engine and drivetrain M42 Swap Feels Like It Hits Rev Limiter At 4K When Hot

[sbarton]

I got a M42 swapped 1974 2002tii.  After running hard for 30-60 minutes or so, the engine will feel like it is hitting a rev limiter at like 4000-5000rpm or so and gets worse if I keep driving it. 

 

If I let the car cool down it will run fine for a bit. 

 

I've swapped ECU's, coil packs, MAF, even the entire motor with engine wiring harness. 

 

I suspect it is an electrical issue since it only happens when the motor is hot, 

 

 

Any ideas?  Suggestions?

 

-Scott

Edited April 24, 2013 by sbarton

[evol911]

I'm thinking maybe one of the coils is overheating. I have had issues like this in a Honda. Where do have the coil packs mounted?

 

Also might want to check the fuel pump relay and fuel pump.  Fuel pump could be going out.

Edited April 24, 2013 by evol911

[sbarton]

Fuel Pump Relay is part of engine harness and that was swapped with the engine, and still the same problems.  Will try new fuel pump.

 

The coils are mounted in a similar fashion as in the E30.  Up in the side of the firewall.  I replaced the coil packs with a known working coil packs and same thing. 

 

-Scott

[williamggruff]

Scott,

 

Do you have an AFR gauge hooked up to the exhaust?  Jynweythek Engineering ran into the same issue with our Kfish-powered tii, and like Duct Tape Motorsports, we've spent an unfair share of time in the pits trying to diagnose and resolve the issue.  We noted that our AFR went to super lean every time the issue occurred.  Same issue as you've been experiencing: get the car good and hot, and sooner or later it starts acting like we're on the rev limiter.  Like you, we swapped everything EXCEPT the fuel pump trying to sort it out, and we still had the issue at Monticello.  We found that pinching off the return line solved the problem, but I'm convinced that's simply dealing with the symptoms.  We measured fuel pressure on the track at Monticello, and it dropped precipitously when the problem occurred.  Just like your situation, letting the car cool off for a little while in the pits solved the problem until the car got hot again.  Also like your situation, engine temp was not directly correlated with the issue.  I can't imagine your Inka's motor is running way below operating temp for 30 minutes of track time.  I suggest you look at the fuel pump, and note how close your fuel pump is to your exhaust.  In our case, our exhaust exits the car just ahead of the passenger rear wheel, and the fuel pump is located just behind the passenger's rear wheel.  I suspect our bottlecap wheels are drawing hot exhaust across the brake drums (clever), and onto the fuel pump, which helps explain why the problem shoes up after about 3 laps on a hot day, but after an hour or so on a cold day like we had at Monticello.

[sbarton]

Awesome info.  Will take a look at that.  I haven't changed the fuel pump, but just ordered a new one.  Will give it a try.  Our fuel pump is in the rear, next to the fuel cell.  Its kinda in the open air.  Exaust exits on other side before the wheel, so very doubtful it is that. 

Thanks.

 

-Scott

[Inka114]

Scott: Had this problem with our 318, and restricting the return flow from the fuel rail solved our problem also. We suspect it's the pressure regulator on the fuel rail which is causing it. Are you using a typical Bosch pump (i.e the stock early E30 external pump?) If so, check the Bosch literature - that style pump depends on backpressure to properly develop flow, which is what led us to the pressure regulator as the possible villain. This problem only shows up with extended full-throttle operation on track - if the car is only street-driven you'd probably never see it.

 

-Karl (Team Koko)

[williamggruff]

Scott: Had this problem with our 318, and restricting the return flow from the fuel rail solved our problem also. We suspect it's the pressure regulator on the fuel rail which is causing it. Are you using a typical Bosch pump (i.e the stock early E30 external pump?) If so, check the Bosch literature - that style pump depends on backpressure to properly develop flow, which is what led us to the pressure regulator as the possible villain. This problem only shows up with extended full-throttle operation on track - if the car is only street-driven you'd probably never see it.

 

-Karl (Team Koko)

Or this...