Wont rev past 2000 rpm

[badburban]

I have done a search on this and found several different fixes and I've already done some of them, so I'm looking/hoping for some advice or guidance from the experts on here on where I should go from here.

The truck (04.5 LLY GMC) will drive along fine until i put any sort of heavy fuel load on it (WOT, pulling up hills, etc) and then all of sudden Ill only be able to hold 2000 rpm and if you try to run it past it will surge, obviously Im bumping up against a pcm imposed limit. A shutdown and restart after a couple minutes seems to reset it for a little bit, but today I had to make a 90 min trip and had to pull over 5 times to reset it (rather annoying). Now it has been doing this for several months and has progressively gotten worse and worse.

From what I've searched heres what I've found as problems

1) Injector Connectors - I already replaced when it started running ROUGH and had no power a few months ago
2) Lift Pump - Installed one to no avail, actually almost seems worse
3) Fuel Filter - Did this before and after fuel filter changes but I have a new one I'm going to install
4) Injectors - need to check injector return rates somehow
5) Lift Pump - dont have a way to see commanded vs actual rail pressure, will have to wait till Im back in MI and have a buddy hook up to it with his Tech2.

Do you guys have any suggestions? Thanks.

Josh

[Duramaster]

Yeah, here is one. Next time this problem occurs and you have a GM Tech2 with you, observe the actual vs. desired fuel rail pressure. They should be real close. If there is a huge difference lets say like desired is 20k PSI and the actual is 10k PSI and all filters are good and you don't have a GAS cap in place of the DIESEL fuel cap, then you could possibly have a defective FUEL RAIL PRESSURE LIMITER VALVE. I have not come across this for quite some time, but I have run into this. It is part of the left fuel rail but is available separately for about $350 I think :confused: ? Anyway, this is a possibility. Also, have you checked the fuel cooler to make sure that it is not plugged with dirt and debris? :)

[badburban]

Duramaster,

OK thanks for the advice I'll have to check that.

Josh

[mark45678]

could also be sucking air into the fuel system ?

[badburban]

So I had some even worse problems on Friday driving back to Detroit, no way to reset and get over 2k even had a hard time struggling to get that far. So since I was back in Detroit, I had my buddy hook up the tech 2 to it. Well despite the fact I had no SES light on I had a code for Low Fuel Pressure under Power Enrichment. So at idle he could crank up injection pressure at idle with the tech 2 and it would go right on up to 25k psi. Under an extremely light accel (<1800 rpm) it would build pressure, but under a light accel reving to 2300 rpm (could only do this once after a long shut down) for shifts, it would hit ~2100 rpm and commanded fp would be ~20k+ psi and it would fall to less then 10k psi. It could make pressure, but it couldnt supply any sort of volume of fuel and keep pressure. Based on that I'm guessing its not the FPR or the Fuel Rail Pressure Limiter Valve (junction block) since I can defintely build pressure at idle when commanded with the tech 2, but anytime any sort of fuel volume is required it can't handle it. So Im lead to believe its the injection pump. Do you Dmax experts agree with my diagnosis.

Ok so now my next question is, is there any difference b/t the cummins cp3 and the dmax cp3. Also do any of you know good places to pick up a CP3 or especially a modified CP3 for reasonable prices. Thanks Alot guys.

Josh

[Duramaster]

From experience, I would still call it a defective Fuel Rail Pressue Limiter Valve. And there is no JUNCTION block on the LLY. The limiter is located in the back of the LEFT FUEL RAIL. ;)

[badburban]

Duramaster,

Thanks for the advice. I guess I just called it the the "junction" since there are several lines. I know right where it is, I was chasing down fuel leaks a while back. I know when we looked at the FRP values at idle it was ~1100mm^3 and the most we saw was ~8000mm^3. My buddy jumped on the gm tech site and we looked at the GM troubleshooting list and our FRP values were below the max (I want to say 15,000mm^3 max comes to mind but I could be off). Now I'm not saying that its still not bad. Is there anyway to troubleshoot/single out the FRP? I just thought that since it was more fuel volume related and when no/little additional fuel volume is required it can hold pressure no problem. Id be interested in knowing if I can single one or the other out (obviously don't have extra money to spend). Thanks for the help.

Josh

[Duramaster]

So a down and dirty way to verify that the FRP limiter is the cause is to remove the little rubber hose from the rail and pinch it off so it won't leak. Then run a clear line onto the nipple of the rail into a clear bottle. Next is to duplicat the problem. I usually ramp up the fuel pressure and then stab the throttle a few times to get it to act up. There should be NO fuel leaking from the limiter at anytime. I forgot what the limiter is set to, but the FRP should NEVER reach the limiter pressure at anytime! I believe it is around 30,000 PSI or so. There is no print in GM SI. I have only heard this from GM TAC and that was over a year ago. That tells you how often I have to deal with this issue (not very). Anyway, lots of luck. Keep me posted. ;)