Mongo

I'm still tracing down some issues with this car. I took the O2 completely out of the loop on it and have stumbled across an issue whenever I floor it. It seems like at WOT the car has tons of power but will cut out or behave erratically like it's missing. I have checked the ignition wires, coils and cap. Everything is on and fine. Yesterday I got stuck on the side of the road for about 5 minutes after going WOT. After shifting into 3rd gear (car is auto), the engine just completely dropped in power, but was still running and decelerating. No matter how much I stepped on the gas, it was un-responsive. The car's exhaust smelled VERY RICH when this had happened. I couldn't get it started for 5 minutes. When it did start, the car ran completely fine like there was nothing wrong with it, so I took it easy getting back home.


I am suspecting the throttle switch in this issue and maybe a malfunctioning WOT that is still activated when lifting off the throttle. It's like the car is fueling itself when it's not supposed to. I had sent my LH out to Roger and Sean for testing and they confirm that it's functioning correctly. We can rule that one out. Any other ideas where to check next?

I have changed all three major relays also - LH, EZK and Fuel Pump if anyone wants to know. Less than a month old.

AO

A stuck WOT switch could cause it, but it does not explain the drop in power.

My guess is that you have a bad coil, coil wire, or final stage ignition module. This would account for both the loss of power as well as the overly rich (half the fuel would be going out the tail pipe).

Mongo

Are those the ignition modules in the front of the engine just behind the bumper on the driver side?

This only happens at WOT by the way. Normal accelerations are completely fine just as long as WOT is not activated.

AO

Yes, that's what I was referring to.

But let me make sure i understand your symtoms. If you stay out of WOT and slowly bring up the RPMs, it's fine. But if you punch it, power falls off at 4500 RPM. Is this correct?

jcorenman

Andy,

I'm with Andrew on this, sounds like ignition problems.

At high combustion pressure (i.e. WOT) it takes more volts for the spark to jump the sparkplug gap, so any leakage path such as failing insulation will be more likely to arc over and fail. Check the wires carefully especially where they are routed close to the metal belt and cam-covers.

Also check your plug gaps-- larger-than-spec gaps will aggravate failing insulation.

The WOT switch wouldn't do this, all that does is switch the EZK to the WOT map which shifts the timing a bit, and tells the LH to add some extra fuel. So a missing WOT switch would cause it to run a bit leaner, not richer.

Cheers,

Mongo

I posted another thread yesterday Merlin was helping me with. The engine was pretty much revving itself in the driveway yesterday which also makes me suspect the TPS. I figured that was just a binding cable till now. Andrew you are correct in your understanding. If I stay out of WOT it will not be symptomatic.

AO

If your having multiple problems, keep them in the same thread. You know better than to separate the symptoms into multiple threads as they could be inter-related.

I could see how a false air leak, could cause the reving symptoms. I also have had a frayed throttle cable that caused this, but I still had plenty of power (actually too much!)

So I think these could be un-related. A bad coil/final stage ignition module would not cause the "self revving" you described. I would get that one fixed first, then move on to the lack up top-end power.

blitz928

Does the engine rev over 4500 Rpm freely when the car is in park or neutral? Are these symptoms only happening while driving?

Mongo

Revs fine all the way up the dial. Just when driving if I hammer the pedal to the floor and touch the kickdown switch the car lost power after 4500.

blitz928

Sounds like what happened to me..But you have a new LH...

https://rennlist.com/forums/928-foru...h-andrade.html

Mongo

Yup and it's been confirmed that the new one is fine. I still think it may be the TPS. I have heard new ones going bad before; it's not that I have my heart set on this, but if a car revs by itself and then a WOT switch sticks, floods the engine and kills it, it sure does make a fine suspect.

I would like to test the ignition modules that Andrew mentions above prior to replacing them. Is there a procedure to test with a multimeter?

Andrew - I forgot to mention that the coils and ignition wires have been replaced also very recently. Also, what is the estimated life on these ignition modules in the front of the engine?



Something tells me that all the prior problems with the O2 loop may actually have not been the O2, but rather something else. The car is ROW coded right now and I have an AFR gauge hooked up to a universal O2 for reading. I did catch a glimpse at the LEDs lit in the rich field when the power drop occurred. Amazing how the sucker just fired up fine after 5 minutes and drove home..

RET

I can't see how this would be related to the other problems, but loss of power at higher RPM under load and with WOT might be caused by a fuel delivery problem. Precisely the situation I had with a failing fuel pump on my old MBZ: it could not supply the needed volume. FWIW, it's easy enough to check pressure and volume per the WSM.

Good luck.

Bob

Mongo

Hey Bob,

I don't think it's a lack of fueling at WOT that is the issue. It is actually over-fueling the car. When I mentioned the power loss, it was like the engine literally cut out, or like the gas pedal cable broke and there was zero throttle modulation related to engine speed, hence the engine decelerating. With that being said, the cables are fine though.


This may be something electrical, but I just have no clue what else to test. Every sensor passes with an ohmmeter.

mark kibort

arcing in from the low voltage to high voltage part of the coil will do this exact same phenom.

Mongo

What would cause the arc? Everything is new there and no exposed wires..


I'm not going to SATP this weekend as I'll be figuring this crap out. Getting REALLY close to selling it as is...