Car Won't stay running after engine swap
 

Hey guys. I have had an interesting journey with this. If you want the history...see here: http://www.aleromod.com/forums/showthread.php?t=35829

In summary, my daughter blew her head gasket (2003 3.4 alero). The heads were warped too bad so I opted to pull a 1999 engine from a junk yard and throw it in there using several of the 2003 components. That engine had a slightly blown head gasket as well. I changed that out, had the heads surface ground etc. and I got two of the push rods swapped and bent a valve. Pulled it all apart again, had the valve work done, new gaskets, and now finally it runs smooth, no overheating...everything is back to normal....ALMOST.

I let the car idle in the driveway for about 20 min to let it get to temp etc before driving it. I then drove it through the neighborhood and everything seems fine. Only problem I'm having is the car won't idle. If I completely remove my foot from the gas it may sputtter a little, and then die. I have verified that the IAC is moving in and out when the ignition is started. I made sure the throttle body is nice and clean and there is no buildup in the IAC. Some people have suggested that since the car sat for so long without a battery (and that I changed several components), that the car needs to be driven more so that the computer can re-learn all the parameters. Does this sound feasible or does it sound like something else? Any help would be greatly appreciated as I am SICK of this project. Thanks!

couldnt it be fuel related, like fuel pump going bad

have you tested fuel pressure? try a new fuel pressure regulator. unplug the MAF sensor to see if it will idle, but be prepared the tranny will shift very very hard from neutral to drive and to reverse.

The computer will not cause a stall condition. Check the fuel pressure readings at idle and also check for vacuum leaks. How old is the gas in the fuel tank? Try some fresh fuel to see if that helps.

mine does, it hunts at idle sometimes because im still working on my fuel trims, so yes a PCM will cause stall conditions, but it is less likely in this scenario, but a MAF sensor going bad can cause the same issue.

Thanks for the replies guys. If it was a MAF sensor wouldn't I be getting some sort of code like a P0101-P0103? Or a Lean/rich or fuel trim type code indicating a fuel problem?

And the reason I inquired about the computer was because on my Dodge Ram, it did the exact same thing until I drove it for about 40 miles. I researched on the net, and it's a pretty common problem when battery has been disconnected for quite some time...but didn't know if any of you guys had experienced somethign similar with these cars.

Fuel pump was replaced about 6 months ago. And once again, it's not showing any signs or rough idle or anything other than it just won't stay running if you take your foot off the gas. And didn't have any issue prior to doing the engine swap. I probably should have also mentioned that when I drove it, I can give it gas and it revs and accelerates fine, no bogging or other issues, aside from idle.

Does your pcm still think your running the old motor? 99 motors had some slight diffrences

Good point. I haven't done anything to the PCM, which is why I thought my question regarding "re-learning" was valid. I used most of the components from the 2003 motor (fuel rail, injectors, cps, all the sensors etc....so I think I should be good?

check the fuel pressure.

Fuel pressure should be fine... What about the throttle body is it closing at idle to far and choking itself out???

I didn't think 99's had EGR? but that wouldn't cause the issue your having.

I agree with Eric and wonder if the TB is closing too much. Never heard of it on a FI car, but it could be possible. What about the fuel filter? A faulty fuel pump on these cars is never in the "going" stage. It has two different operating moods. Working or Not working.

Check to see if the coil packs are tight. Plug wires aren't loose on the plugs. No burn connections bewteen the ICM and wireing hardness

if you drove it for 10 miles thne you probably let the computer relearn what ever it needs to to make adjustments. have you driven it since? as far as any of the sensor going bad and not throwing a light: if the sensors still within "spec" but is no where near the useable area (such as maf sensor thinking there is a shit-ton of air going in when realy your idleing) thne it can cause weird things and no lights.

i will say that when i had to replace my fuel pump a couple months ago, i went to a friends and the store and back to my dorm and everything was fine...i went out 5 minutes later to go check on something and it had a slight stall at idle, drove it about 3 miles in the country and as soon as i let it drop to idle it was gone...the code came on about 30 seconds before it got to the point of refusal to start.

Car most likely needs a crank relearn, performed with a Tech 2 at your local friendly money-loving dealership.

I've done 10-15 GM engine swaps with no mishap, about 5 were 3400s, but I did have one that ran fine for 5 minutes, then bogging down. Only fixed was a crank relearn. (First the dealership sold me a MAF, but I made them take it back when it didn't fix the problem -I was selling the car anyways)

unplug o2 sensor(s) (upstreams)

see if problem goes away

It sort of seems like this could be what's happening, but how do I check that?

I have driven it, but probably only about a mile or so through the neighborhood. Maybe just to mark that out of the equation, I should take it for a "spin"

I will give this a go and report back. Thanks.

Thanks, I will exhaust all the other suggestions made here first before going the "dealership" route, ouch!

Speaking of MAF sensor....When I was pulling the air intake "box lid" off I lifted too much and broke one of the tabs that holds it down. Could it be "sucking" air without going through the filter first and causing additional problems, or is that a stretch (I'm sure you can tell I'm grasping at straws at this point).