Hey all, I've already kind of started this discussion elsewhere but I thought I might start a separate thread and hopefully you all can help me diagnose this issue.

The issue that I am having is that my new truck just seems sluggish for some reason. It starts and runs fine (needs new GP's but that is a separate issue) but it just seems like it is a real dog when it is first started. Now let me clarify what I mean by that. The truck seems to limit fueling until it has been running for at least 15 minutes or so and then it runs just fine. The odd thing is that it doesn't seem to be temperature related at all, just a matter of how long the truck has been running. It's so bad that I have to really be careful pulling out into traffic unloaded or with an empty trailer. It's almost like the PCM doesn't read anything past about 25% throttle but it wil ltake off like a rocket once you get it above 2500 RPM. My old truck was an auto and would do this for the first 30 seconds or so after it was started first thing in the morning but this one (being a ZF5) drives different. I don't know if I am just lugging the engine way too much or what.

So here is what I know:

• Fuel pressure checks out to about 60-65 PSI at idle (new fuel pump)

• Fuel filter is new

• FPR screen is clean

• New hoses on all fuel system connections around the bowl

• I do think I have a slight boost leak on one of the up-pipes but I can ready 16-18 PSI boost when I tach out the engine when it is warm, so I don't think it is leaking all that badly.
• I know for a fact that the EBPS tube is plugged EBPS reads about 14PSI all the time (I am assuming that it reads absolute value and that is atmosphere? My other truck does the same thing)
• EBPV is unhooked and wired open.
• No cat.
• I was able to borrow an Aeroforce Scangauge and scan some data while driving and the EOT sensor works, but the issue does not seem to be EOT related at all it does this whether it reads 60* or 185* and my old truck fuels harder at 60* EOT than this one does.
• MAP sensor reads good pressure (that's where the boost readings are coming from -- no gauges yet).
• Issue does not change by unplugging the MAP sensor.
• ICP reads a pretty solid 675-700 PSI at idle at around 14% Duty Cycle.
• Driving, ICP gets up to about 2600PSI at about 34% DC but wont go above that pressure or DC regardless of what I do.
• The truck does idle a little bit uneven even once it is warm, like you can hear the IPR cycling or something.

I have another truck here to compare this one to (both are 3.55 rear ends) but one is an auto and the other is a manual. This truck drives well and pulls great once it finally gets with the program but this issue bugs me.



A couple questions I have are: does the SG give you the ability to read TPS position in case that sensor is flaking out on me? I do have another TPS I could swap in and try I guess. Does the SG read the BARO sensor? Having heard Oldwoods' issue with is BARO sensor I am wondering if that may be part of or all of the issue. I think I probably have another one of those too. If not I know where I can get a used one to try.



I have or can get just about everything I could need to try and whoop this issue but I am not sure where to start and I am not familiar enough with seeing live data to know if what I am seeing is typical or not.


Any help is much appreciated.

 

You can check the TPS for flat spots with a DVOM .. I would look at what the ICP is reporting to the PCM .. & also pull the IPR & check the small O ring on the end. THe IPR may be the problem too , sticky when cold .

 

Nate - good write up. Lets get this problem licked!

A few points that jump out at me now, but I'll prob have more later. Compared to my numbers (all from a AF interceptor as well), your HPOP seems it may be a bit weak. I want to say my IPR DC is no more than 10% (at ~650psi) even right after cold start. Also, I can hit ~3200 psi at WOT. My IPR DC also maxes out at 34-35% so that seems normal...

Not the best news, but maybe at least partial source of the problem.

Also, the AF does not read BARO direct, but you can do the math to get it. The engine determines boost by finding the difference between MAP and BARO. So if you display MAP and BOOST at the same time, BARO will be the difference. The catch is that like most sensors, if the BARO is bad, the computer just ignores it and uses a default (14.7) in this case. When my BARO was bad, I did get a P107 code, but only AFTER my auto to manual PCM swap - don't ask me why on that one. Also, in hindsight, I noticed that my engine off and idle boost number was often slightly above or below zero when the BARO was bad. With the good one in there, it's a always dead on zero (or maybe .1). Finally, my BARO problem seemed to crop up more often when the truck was warm. Though I only owned the truck from July onward and got it fixed before this cold weather came, so I can't say what it would have done in the winter.

Anyway, maybe that HPOP is worth a look. You know this, but a good test there would be to take the same readings with BRAND NEW oil. The thicker oil should lead to lower IPR DC at idle and higher max ICP, right. A good HPOP shouldn't really see much of a difference, I'd think.

However, I don't see how a weak HPOP would cause your symptoms. I'd think power would get worse instead of better as engine temp increases - and oil thins.

I think I mentioned that my truck (with 355k miles) is similarly sluggish at startup. I think I've just written it off as old injectors. I have no idea if they're original or not, but in this cold weather, I get steady smoke at startup. I def have a few bad GPs, but it starts pretty well, so prob not more than 2 or 3 out. Anyway, the smoke seems to go away as power comes up, leading me to believe poor atomization is at least part of the problem...

 

Thanks for the input guys. That gives me a place to start.

 

Just edited my post with some additional thoughts, but looks like you we're posting at the same time...

 

Yeah, it looks that way.

The oil is new (less than 100 miles on the last oil change with fresh Rotella).

Rick, I can check the TPS with a DVOM that's true but somehow I doubt I could be that lucky. I may do that just for kicks though. Is there another way to verify the ICP readings I am seeing on the Scangauge? Maybe I'm confused because I thought that was what the PCM is seeing. So is the maximum value for the IPR 34-35%? I thought it would go up to 45% if needed.

 

I'd try the ICP from your other truck and see if it changes on the SG.

 

My icp has never exceeded 35 on either truck I've monitored. I just figured that was normal for stock engines. Sure leaves a lot of room for tuning though. :-)

 

I may be wrong, but it seems like you should be getting more than 2600 psi though. Is it that same when it takes off and starts running good?

 

Honestly the amount of driving I have done withe the SG on it has been limited so far and it never really straightened out when I was driving it this last time. It pulls great up top, it is just really gutless down low. And yes, the 2600 PSI seems to be as high as it would go all the way through the RPM range, but it never really straightened out and ran like it should. I know it surprised me when I got in the old truck and it would make 3,000PSI when it was cold though. Maybe I will swap ICP's and see if that makes any difference. It's an easy thing to try anyway.

I may swap ICP's and see if it makes any difference. I better do it soon because I think I've got a live one on the line for the old truck, lol. It may be gone by this time next week (hopefully).

 

How many miles on it Nate? If a lot of miles then I feel its your injectors.

 

201,000 miles on this one Glenn. I'm not going to say it has been well maintained, but I can't see it being injectors when the ICP is as low as it is. Unless the injectors are just shot and bypassing too much oil internally, but I would think it would smoke and use oil if that were the case and it does neither. It runs smooth too, the injectors in it sound as good or better than any of the other PSD's I have driven.

Oh I see what this is, lol. One guy says injectors, one guy says HPOP.

Who wants to tell me I need e-fuel and a chip?

Maybe it's my old exhaust system causing too much back pressure, better replace that too, just for good measure, lol.

Seriously though, I do appreciate the help guys.

 

Seriously though, give it a drink of PS.

 

Following along for learning purposes. Sorry Nate, I have no input because I simply don't know enough yet about this issue. I will say this. The '97 I owned some years ago would act up like this on cold start ups, and that was living in Colorado. It would not even get out if its own way and then all of the sudden would lurch forward and take off like someone gave it a shot of nitrous. I found out it was the EBPV sticking closed at warm up. You said yours is wired open though, so I highly doubt that has anything to do with it. I was just wondering because that truck would do the exact same thing and run great when warmed up or in higher rpm's when it was cold. Anyways, back to the issue....

 

I haven't done that to this truck yet, but I have done it a couple times with the old truck using Lucas fuel treatment. I have a buddy that works on a bunch of these International engines (he's a mechanic for UPS) and he says that when they start smoking and misbehaving they take them out and get them warmed up, shut them off, drain the fuel bowl, fill it with Lucas, Start the truck up and give it the beans! He said they lay into them and watch the smoke roll, lol. He claims it does a lot for cleaning up the injectors, clearing out the valves, etc. Like i said, I've done it with the old truck and it seemed to help.

I probably do need to give this one the same treatment, but I doubt that will affect the numbers I'm seeing with the ICP and IPR.