and block, E crank and rods.

I also swap the afm!

Im guessing it can be the damage cable, maybe the car timing is wrong or the spark plugs cables are in the wrong order

:drink:

[Sagaris]

check to see the exact rpm it starts having a problem, if it is at 4500 rpm and above then that means the problem only happens during open loop and that can narrow things down a bit.

[Fernflex]

I think it is because below 4000-4500 the car works perfectly.

What is open loop?

[Sagaris]

"Open loop" is when the ECU ignores sensors like the oxygen sensor and airflow meter and determines an appropriate ignition timing and fuel mixture (see also injector pulse width) based on RPM, and possibly engine temperature or some other factor. The car does this while it is cold since the oxygen sensor needs to warm up to work properly. Once warmed up, the ECU switches to "closed loop" and uses the airflow meter as well as the oxygen sensor to determine timing and fuel. This fuel system is also designed to run in open loop after 4500 rpm, I am not entirely sure why but perhaps the change in fueling occurs too slowly for those high rpms when the engine is listening to the AFM and O2 sensor, thats just my suspicion.

If it really is 4500 rpm exactly when things start to run bad then it would seem that something relating to how the ECU runs open loop is wrong.

I have never heard of a case where the car was running badly at high rpm and it wasnt a fuel pressure issue.

Typically the problem is the opposite of yours, to where the car runs like garbage up until 4500, THEN when it switches to open loop the car runs great. That problem indicates that the oxygen sensor is bad since the car runs better as soon as the ECU ignores it.

Do you have an adjustable cam gear by chance? perhaps the cam timing is off

As for the crank sensor, your car will not run at all if that is bad. So I do not think a bad crank sensor is your problem.

[morerevsm3]

I had exactly the same problem, it is the harness connector under the inlet manifold and/or corroded wires in that area

[BMC227]

Check your harmonic balancer, could be out of line or bent. A friend had the exact same issue with his 325is

[Luis325]

Yeah the car starts to missfire right when it hits open loop....
And we have checked almost everything on the car...you hit WOT and the car opens real good up to 4to5k then starts to boggle and missfire...

Please help us... Ferflex want to kill the car with a baseball bat..
and we dont call him "angry elf" for nothing.........:blowup:

[Sagaris]

Haha^ BMC made an excellent suggestion which coincides with an open loop-only problem. If the toothed portion of the harmonic balancer which the crank position sensor reads is wobbling or loose, it is very possible that at a certan rpm the harmonic balancer hits its natural frequency and vibrates enough for the car to miss the timing data from the crank position sensor. I would visually check the toothed portion of the harmonic balancer while reving the engine to see if it moves at all. If it is hard to see and you have a timing light which has the timing advance adjustment dial on it, you could point the light at the harmonic balancer and adjust the dial to see if the balancer changes position (let me know if that makes absolutely no sense) hopefully it is easy enough to see on its own.

You might also try connecting an ohm-meter in series with the crank position sensor while keeping the sensor plugged into the car if you can figure out a good way to do that, then watch the resistance as the car gets around the bad RPM range and see if the resistance goes to zero.


Also dont forget to check the full throttle switch on the throttle position sensor. If the switch is bad, then the full throttle fuel enrichment is not present and the engine is starving for fuel up top then that could contribute however I have never actually heard of that happening in real life, it is just a thought.

[Luis325]

Heres a few Videos of what the car is doing!

http://s150.photobucket.com/albums/s93/luiscaratinijr/?action=view&current=a593aefe.mp4

http://s150.photobucket.com/albums/s93/luiscaratinijr/?action=view&current=574a4e35.mp4

Pics of the harness plug where the crank sensor connects too... This is what we are guessing????

[nando]

99% it's the crank sensor.

classic sync loss issue, the shield is damaged and causing noisy timing pulses to be sent to the ECU. it can handle some amount of noise but as the RPM climbs it gets worse due to how VR sensors work. ECU loses the RPM, shuts off fuel and you have your mystery rev limiter..

[Luis325]

The crank sensor was changed to a new one.. the harness plug is the one pictured... Nando
Can i splice it and put another one?
Or fix this one? Electric tape? LOL

[nando]

you can probably fix it, the frayed part is the shield ground, it needs to be reconnected to the proper pin on the connector. if you pull the boot off you'll probably see where it broke.

[Luis325]

FIXED IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Uploading video!!!

Thanks guys!

[Luis325]

First Burnout!

http://s150.photobucket.com/albums/s93/luiscaratinijr/?action=view&current=5a784c76.mp4

[Luis325]

Fern still need to do allot of thing to the car.. But it runs really well!'
Fast and fun!!!

http://s150.photobucket.com/albums/s93/luiscaratinijr/?action=view&current=5deac5ac.mp4