Looking for some additional troubleshooting ideas on a problem I'm having.

When cruising at a steady speed with the engine RPM anywhere between 1500 and 2000rpm, you can feel a sort of "hesitation". It always feels like the truck goes to coasting for a second then back to cruising normal. The change is very on and off and a passenger riding along never notices a thing. When it happens, I don't see a change in engine speed, vehicle speed, boost, EGT or anything. But I can feel the difference in the way the truck is running and that things don't match up with where I'm holding my foot on the accelerator. If I get above 2000rpm, I don't notice it. And it seems to happen in any gear (although I usually notice it in 5th when cruising around 45mph).

I've also noticed that at times it doesn't feel as strong when slowly accelerating through that same RPM range (boost at 0psi). Above that range or when getting on it hard, it runs fine. And accelerating above 2000rpm is just as strong as before.

I've tried running with the TST off and the problem is the same. I've set the Smarty back to stock and the problem still exists. Going to try unplugging the TST and going completely stock on the electrical side. I've got the APPS reset procedure, but haven't tried it yet.

Other ideas on things to check or has anyone run into a similar issue? No codes are thrown, been checking regularly with the Smarty and the key trick.

I'm thinking it might be the VP44, but want to rule out other options before throwing a new IP on it.

 

Update...

OK, I completely disconnected the TST this morning and set the ECM back to stock with the Smarty. Went for a test drive and I can't feel the hesitation where I normally can. Hard to tell about power since I went from Smarty/TST back to stock, so everything just feels weak.

So based on the results of that test, I went ahead and loaded Smarty #7 back into the ECM and continued the drive. Everything still feels OK.

So now I'm puzzled...what would cause this issue? When I ran the with the TST connected but off, I had the issue. Now that the TST is off, the problem seems to have disappeared. Being that this is at low boost (and when the TST is off), I'm not sure how the TST could cause this. The only thing that would still be interacting with the truck when the TST is off is the MAP sensor connection.

I checked the MAP voltage with the key off and the reading was inline with normal values.

I'm going to run around the rest of the day with the Smarty on #7 to see if the problem comes back. If not, I guess I'll hook the TST back up and see how things are.

But in the meantime, still looking for any help that anyone can give.

 

Thats exactly what I was feeling before I did the APPS voltage re-calibration, except I threw the P0122 code after I did it. The problem is gone, but the code is still there. I'm willing to bet your voltage is off and its free, so why not give it a try.

 

I'll have to pull it and check out the voltage. Where did you check your voltage at? On the wires coming off the APPS, or at the plug going into the ECM or PCM?

I'm going to run around without the TST hooked up for a few days to see if the problem comes back. If not, the TST is going back on and I'll be double-checking all the connections when it does.

 

You check it at the ECM, the orange wire a blue stripe. Bigblue made a post on the reset procedure.

 

OK, after looking through a bunch of the wiring diagrams, I think I might have found a potential cause for my problem.

In the TST install, the ground wire of the harness is connected to the ground wire in the 9 pin connector to the VP44. This looks to be the same ground circuit used as the ground for the APPS. I'm thinking that when the TST is connected, I'm somehow getting interference on ground signal that causes the voltage seen from the APPS to be slightly off?

Would this be a valid conclusion (been a while since my Electricity/Optics class in college)?

If so, does the TST need to be grounded on this circuit, or can it be connected to any ground (preferably directly on the ground from the battery)?

 

Justin, FWIW - Same place mine it connected with no problems after 4 yrs.
Can't see why it has to be connected there, but don't know. I would call Mark at TST, if it comes back when you reconnect TST?

Quote - AggieJustin -
"I've also noticed that at times it doesn't feel as strong when slowly accelerating through that same RPM range (boost at 0psi)."
Justin, Could this be a difference due to new Turbo? You are aware that TST fueling is activated by boost, right?
IF 0 boost, no TST fueling. I believe the TST comes in at 3 psi on the non Comp PM3. (1 psi on the comp).

RJ

 

I think that was just another symptom of the APPS problem, because I don't have that issue right now running just the Smarty. I had considered the fact that it was possibly the new turbo, but I don't see why I would have just now noticed the problem. It really seemed like it just wasn't trying too hard and now with the TST out of the system, it's working fine again.

I'll find out from TST if it actually has to be connected to that ground, or if it can be tied into any ground. If it can, then I'll probably just ground to a new circuit directly off the battery.

Didn't some Comp users have trouble with boxes before when they weren't grounded well? I'll have to search around.

 

Does not ring any bells. Only thing I recall was some scotchlock issues with VP hook up. I used a Grabber/Banana Clip.
If you have never spoken with Mark Chappel before.... worth trying to catch him. He really knows his stuff!

RJ

 

The more I think about, the more I seem to remember that it was issues making full power due to a bad ground than a bad ground causing other gremlins.

I'll ping TST about the ground connection and see what they say. I'll put the TST back the way it was, but if the problem comes back I'll move the ground to see if that clears it up.

 

Have you tried the APPS voltage recalibration yet? Not to beat a dead dog anymore, but I'm convinced that this is going to help your problem.

 

Not yet, that's the plan for tonight. The g/f is working late, so I have the garage all to myself.

TST is still unhooked and I haven't had an issue with it since it's been off.

 

OK, I did the recalibration on the APPS. My initial reading was .334 and the sticker read .510. I had to rotate the sensor housing as far as I could to make .508. And after I cycled the arm on the APPS a couple of times, the reading dropped back to .490. I adjusted the stop screw a couple of turns and was able to get to .500.

On a test drive it might have been a little crisper than before, but I didn't get fully warmed up to try any hard runs. I just wanted to make sure I had full range on the pedal and no major issues (plus I was trying my 2Low setup).

TST will go back on tomorrow or Thursday after making sure my problem doesn't come back without it.

 

How did it go with the TST hooked up?

RJ

 

TST is going on this afternoon. Had to work late last night, so I didn't get it hooked back up. But all is still going well without it.