411 PCM swap nightmare

[Kirmetoads94]

Hey fellas, I bring you here today because I am at my wits end with this swap and am about to go back to my black box and pout until the end of time.

I have a 1997 Suburban that I keep very well maintained and super clean. It ran very well before this PCM swap, I chose to do it because of the tuning capabilities and most important (to me) the Tow/haul mode and E-fan control.

I started by ordering a 411 off of eBay from a "reputable seller" that promised to have every specification from the buyer put into the computer.. well I'll tell you that wasn't the case. A few weeks went by and my own tuning software came in and I jumped on it and my tune was a mess. I grabbed a stock 2002 Express van bin from the repository and flashed it to the PCM to start from scratch.

As soon as I got to a point where I could finally turn the key the thing ran like S**T, ok no problem the EGR isn't hooked up yet (97 EGR is controlled differently ~add wire) so I got that done and it seemed to run better. but that was short lived...

I took it out for a test drive and about 5 minutes into driving I realized that I had serious problems. The SES light started flashing and the truck kept going in and out of lock up and I just watched as my transmission temp sky rocketed. I limped it home and read the codes P0300 and another one for cylinder 4 misfire (How? it was fine before the swap???) The suburban started idling very badly, it felt like it couldn't stop surging.. So I figured it probably needed a CASE relearn so I grabbed my Tech II and did it.

Here's the cool part, now I dont read any misfires at all but I can literally still feel it surge at idle and overall just has a rough idle to the point that I feel uncomfortable driving it. It doesnt go in and out of lock up anymore on the hwy but right around 30-35mph it'll do it for a split second and I cant seem to get my scanner to see why....

I have checked all the wires to make sure they're in the right place countless times and I'm 110% certain its all right. The spreadsheet I got from Lextech says that the EGR and EVAP are controlled differently than in 98 and 99 and the 411 PCM doesn't support them. Can the evap cause my rough idle issue? I have so many questions and I cant seem to find ANY answers for them.... So please..... Help!!

Things Ive checked /replaced:
Fuel pump pressure 58PSI
MPFI upgrade
New Plugs, wires, cap, rotor, and fuel filter
Cleaned EGR
Timing is dead on at 0*

 

[Phillip Buessing]

Ok, here is what i would do in your situation, but keep in mind I am not an expert in these pcm swaps. I have done one, and I did not use Lextechs spread sheet. I would make sure the bin file is for your correct transmission, you did not specify whether your burb has a 4l60e or 4l80e. Maybe try a bin from another source just to rule out the possiblity of a corrupt file. I don't know what Lextechs spread sheets are like or if there are different ones for the 96-97 and 98-00 trucks but if there are make sure you have the correct one.

You mentioned you have a Tech II, hook it up and go through all your engine/trans data with it running and not running, make sure everything looks "normal". By your description it sounds like the engine is missing on one or more cylinders(P0300 and presumably P0304). If this is the case you need to narrow down which cylinders are the issue. Do a cylinder power balance test with the tech 2. Do a fuel injector balance test also. By the way, if you do a CKP sensor relearn with the engine missing, it "learns" the misfire(normally it won't allow the procedure, but I have seen this happen) this could be why you are no longer getting misfire counts.


The emissions devices(EGR, EVAP purge, EVAP vacuum switch) could all be unplugged an it should still run fine but will set codes. You can also unplug the MAF and start it, it should just default to speed density and run normal but set codes.

If you think it is not a misfire but an overall fueling or spark issue, something in your data should be awry leading you to the cause. You mentioned u replaced ignition parts, and mpfi conversion. Were these done at the same time as the pcm swap? or before or after? DOUBLE CHECK EVERYTHING. I have had problems with some aftermarket distributor caps being faulty out of the box causing all kinds of weird misfire problems--stick with OE caps and rotors.

Good luck