MGUNZ

My 98 K1500 5.0 finally died with just over 200K. I swapped in a 5.7 from a 99 Suburban 1500, took complete engine and ECU from the burb but truck would not start? Swapped out ECU with my 5.0 and truck started right up, however runs like crap, service engine light on(flashing) code reads cylinder 6 misfire...what's so confusing is that the engine ran great in the suburban as it was a replacement engine with 15K on it. ANY help will be greatly appreciated...I'm being told its a fuel pump, fuel filter, swap out entire wire harness, "flash" ECU?? I am willing to pay for help, just not willing to pay for the guessing game....thanks in advance.

Ronin1014

Your ECU is confused because it's programmed for the 5.0. The problem with the 5.7 ECU is the truck is in tamper mode. The ignition does not recognize the ECU and the ECU does not recognize the ignition, both are telling the truck it has been stolen and not to start. If you have the suburban still there is a chip under the dash you need, you are looking for a grey box in the wires on the drivers side near E-Brake control pedal. Try popping that chip in the truck and the 5.7 ECU.

If that does not work, do some research on resetting the ignition passlock, either way you will want that ECU from the 5.7.

*EDIT*
I just had this problem a month or so ago, only difference was I was going 99 5.7 to 98 5.7 so my original ECU was fine and incidentally the better choice.

MGUNZ

I will try that this morning and thanks for the tip...I figured it was something like that just no clue where to start...Ill keep you posted to the results.

Ronin1014

Yeah, back around that time Ford was having issues with high theft rates, Car thieves would spend a couple hundred on an ignition lock cylinder and simply swap the ignition lock. At that time it was literally as easy as the push of a button and in forty five seconds or less they had a key to the truck. GM saw this and answered with the passlock system along with a retardedly difficult to remove ignition system. Now ten fifteen or more years later it's sort of in the way for those of us who want to keep our 200000+ mile companions alive.

I am definitely interested in your results as I intend to upgrade my engine from a 5.7 to a 7.4 when finances allow or inexpensive opportunity strikes.

My knowledge of the chip under the dash actually comes as a bit of an accident and is paired with a little bit of assumption. When I swapped my motor out I bought a truck that was destined for the scrap pile. While stripping the vehicle I stumbled across the chip and asked a knowledgeable friend and he said it's a "stupid thing with the ignition system, the truck won't run without it" Figuring my truck had it all ready I tossed the chip into a box of misc circuitry and forgot about it. A week later I had the motor and CPU from that truck into my truck and was having the same issues you experienced. After not being able to find the chip I put my CPU back into the truck, that said I have not tested the chip change with the CPU. If it does not work I want to know and we can research the passlock reset because the Service and tech reps at the dealership would not help me out on that.

MGUNZ

Well, I found the grey box and the chip in the 99 Suburban...thought this couldn't be this easy can it??...went to my 98 to do the old swap and low and behold....NO such creature in the 98.....so now both vehicles are headed back to the repair shop to have the entire wire harness swapped out...at this point its not about the money but rather getting this truck running smoothly again!! I will keep you posted.

Ronin1014

There has to be one in the 98. My 98 had one, that was how I found out about the little grey box, it was there when I tore it down to send to scrap. Give the 98 another more in depth look through.

MGUNZ

ok, good news I found the grey box with chip on my 98...I did the swap but still not running 100 percent. My neighbor is a good mechanic, just never any time but he came down and plugged his laptop into my truck, then he told me to plug in the 5.7 ECU....bingo the truck was now reading as a 99 Suburban, he found the VATS (Vehicle Anti Theft System) program and disabled it and the truck now is running with the correct ECU. I put new plugs, wires, cap, rotor but I still have a flashing Service Engine light and truck not running 100 percent...still feels like cylinder 6 not firing??

Ronin1014

Now I would say double check your plug wires, I actually had the same issue, my #7 was misfiring, it was literally a simple mix up of the wires at the distributor.

MGUNZ

OK, today I will go back and recheck all the wires, pull number six and use a spark test...is it possible to be 180 out with the distributor like the old school chevys?

Ronin1014

I actually got away with not pulling my distributor out, I suppose it could but it would be very unlikely with the position of the coilpack and its short wire.

But never the less, on the distributor cap with the motor being front and the firewall being back 1,7,3 and 5 are on the drivers side in that order front to back. 8,2,4,6 and coil are on the passenger side in that order front to back.

On the motor it self with the fan being front and the firewall being back, 1,3,5 and 7 will be on the drivers side in that order from front to back. 2,4,6 and 8 are on the passenger side in that order front to back.

If you really want, you can check your timing the old school way, line up the marks on the harmonic balancer and check it to the distributor where it should be pointed at a little arrow on the distributor. but I am more inclined that this will be a wire or plug issue, since they are all new it's most likely a wire.