M20B29 hesitation at WOT above 5k

[Slicktop_serg]

Cap and rotor?

Have you checked the cap and rotor? i had the same issue after changing bunch of parts like fuel pump, plugs, wires, coil,vaccum lines, etc changed it all and still had issue changed cap and rotor and she drives like a bat outta hell.

[sert57]

brand new bremi cap / rotor / plug that seem to work fine at all rpm at partial throttle and up to 5k at WOT.

Applied some dielectric grease to the C191 connector and that didn't change anything.

While sitting in a parking lot i had a friend hold the engine around 4k rpm and i wiggled the connectors for each injector but couldn't get any issue to pop up

Hooked up a wideband AFR. At the problem area the mixture leans out instantly ,so much, it maxes out the gauge ( using an AEM setup, so > 18).

This seems to rule out ignition system and point towards an electrical gremlin.
In thinking either CPS signal as previously noted. I may look into some simple emf shielding next to see if I can get any change.

The issue isn't consistent in terms of what rpm it hesitates at each time, but its always above 5k.

[digger]

What is the afr like immediately prior to the issue ? Ignition issues can show up as lean.

[sert57]

I was finally able to get a good video of the issue. AFR is in the lower right corner. You can see it run fine until about 5k when it leans out very suddenly.

[Kershaw]

It's too bad you can't swap out another chip/dme. Did you ever try to run it on the stock motronic? Since you have AFR, maybe try it and see if it has the same issue? I would back off pretty quickly if I hit 15.9+ AFR at wot.

[sert57]

I tried the oem chip and it didn't change anything, and have had this chip reflashed once and still no change.

[sert57]

Does the ecu make any sense to have gone bad? It worked fine before the build, but sat in the garage for a few days during the engine removal and install. I may try and find one locally to test.

[sert57]

still running into this, any other ideas?
I feel like one answer is to give up and go standalone, but I'd love to solve it if i can.

[e30davie]

still running into this, any other ideas?
I feel like one answer is to give up and go standalone, but I'd love to solve it if i can.

A mega squirt plug and play ecu is a relatively cheap option and well regarded.

What does the guy say that you bought the "chip" off?

[Kershaw]

https://www.r3vlimited.com/board/showpost.php?p=4474371&postcount=107

Can you move the CPS closer than stock spec?

[sert57]

https://www.r3vlimited.com/board/sho...&postcount=107

Can you move the CPS closer than stock spec?

I tried regapping it a while ago. Originally it was close to 1mm gap and i adjusted it to 0.7 , but it didnt change anything.

That is the first time Ive seen that post, and its VERY interesting to me to hear his results. He is hte first ive heard of moving it out of stock spec to fix the problem. I will definitely try that soon and see what the results are!

[sert57]

regapped the CPS to .4mm - no change
swapped ignition coils with a friend - no change

current suspicions:
1) CPS starting to go bad? It didn't ohm within spec, and it seems like these cars are getting to the point where these fail more and more. its just weird that it works in all other situations.
2) potential bad ground somewhere with the alternator?

I'm not thrilled about dropping $800 + to get this running right with a standalone when it could be a cheap easy fix, but I'm really starting to run out of ideas and am beginning to lean that way.

[apostate]

Check the Vibration damper. With the years it gets soft and in higher RPMs may "confuse" the CPS.
Sorry that I intruded.

[sert57]

Met a guy I knew yesterday who had a Baum CS2000.

First we double checked fuel system, its much easier with 2 people in the car. fuel pressure was good, went to about 50 psi at WOT above 5k. Fuel pump and FPR confirmed good.

CPS signal didn't seem to cut out on the BAUM at all. granted I do not know about refresh rates on this but there was no sign of it acting up.

It seems like theres an ignition issue causing the motronic to cut fuel. Currently suspect of my spark plug wires. When i built my motor I bought these spark plugs from FCP euro, never heard of the brand before. (https://www.fcpeuro.com/products/bmw...i-12121720529a)

Next step if to put known good ignition system from the old B25 on the engine and see if that helps.

[sert57]

Was thinking it may be a grounding issue with the ignition system. Added a ground to the cylinder head but it didn't impact anything.

Picked up a MS2 DIYPNP kit, so I'll be putting that together while trying to troubleshoot this.

Had a friend try his Karyln STI wires vs known good and the Karlyn seemed to be good.