Hello,

I wrote a ridiculously long thread and then it didn't post so I'll make it as short and sweet as possible.

The truck - '98 12V QC 4x4 5sp

Mileage - 176,000

Repairs since I've owned it - (2) head gaskets, latest a .20 over Cummins marine w/ ARP studs, new Carter lift pump, Rubber supply and return lines down on the frame rail, thermostat.

Symptoms - After the last head gasket replacement the truck came home with no power. It has no guts at all. Unloaded it will lose speed traveling up a grade at 60 mph in 5th gear with the pedal crammed through the floor. No torque rise. Beyond about 1/3 pedal travel there is no more fuel or power to be had, and it almost feels like the pedal hits a hard spot.

Hypothesis - I feel like I'm dealing with some kind of boost loss causing the AFC not to move, and, therefore, not fuel.

Actions Taken - Installed Tork Tek OFV and BD boost orifice (it was laying around waiting on gauges so I tossed it in just to see what happened). I've tightened all the intercooler boots, put a wrench to the intake and horn bolts (they seemed loose, but I didn't look up the torque spec), inspected the AFC boost reference and wastegate actuator lines. Played with the star wheel just to see if it did anything. Cleaned the pre-screen and bowl (it wasn't dirty).

Results - OFV seemed to help a little (certainly needed it anyway). Boost orifice lit the turbo a couple hundred RPMs sooner, but made no real difference in the power. The star wheel did absolutely nothing. It is plum up under the housing and the truck doesn't even puff smoke (except for some oil smoke the first time you take off after startup).


Planned Actions - I would like to pressurize the system to check the piping, boots, intercooler, intake, AFC, and wastegate actuator for leaks. I also need to isolate the AFC and wastegate actuator with regulated air to check function. I've wanted them for years and I'll be installing pyro, boost, and fuel pressure gauges as soon as the weather warms.

Thoughts - I've been very focused on a boost leak causing the afc not to move, but the fact that cranking the star wheel so far forward didn't result in quite a bit of smoke pre-boost has me thinking fuel might be the root cause. I hope not. I change fuel filters every 10,000 miles and the lift pump was new about 30,000 miles ago which leaves the injection pump as a culprit.

Let me know what you all think might be my problem. I don't have to drive the truck daily any more so it is set to become my toy, but I don't want to start modifying a sick truck. I want to have a plan of action in place so that when the weather breaks I can get to work on it.

Thanks in advance for your help.

Regards,

D.P.

 

Alright if you think its a boost leak,Take the AFC housing off and have someone watch the AFC arm while you are in the truck making some boost and the AFC arm will move a tad and if not found your problem!

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Also

 

I'm leaning on the thought that your waste gate could be too tight or is not moving and your not building enough boost to make any more fuel open up ...

Stuck rack in the IP/afc would also do the same thing ... 180 engine ?
What fuel pressure do you see @ idle ?

 

Thank you for the replies.

12VCumminsPower7 - I wasn't aware you could run the engine with the AFC housing off and the pump opened up like that. I might give it a try, but I was planning to check the function with regulated shop air anyway.

4x4manonbroke - The wastegate has been a primary suspect. I plan on function testing it with shop air to see if I get any movement or if the diaghphram is cracked. If I grab the actuator rod with channel locks I can't move it. That being said, I don't know how strong 20 psi inside a little canister is. Please explain "wastegate too tight"? Are you meaning that the rod could have been adjusted too long holding the wastegate partially open at idle? I don't believe the wastegate was disassembled during the head gasket swap. I'm pretty sure my guy just removed the manifold and turbo all together and sat it to the side. I feel like the more likely scenario (if the wastegate turns out to be part of the problem) is that the diaphragm has cracked letting the boost signal from the AFC leak out. Either that or the wastegate is seized partially open. I basically stopped driving the truck daily and it sat for several months. If the wastegate won't move with shop air I guess I'll remove the turbo and see if the wastegate can be freed up.

It is a 215 pump.

I wish I knew. I'll have gauges within the next month or so. I can confirm pressure then. Whatever it is, it certainly improved when I changed the OFV. You could definitely tell it ran smoother and picked up off the bottom end better.

Keep the suggestions flowing. As weather permits I'll be trouble shooting some of these various scenarios and reporting back on the findings.

Thanks again,

DP