Odd Issue at WOT: S-Eta

[TFJR]

Hi All,
I'm trying to diagnose an odd issue I'm experiencing at wide open throttle on my car. Just some quick background on the car:

'88 325 SuperETA - auto with a S3.73. New t-belt, water pump, belts, all tune up components, no vacuum leaks, new throttle position sensor about 2k miles ago. No oil leaks - overall the car runs really well.

ISSUE: After letting the car fully warm up, when I go full throttle/wide open throttle, the car will choke about 2 seconds later (usually after kicking down at least one gear), the engine will literally shut off (zero rpms on the tach), warning lights on the cluster, then all of a sudden come back to life. Once the car comes back to life, I am free to go WOT as many times as I like without experiencing the same issue. This started developing about a month ago.

Yesterday, I "tested it" again, this time after trying to catch a light after some idiotic Seattle pedestrian was slowly jay walking. I leaned into full throttle from a stop. Once it approached ~3,800rpms it died again, this time however it shut off for about 8-10 seconds before coming back to life. I also noticed a not so wonderful mechanical smell. It wasn't strong, and didn't last long, but thought it worth noting.

A friend thinks it may be the cam sensor, however I would think it would be every time I'd go full throttle, not just the first time on a drive. He also thinks it may be a fault in my 153 DME ECU. I have a 173 ECU I could throw in to test, but I'm not sold on the diagnosis.

Any thoughts from the R3V community? So far it hasn't left me stranded or left for broke, but anytime I do want to utilize all the cars power, I am mentally debating it in the back of my head.

Thanks all for any insight!

[cheffy30]

so you step on the gas from at stop it hits 3800k and dies for a few seconds and then comes right back? that is so weird man... maybe its a malfunction in the airbox?

[TFJR]

so you step on the gas from at stop it hits 3800k and dies for a few seconds and then comes right back? that is so weird man... maybe its a malfunction in the airbox?

The only time I usually floor the car is on the highway to get around some deadbeat hogging the left lane. Yesterday this was from a stop, and I gradually floored it. I was probably going 25-30mph when it shut off. Usually its more at 60-70. Only on full throttle.

[MrBurgundy]

There is no cam sensor on your car. But, if you're seeing the tac hit 0 and the car springs back to life without having to turn the key, I'd definitely test the crank position sensor.

[cheffy30]

The only time I usually floor the car is on the highway to get around some deadbeat hogging the left lane. Yesterday this was from a stop, and I gradually floored it. I was probably going 25-30mph when it shut off. Usually its more at 60-70. Only on full throttle.

faulty floor switch maybe.... bad connection down there from too many stomp tests? just thinking...

sent via carrier pigeon launched from the trunk of my daily e30

[TFJR]

There is no cam sensor on your car. But, if you're seeing the tac hit 0 and the car springs back to life without having to turn the key, I'd definitely test the crank position sensor.

Thank you - yes you're 100% correct. I meant to write crank sensor in my original post, not cam. I will go about ordering a new one to see if it clears up the issue as you're the 2nd person with the same hypothesis.

[MrBurgundy]

There is a resistance test that you can perform before you order one. Just to make sure that’s the problem.


Sent from my iPhone using Tapatalk

[Gregs///M]

These symptoms can also be caused by a faulty AFM, air flow meter. When you AFM reports poor feedback, it will trick the DME into thinking its getting very little air. This will result is reducing the fuel output and you experience sudden and brief power loss. See my thread on AFM's for more info how and why this occurs.

[tomstin]

Could the fuel pump be picking up junk in the tank?

[Kershaw]

Check/replace your main relay?

[TFJR]

These symptoms can also be caused by a faulty AFM, air flow meter. When you AFM reports poor feedback, it will trick the DME into thinking its getting very little air. This will result is reducing the fuel output and you experience sudden and brief power loss. See my thread on AFM's for more info how and why this occurs.

Great call. This was my hypothesis. I'd love to send mine down to you (as well as the spare "i" cluster I have that needs a refurb). If the crank position sensor tests out OK this is where I'll move to next

Could the fuel pump be picking up junk in the tank?

Possibly, I'm replacing the fuel filter this weekend so I'll see if there is any build up or deposits. I have run the car probably 3500 miles in the past 4 months, all 92 top tier octane however so I'd be surprised if it is the culprit. Definitely haven't ruled that one out!

Check/replace your main relay?

Relay was tested and is in good shape.

[tomstin]

Possibly, I'm replacing the fuel filter this weekend so I'll see if there is any build up or deposits. I have run the car probably 3500 miles in the past 4 months, all 92 top tier octane however so I'd be surprised if it is the culprit. Definitely haven't ruled that one out!.

I've seen some strange symptoms where the junk in the tank is getting sucked up into the pre-filter at the base of the pump inside the tank. Starves the pump for fuel. Once the volume demand drops, so does the trash. The only way to confirm is to open the tank access, pull the pump out of the tank and see what junk may be in the tank. Best done with the tank VERY low on fuel.

[TFJR]

Well, bad news. The problem is still prevelant and I'm at a complete loss. Here's what I've done. I'd love suggestions on what to check next. I'll be bringing the car back to my shop that knows E30's much better than me. They're starting to feel stumped as well.

- Replaced my crank position sensor which was out of spec
- Fuel filter was actually recently replaced and is brand new so I know that is not the culprit
- Swapped in a good known AFM from another M20
- Swapped out my ECU (it was a 173) with another Bosch 173

At first go this morning after letting the car fully warm up I pinned the throttle and the car laid down two nice fat strips of rubber! The next time however once I hit about ~3800rpms the engine cut out, shut off and then instantly came back on. I'm at a loss. The entire ignition system is in great shape as well.

[AndrewBird]

Do super etas have the extra reference sensor on the bell housing of the transmission? Maybe that's gone bad?