Log in and log out of VCM Scanner

[Crzna442]

I recently finished up a Gen 4 5.3 / 4L60e swap in a 1979 chev pickup. No modifications to motor or trans. Engine, trans and ecm /tcm were all from the same donor vehicle. I?m having a really strange problem and it seems I might be the only person in the world to run into this because nobody seems to have an answer. I don?t even really know what to search for to help find the answer but I?ve been looking all over the place. It?s like my truck has 2 different modes. One - which we will call the bad mode - where it runs ok but only revs up to about 2400 although shifts through the gears properly - actually runs ok just no power - maybe limp mode but I?m not sure because it still shifts through all the gears. The other mode we?ll call the good mode where everything seems to work perfect and revs up like it should.

Every time I start the truck and drive it is in the bad mode and very rarely it will suddenly switch from bad mode to good mode while driving. I?ve spent countless hours trying all sorts of things to no avail then one day by accident I learned that if I log into the VCM Scanner and log out again it will always 100% of the time switch to the good mode and stay there until I shut the truck off. I can drive for a few hours in the good mode and it will stay that way until I shut the truck off. I can even log back into the scanner and it will still stay in the good mode.

Only changes I have made to the tune is VATS, DOD disable and gear / tire size. Anyone ever run into this before? E38 ecm with tcm that were all original to the engine and trans. Checked and double checked my wiring and it?s all good. Even if it was wiring it shouldn?t change to the good mode every single time I log in and out of the scanner.

[Crzna442]

I?m the only one I guess?

[Crzna442]

Interesting how there is no response whatsoever.

I?ll summarize what?s happening if that helps.

Truck seems to have 2 modes - a mode where it runs perfect and one where it?s not terrible but only revs up to about 2400 and gets there slowly.

When I start the truck it will be in the bad mode every time. If I log into the VCM scanner and log out it will immediately change to the good mode.

I can log back in or stay logged out - doesn?t matter - truck will stay in the good mode until I turn the truck off for about 10 seconds then reverts back to the bad mode.

Then all I have to do is log in and log out again and it?s back to good mode.

No codes - fuel trims are good - MAP is good - MAF is good - everything is good. I just have these 2 modes. I?d like to just have the good mode only.

Has nobody else ever run into this? What is happening when I log out that causes my truck to run better? Someone who understands the ins and outs of HP Tuners must be able to explain how this is possible.

[2xLS1]

Perhaps it's your terminology. You don't log in and log out of the scanner. Do you mean connect to the vehicle and then disconnect with the scanner? Starting and stopping a data log? But to answer your other question I've been using HP Tuners since 2004 on thousands of vehicles and have never run into a situation like you describe. There should be something that shows up in a data log when it's running bad though. I will say that the #1 problem I see on swaps is the fuel delivery system. You're not posting your calibration or a data log when it's running bad so no way anyone can really help.

[Crzna442]

Thank you for your response. I apologize if my terminology kept people from trying to help me - "log in and log out" made sense to me I guess but now that you mention it I can see how that might be misleading. I guess the reason I didn't post my tune or data log is because I am almost 100% certain it is not a tune problem. At this stage I was more so looking for someone that could tell me they have run into a situation where when they disconnect the vehicle from the scanner the vehicle runs better. What happens in that disconnect process that could possibly make the vehicle run better? How does anything change at that moment? If someone could tell me that has happened to them and that it is still likely a tune issue then I would go down that path.

I've checked fuel pressure while idling and while driving in bad mode and good mode by using a pressure gauge on the fuel rail and it's a constant 56+ psi. Even if it was a fuel delivery issue why would it be fine immediately after disconnecting the vehicle from the scanner? I've tried so many different things spending hours upon days working on this. I feel like it's a computer problem - either my laptop or leaning more towards my ecm. Everything is the original GM setup with no changes from the donor vehicle so the tune shouldn't be this far out of whack. The only thing not original is I don't yet have an air box - I have a conical filter on the end of the original intake air piping - length hasn't changed...and regardless MAF and fuel trims are good.

I can post the tune and data log later today if you feel that would help. Perhaps it might make the issue I'm having more believable.

[dhoagland]

Do you have a different scanner you can connect and watch things like ECM voltage, and signals from your sensors? Lab Scope to watch signature voltages?
I know if one was acting up it SHOULD throw a code, but sometimes not.
Not exactly sure what connecting/disconnecting HP scanner would have to do with anything, but if we can identify an issue with other tools maybe this goes away.

Did you ever ride in the donor vehicle?

[Crzna442]

Thanks! Unfortunately I don't have a different scanner - I would have to take it to someone else for that - which I can do. Doesn't HP Tuners scan Control Module Voltage or is that different than what you mentioned as ECM Voltage? My Control Module Voltage in HP Tuners ranges from 12.5 to 13.5.

No I never rode in the donor vehicle - I heard it run but that's all. The motor only has 125,000 miles and it sounded good but that doesn't mean everything. Although it runs amazing when it's in this other mode.

I will get a log file posted here this evening as soon as I get it figured out how to do that - shouldn't be too hard - just gotta figure it out.

[Crzna442]

oh...I see they were already attached - easier than I thought. There is a log from one occasion when it was not working good and one occasion when it was working good.

[Crzna442]

DOD Disabled plus TCS changes.hpt

This is my current tune.

[dhoagland]

Can you log any kind of torque management?
I know on Diesels you can log what is derating fuel

[Crzna442]

If I can I'm not aware of how to - I'd have to research that. I know I can play with torque management settings but not sure if I can log it.

[dhoagland]

Try this (mine is a later e38 so you might not have these. There could be more named differently)
Connect you scanner
Click vehicle tab, then repoll (this refreshes your list if stuff has been added from a previous version)
Click add channels, click the gear
In text box type Torque

Here is what mine brought up. Ignore the blue highlights, those are what I'm currently monitoring.
You want stuff like ETC management Type, Spark Management type, Fuel management type, ETC...

Hope this might give some direction... But you seem to have a strange one for sure

[Crzna442]

I appreciate your response. I?ll try this on the weekend and report back. You?re right somehow I got a weird one.

[Crzna442]

I was able to add those torque management PID?s as suggested above but there were no differences between the bad mode and the good mode. My tuner is finished with the tuning now but he is also bewildered by this problem.

Today I changed the ECM and TCM thinking that would certainly fix the problem but it didn?t - same issue.

I guess I?ll just resign myself to the fact that I have to connect and disconnect my vehicle to and from the scanner whenever I drive it.

Truck drives amazing when it?s in the good mode - especially after the tuner made some changes. I just would like it to stay in that mode.

I just thought I would add this info here - there are so many of these strings on here that kind of tease you along but then they just end with no answer or even no follow up at all and I at least wanted to close this off. If I ever find the problem I?ll add to this string.