Engine/Transmission (1998.5 - 2002) Which one is failing? VP44, Map Sensor, or Edge Comp?

[Sticks]

This one stumped me. See my signature for upgrades.



Went to run some errands yesterday, and on startup, the truck stumbled and died immediately after the usual 3 engine rotations on initial crank.



Started the truck up again, a little puff of white smoke and all was good.



After the engine got to operating temps, I did a rev test (from idle to WOT - mashed the throttle). I got a second or so of stumbling, a bit of white smoke, then an arse load of black. Did it a couple more times with the same result. Now here is the kicker. I turned the comp box on (set at 1 X 1) and did another rev test. Ran fine, expected amount of black smoke (significantly less than with the box off) at first then cleared up and smooth.



I checked for codes and all I have is the usual 1693 and a 0236 (map voltage too high, too long).



I no longer have access to a scanner to observe the sensor downstream readings, so I don't know if my MAP is constantly showing high pressure, or even reading at all. Boost, fuel pressure and EGT's are all normal.



Otherwise the truck runs fine. I usually run with the comp box and water meth inject. off. I only turn them on when I want to play or EGT's are an issue (towing, hill climbing ~ EGT's 150* cooler with the Comp on driving in the mountains).



So, until I figure this one out, the Comp box stays on full time.



Opinions?

 

[Sticks]

Seriously? Nobody?

 

[DavidC]

Could be the map sensor code. I was getting a map sensor low with a scanner and it did not set the check engine light. I had a new map and installed it. Same code, kept resetting and it always came back. I started fiddling with the wires at the convoluted tubing with the map wires and the code went away. Apparently from vibration and the harness dangling out there the wires were chafed. I would check all the map connections visually and with ohmmeter wher you can and try to make sure you do not have a short to the ECM wire reading the return signal. I had the laptop connected when I was trouble shooting mine at the time. If it is a intermittent short that will be a lot harder to find. Have you tried a new Map?



Dave

 

[Sticks]

Not yet. Time is a commodity that I don't have. The truck right now is just an errand runner for another 3 weeks until I need it for a trip. Emissions need to get done for registration though.

 

[PC12Driver]

The stumbling right after start does not sound like a MAP sensor to me. A bad MAP sensor usually shows up as low power or a bunch of black smoke, since its job is to balance fuel to available air. Stumbling at idle from a bad MAP would surprise me.



You can get a MAP overvoltage if your Comp's ground is loose (path of least resistance ends up through the MAP if the ground isn't there). I've also had the truck do some funny things when my +12v lead to the Comp became loose. With that in mind, I'd start by checking the power and ground connections to the Comp (at the source and the plug on the back of the Comp box as well), and then move on to totally disconnecting the Comp and see what happens. You can pull the plug out of the back of the Comp box to remove it from the system, but you'll still need to remove the "Y" at the MAP sensor and plug the truck's harness in directly to the sensor. And then of course limit your right foot to 20psi of boost to prevent defueling and a code.



I'm thinking it's bad hot or ground to the Comp, or the Comp itself.

 

[Sticks]

I will double check the power and grounds. I may relocate the comp ground from it's current location (same as the grid heater ground) as there may be some back feeding.

 

[Sticks]

OK, so I removed the Comp from the system and the ol' girl runs normal. Nice and smooth, expected smoke withe the 100 hp injectors.

Just for the entertainment value I laid into it. Turbos spool hard at 15psi... wham... defuel... . turbo inertia still ran up to 27psi then dropped.

This weekend I rewire the power & ground for the comp and try again. Still need to install the mechanical boost fooler (pressure regulator - occasionally get over boost codes with the comp hooked up, even before with my Edge EZ). Been a while since I have been back in there. Forgot where that MAP was located and what a pain it is to deal with that safety lock on the connector. Hopefully I have the NPT adapters in my work truck to neck down the port for the regulator.

Mystery question... The Edge Comp is for an 01 (picked it up from a customer at work who fried his VP and turbo... no gauges). How is Edge about checking out the functionality of their units and cost of refurb/repair?