Ideas on what will cause the engine to cut out above 5000 RPM. Sounds like it's hitting a rev limiter, but that is set higher than that. Could it be a fuel pump going out? Simple as a fuel filter? New dist cap, rotor and module. Does it with or without air filter, so air is good. Thanks.
It helps to say what engine you're talking about exactly. The stock 2.8L V6 only makes power to about 4200 RPM, and starts falling flat after that. If you're going over 5000 with that engine, all you're doing is wasting fuel, and putting the engine at risk for damage.
If it is the 2.8 you are probably hitting valve float about there, the iron heads flow poory anyway, and the light valve springs don't help RPM any either. Larry
I had the same problem on my 4.9 but at 4200 rpm.... Are you sure it's at 5000rpm? I ask because my RPM gauge wasn't recalibrated for the V8 and 4500rpm read as 6000 on the gauge... I never did figure it out. Sold the car. Was running too rich so perhaps the fuel pump couldn't keep up...
Yea, I installed the resister on the tach to correct for the v8. But if you were running rich, that's too much fuel. Fuel pump is now pretty much ruled out. The noid light should tell me a lot.
OK, so the noid light blinked correctly at all revs except when it hit 5000 RPM, it got very bright but was flickering as the engine faltered. Really acts like I'm hitting a rev limiter, but it is set around 5500. Rock crawl, any comments on why you picked your rev numbers?
A weak coil could do the same thing......just started happening? Didn't used to do it? I'd check with a known good coil or replace the coil. Be sure to check the button for the rotor as well.
Installed new cap, rotor, coil and module two weeks ago. Ran fine for 7 hour trip after that. Noid light tells me it's an injector signal issue. Doing timing light test as soon as I get back home. May put in old PROM to eliminate Rockcrawl chip potential, but can't imagine how a PROM could change. Radar has a spare ECM I can try if needed. Again, thanks to all for your suggestions and help.
OK, timing light also got very bright and flickered above 5000 RPM, just like the noid light. Checked timing while I was there -- 12 degrees. What does that tell us? I understand that both the ignition and the injection get their pulse timing from the sensor in the distributor.
OK, timing light also got very bright and flickered above 5000 RPM, just like the noid light. Checked timing while I was there -- 12 degrees. What does that tell us? I understand that both the ignition and the injection get their pulse timing from the sensor in the distributor.
That sensor is the pickup coil. Did you replace the entire distributor or just the cap and rotor? If you have a broken magnet next to the pickup coil, it may contribute to your problem also.
[This message has been edited by Gall757 (edited 04-24-2014).]
The ECM get's it's signal from the ICM. So the fact that the ECM is failing to pulse the injectors is only because it is not getting the signal from the ICM correctly, or that the ECM is programmed to alter both the injection and ignition signals at it's RPM cut off.
First thing I would look at is power to the distributor. Does it drop when you are above 5000 RPM? Check right at the distributor. Yes the distributor takes more power when it is putting out more sparks per second. Probe at the red wire where the power comes out of the distributor cap and goes into the ICM module. Does it stay at 14V or drop way down.
Do you still have the old ICM module to swap in to test to see if the problem is coming from it?
Try taking out the Tan/Black wire from the ECM connector (C7). (assuming you know how to without cutting it). This will cause the ICM to run directly on it's own signal and not run thought the ECM. Does the timing light still show the timing cutting out at 5000 RPM? If the timing then isn't cutting out you know the problem is coming from the ECM, and then I would look at if it is really programmed correctly. If the timing light flashes the same then it is not the ECM cutting out the ignition signal.
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The signal comes from the pick up coil. During start up the signal goes directly to the coil control via the circuitry in the ICM. The ICM also sends out the signal via the Purple/White wire to the ECM. The ECM uses that signal to run the injectors.
When the engine is running over 400 RPM the ECM sends a voltage to the ICM on the Tan/Black wire. That tells the ICM to instead of using the pick up signal directly to instead use the ignition signal that the ECM is sending on the White wire. That signal will be advanced from what the ICM sends.
The CAM sensor wiring allows the PCM to know which rotation the crank is on so it knows which injector to fire
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I believe the ECM normally just cuts out fuel at it's RPM cut off but since anytime the engine is above 400 RPM the signal does run through the ECM, the ECM could always do it.
What does the tach do when you have this problem occur?
[This message has been edited by phonedawgz (edited 04-26-2014).]
OK, problem found and fixed. The voltage to the distributor was constant throughout the RPM range, even when stumbling at 5000. Not relevent to the fix, but thought I'd let you know. Turns out that the three wire plastic plug to the ICM had cracked and when I installed the new ICM a few weeks ago, the connections inside the plug did not go all the way onto the ICM tabs. Guess it had worked loose in those few weeks. Once I pushed them home with a little screwdriver, all is back to normal. Again, many thanks to phonedawgz[size=2][/size] for staying with me throughout this troubleshooting process. I really do appreciate your kindness and knowledge.
The problem was not a gentle as your Chevy rev limiter video. It was much more disturbing .. stumbling, missing, that kind of thing. Again, many thanks.
