Weird rev limiter issue.

[Petro]

Finally got around to putting an engine together for my 08 that cracked a piston in early 2021. Bored the block. 020 over, rcd stage 2 cam, 72mm low pressure, stock injectors, stock pump, mini max etc etc. Buttoned it up almost a month ago, truck runs great. No codes, no leaks, runs very smooth. Here's the issue, the truck has what I can best describe as a rev limiter at 3200 to 3800. The more aggressive you are on the throttle, the sooner it hits a limiter. This is driving or free revving, doesn't matter. If I stab thr throttle very hard, it will bounce off 3200 just like a factory limiter. If I'm more gentle with the throttle and slowly ease into it, it will spin 4k as intended. Occasionally it won't do this at all but it happens almost every time I get on the throttle. What's also odd is every time it bounces on this "rev limiter" the battery light comes on. It also turns off my cruise control, soo if I go to hit resume, my cruise doesn't work until I push the on button again. Things over gone over. Batteries are brand new and hold a constant 14 volts all the time according to my minimal and my snap-on scanner. Connections are all clean. Checked them multiple times. When it does this rail pressure drops but according to my snap on scanner it's commanded. The pump holds a solid 24k in my street tune, falls off a little in my big tune but this issue is apparent in even the stock tune soo I'm sure it's not a pump issue. It never throws a code of any sort. I tried retuning, made no difference. These are also the tunes I had before the truck blew up initially and it ran flawless before. Soo sorry for the long post, tried to cover about everything. Let me know if anyone has any ideas because I'm out of them. I work on a large amount of these and have never seen or heard of this issue soo hopefully one of you has some ideas or insight.

 

[Powerstroke Cowboy]

Bad maps sensor?

 

[Petro]

Bad maps sensor?

Boost reads correctly. Not sure how that would affect it while free revving with no load on the engine. Would also assume it would throw a code

 

[Powerstroke Cowboy]

Boost reads correctly. Not sure how that would affect it while free revving with no load on the engine. Would also assume it would throw a code

Olay. I've heard of them breaking and under full throttle it messes things up.

 

[Petro]

If it acted up while driving normally I'd say it's a possibility but the truck runs and drives 100% perfect until you try to get it over 3200 rpm while driving more aggressive. To be honest, nobody would ever know it has an issue until you stomp on the gas. Even in 4th or 5th gear the problem is non existent at wide open throttle because it never reaches 3200 rpm. It pulls hard and runs great making 53+ psi of boost.

 

[lincolnlocker]

Tpms and maps might not be jiving well.. pscowboy isnt wrong... but that is still a tough one to track down....

 

[lincolnlocker]

If it acted up while driving normally I'd say it's a possibility but the truck runs and drives 100% perfect until you try to get it over 3200 rpm while driving more aggressive. To be honest, nobody would ever know it has an issue until you stomp on the gas. Even in 4th or 5th gear the problem is non existent at wide open throttle because it never reaches 3200 rpm. It pulls hard and runs great making 53+ psi of boost.

Tuning could be wonky as well

 

[Powerstroke Cowboy]

If it acted up while driving normally I'd say it's a possibility but the truck runs and drives 100% perfect until you try to get it over 3200 rpm while driving more aggressive. To be honest, nobody would ever know it has an issue until you stomp on the gas. Even in 4th or 5th gear the problem is non existent at wide open throttle because it never reaches 3200 rpm. It pulls hard and runs great making 53+ psi of boost.

Very interesting. I hope this gets tracked down for you. I really want to know what it is!

 

[Petro]

Tuning could be wonky as well

I'm assuming it's probably not a tuning issue because this is the same tuning it had on it before it popped and it ran flawless before. I only retuned it after I discovered this issue with the new engine installed just to eliminate the possibility. I also reset the adaptive fuel tables to eliminate the possibility of something weird there. This thing cuts fuel soo hard it will damn near throw you forward, but if you don't let off the throttle, it will grab a gear and go right back to pulling hard until it hits 3xxxx or whatever rpm. My thoughts are, if it was a sensor causing it to defuel this hard, it should throw a code or at least say "reduced engine power" and stay in that limp mode. For some reason it just thinks 3200 is where its supposed to limit while heavy on the throttle. I'm leaning toward a possible ECM maybe.

 

[lincolnlocker]

I'm assuming it's probably not a tuning issue because this is the same tuning it had on it before it popped and it ran flawless before. I only retuned it after o discovered this issue with the new engine installed just to eliminate the possibility. I also reset the adaptive fuel tables to eliminate the possibility of something weird there. This thing cuts fuel soo hard it will damn near throw you forward, but if you don't let off the throttle, it will grab a gear and go right back to pulling hard until it hits 3xxxx or whatever rpm. If it was a sensor causing it to defuel this hard, it should throw a code or at least say "reduced engine power" and stay in that limp mode. For some reason it just thinks 3200 is wear its supposed to limit while heavy on the throttle. I'm leaning toward a possible ECM maybe.

They can corrupt. But i understand where you're coming from.

 

[Powerstroke Cowboy]

What would be crazy is if the alternator causing the problems.

 

[Petro]

They can corrupt. But i understand where you're coming from.

Retuned this morning with a whole different platform just for shits and gigs, and the issue is still present. Talked to another buddy this morning who suggested it's a possible cam/crank sync issue. Suggested throwing both sensors at it, soo I may try that today if I can get a lift opened up at the shop. I would assume that would throw a code for as hard as it pulls rail pressure but maybe not.

 

[lincolnlocker]

Thats super wierd

 

[6.0 Tech]

Retuned this morning with a whole different platform just for shits and gigs, and the issue is still present. Talked to another buddy this morning who suggested it's a possible cam/crank sync issue. Suggested throwing both sensors at it, soo I may try that today if I can get a lift opened up at the shop. I would assume that would throw a code for as hard as it pulls rail pressure but maybe not.

I a 6.0 I put a set of bearings in once that I got a tooth off. It had a similar deal, anything above like 2800 or so it would cut out real bad. Also had a 6.4 I had put a crank in that the tone wheel showed up bent, and I didn’t notice it, that would derate and throw an engine oil level overfill code above 3000 or so. Neither one of these was load/throttle dependent though.

My truck is doing a similar thing, where icp is bouncing above 3500, only when it gets a hard pull with the converter locked, worse when spraying. Can tell you so far we’ve pulled icp, thinking the ipr was blowing open, that wasn’t it, and doesn’t apply to you, had a cam sensor take a shit on me, replacing that didn’t fix the cut out, so hopefully you figure yours out, and then I can get mi e figured out. Lol


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[Petro]

Took a video this morning but it wont upload here because its too large I guess. While parked I held the throttle floored and you can see the tach jumping around from 2500 to 3500 rpm and the battery light flickering and the engine sounds like its bouncing on a limiter. The tach doesn't match the rpm. My snap-on scanner actually read zero rpm for a few seconds while this was happening. But allegedly according to the scanner, voltage was a solid 14 volts the entire time, cam and crank sensor had sync, and rail pressure was at a commanded level. No codes what's so ever. Runs flawless when driven normally. I did this at night with the head lights on and the headlights flickered momentarily when the battery light would flicker. So to me that points to a voltage issue but why is it not throwing a single code? Soo ****ing weird.

 

[Petro]

I posted the video on you tube. Here's the link.

 

[lincolnlocker]

Batteries test ok?

 

[Petro]

Batteries test ok?

They're brand new. Haven't load tested them but it whips right over when cranking. After pondering on this most of the morning, I'm going to try a cam and crank sensor. I think the pcm uses engine rpm to gauge what percentage to run the alternator at. Well obviously the pcm is losing the tach signal as shown on my scanner for some reason. Soo if the pcm is seeing zero rpm, it will obviously trip the battery light the same way it does if you're sitting parked with the key on. This also explains why my cruise gets shut off and I have to turn it back on instead of just hitting resume after this happens. The pcm essentially thinks the engine shut down momentarily. My biggest question though is why isn't this throwing a code for either sensor or losing sync?

 

[lincolnlocker]

Holy crap man. Gremlins

 

[Powerstroke Cowboy]

Sounds like you could be on to something.

That things sounds worth than just hitting a rev limiter.