I recently changed the 3.9 in my 90 Dakota with a 3.9 from a 91 Dakota. The car starts pretty good and idles great, it even pulls pretty good when your in the throttle (well for a V6 anyway). The issue is when you maintaining a consistent speed. It has a very bad surge. At highway speeds it almost acts like its dieing and restarting (its a manual trans), in town it feels like a bucking bronco, the whole car will jerk forward and backwards. This is a new with the motor swap thing, I believe. The old motor last ran last summer, and I swapped in the "new" motor before i drove it this year. The old motor was tired and was burning oil and antifreeze, and would not idle below 2500 rpm the last time I drove the car with the old motor.

We took the car on a 400 mile weekend (it was running much better at the beginning, towards the end it was getting worse). We did pull almost 20 mpg. The check engine light did come on a couple of times, but went off without shutting off the motor

When I swapped in the "new" motor, I changed the intake gaskets, installed a new thermostat, new plugs, the throttle body gasket, changed the valve cover gaskets, and replaced the O2 sensor.
I used the Throttle body off my old motor, and the year old plug wires & cap.

There is a cat converter, and the evap system is not connected, the solenoids are on the bench, there is no carbon canister. The egr valve is riding along.

I did the key on/off thing and am getting the following codes in the order they appeared.
12
36
52
32
31
21
41
55
Any input on what to start looking for? I have already recheck to make sure all the wires and grounds are properly connected, and I scrapped off the paint under the ground wires.
Help!
Gene

The codes should flash in sequence. I prefer to read codes with a scan tool. Did you try driving with the egr valve completely unplugged?

The egr valve is disconnected from everything except where it bolts onto the manifold.

I thought it was strange the codes flashed out of sequence too, but I went through the process 2 times and it did it the same both times. I don't have a code reader.

Back in the mid 80s I used to work on the Chrysler efi stuff, but its been so long I've forgotten most of what little I knew. The old standard was that if the computer did something wrong, it was defective, is that still the case?

I do have the computer from the truck the motor came out of, but it was an auto, and mine is a 5 speed, Will the auto computer work on my 5 speed truck?

The truck the motor came out of was wrecked. I did drive it around the yard before the starter crapped out, is it possible the dist is part of the issue? I used the one from the wrecked truck, I still have the original from my truck. Is it possible I have an intermittent loss of ignition?
What is code 36?
12 should be battery disconnected.
52 is O2 too rich or open
21 is O2 rich or open (only one O2)
32 should be evap, since there are no evap solenoids, these two make sense.
31 should also be evap
41 is gen field not switching properly
55 is end of test.

Is this correct?
I did have to change the plug on the new O2 sensor, I used butt connectors & changed wires one at a time in sequence, matching the wires to the same pins. Could that be the issue?
I haven't had time to mess with it today, but might have some time tomorrow. Gene

Is the motor you are using now, was it a magnum? They had lower distributor bushing and shaft wear issues. What is your base timing set at? How did you set it?

Motor is not a magnum.
The dist was marked before it was pulled, and was replace in the same location. I do not have a timing procedure for a 90/91 motor, I only have an 87 FSM.

Before the truck that the motor was in got wrecked, the previous owner supposedly put in a new timing chain. Motor only has 118,000 miles on it. Gene

code 36 is solenoid coil circuit (air switching)

code 32 is computer didn't see change in air-fuel ratio when egr activated - check valve, vacuum lines, and egr electrical

41 is alternator field control circuit open or shorted

Thanks, looks like I need to start at rechecking my wires and be sure one isn't broken or disconnected. The egr valve is not connected to anything, I suppose I could connect it, and the Evap solenoids and see if that makes the computer happy.

Can someone tell me the timing procedure for that 90 Dakota?
Any other thoughts?
Gene

For anyone interested, I have it fixed.

The problem was 2 fold.

1) One of the wire connections wasn't locking into place and was causing an intermittent, momentary break in the ignition. Once I got it to latch tight, most of the issue went away.

2) The timing was too far advanced.

The Evap system is still not attached, so on start up, I get a momentary check engine light that goes out after a few seconds.

I filled up the gas tank this evening and put about 15 miles on it, and all is well so far. We will give it a good test this weekend.
Thanks for the help. Gene