1999 Tahoe Stalling Issue

[Dan Barlow]

He's running it off off 0411 computer which I think goes to a 5.3 LS motor with a automatic. That's about all I'm good for . Well other than say run it off a aftermarket engine management system .

[Eric]

Fuel pressure is fine, and I can rev it all day long. Its when I have it in gear with the brake on I can torque it up to about 2k RPM, it holds no problem, but the second I let off the gas it kills the ignition flat dead. Its not the 5.7 with the spider, we put in a big block 454/4L80 combo out of a motor home, all the connectors were the same and it was a relatively easy swap. Was running great for a while but then he started having some strange transmission issues that we couldnt figure out but it kept going. He got in one day and it wouldnt stay running, found a ground wire and it would run but then it started this current issue. Im open to the idea of maybe theres a safety feature where it kills the ignition when it tries engaging OD in 1st gear, but I need proof lol

The truck stock, controlled the ign through the ecu.
You don't say if this 454 is a tbi and computer controlled distributor ign , or a csrb and mechanical timing with vac advanced can distributor.
THe 350 ecu is not going to fuel and ing advanced maps correctly for a tbi 454.
and the 350's fuel system, the fuel pump is to high of pressure if it is using a carb.
Those trucks go into a limp home mode also. if (iirc) the pink wire going into the transmission looses power from the ign switch.

[Eds_Automotive]

what's the fuel pressure? a failing pump on that spider-efi could cause that.
outside of that, have you checked all the connections and grounds? if it ran fine before (how long? miles?)
what is the starting procedure now? do you have to hold the throttle down to start?

Fuel pressure is fine, and I can rev it all day long. Its when I have it in gear with the brake on I can torque it up to about 2k RPM, it holds no problem, but the second I let off the gas it kills the ignition flat dead. Its not the 5.7 with the spider, we put in a big block 454/4L80 combo out of a motor home, all the connectors were the same and it was a relatively easy swap. Was running great for a while but then he started having some strange transmission issues that we couldnt figure out but it kept going. He got in one day and it wouldnt stay running, found a ground wire and it would run but then it started this current issue. Im open to the idea of maybe theres a safety feature where it kills the ignition when it tries engaging OD in 1st gear, but I need proof lol

[SuperBuickGuy]

what's the fuel pressure? a failing pump on that spider-efi could cause that.
outside of that, have you checked all the connections and grounds? if it ran fine before (how long? miles?)
what is the starting procedure now? do you have to hold the throttle down to start?

[anotheridiot]

90 suburban. In gear at long lights, dies. Other than that.. Fine. Changed lots stuff. Said to be torque converter...

That was why I was thinking solenoid, especially when he said there was trouble engaging overdrive. If it does not engage when its supposed to, it could be trying when its not supposed to. Letting off the gas is that little lull you get when you are in overdrive and it makes it feel like you let up the gas, have that little lag when you go to accelerate again.

The only thing that made my 98 Malibu just die for no apparent reason was tied to the pass key system. Sometimes it would not start, no crank, nothing but security lite on, wait 5 minutes, it would start. If you drove for more than 20 minutes, you could be driving and it would just die for no apparent reason, if you were driving, bump it to neutral, turn key to start again and just keep driving. Troublesome spot was if you were in a turn and lost power steering at that time because it died. If you eliminated everything else, I guess I would go there..

[Deaf Bob]

90 suburban. In gear at long lights, dies. Other than that.. Fine. Changed lots stuff. Said to be torque converter...

[Eds_Automotive]

I just have a 99 Jimmy. wont hold in 4wd high, if I leave the car off for 3 days it does not start.If its in 4wd low, it stays there it revs up to about 5 miles per hour and slams into second. It slams into second if I take it on the expressway and we go from wide open traffic to bumper to bumper back in chicago.
They seem to have an ignition issue to me, like there is enough battery to engage and have the starter rotate, no problem with the fuel pump side since the non start ends up with a flooding issue, but does not have enough for ignition to light the mixture.
So when you say trans issues, I see electrical, dying for no reason, voltage drop that kills ignition. So it adds up to me that something is drawing power on the trans that is taking away the necessary voltage to keep the car running. Its like overall voltage drops below 11.5 the ignition just fails miserably. Add a computer into it and hence the gremlins.
So I get its a Tahoe and all, different motor, but the mindset of 1999 seems like the ignition is not on the proper level of importance.
You go 1996-1998, the best alternator trouble light is the ABS light.

Voltage drop is not the issue, its getting 14.2v even when its in gear and under load. Going to run through grounds again, it seemed to happen less or almost not at all after the customer reattached a ground behind the head.

[anotheridiot]

I just have a 99 Jimmy. wont hold in 4wd high, if I leave the car off for 3 days it does not start.If its in 4wd low, it stays there it revs up to about 5 miles per hour and slams into second. It slams into second if I take it on the expressway and we go from wide open traffic to bumper to bumper back in chicago.
They seem to have an ignition issue to me, like there is enough battery to engage and have the starter rotate, no problem with the fuel pump side since the non start ends up with a flooding issue, but does not have enough for ignition to light the mixture.
So when you say trans issues, I see electrical, dying for no reason, voltage drop that kills ignition. So it adds up to me that something is drawing power on the trans that is taking away the necessary voltage to keep the car running. Its like overall voltage drops below 11.5 the ignition just fails miserably. Add a computer into it and hence the gremlins.
So I get its a Tahoe and all, different motor, but the mindset of 1999 seems like the ignition is not on the proper level of importance.
You go 1996-1998, the best alternator trouble light is the ABS light.

[Eds_Automotive]

Still looking for ideas. I have never had this happen before, any help is appreciated.

[Eds_Automotive]

clearly has transmission issues so thought would be a torque converter lockup solenoid. had a 4l80e that had strainers in the valve body packed with aluminum duist and shavings that did not allow fluid to go where it was needed. I am pretty sure the converter locking up in any gear other than fourth will just kill the motor. Mainly sounds like gremlins that make you change everything.

It doesn't seem like its doing that, I imagine it would be more of a sputter kind of stall. Plus, when its in drive or reverse, it moves just fine until you let off the gas and then it cuts off like someone turned the key. He was having trouble with the TC not engaging overdrive, which sounds like the exact opposite of what you described. Yeah, gremlins makes more sense at this point after all the work thats gone into it lol.

[anotheridiot]

clearly has transmission issues so thought would be a torque converter lockup solenoid. had a 4l80e that had strainers in the valve body packed with aluminum duist and shavings that did not allow fluid to go where it was needed. I am pretty sure the converter locking up in any gear other than fourth will just kill the motor. Mainly sounds like gremlins that make you change everything.

[Eds_Automotive]

Hello. I have an automotive shop in Florida. My customer brought in a 1999 Tahoe with a blown engine, and long story short we went ahead and dropped in a big block 454 out of a 1998 Fleetwood motorhome. Everything went well, it was running great for awhile. Has some transmission shifting issues but may be another issue. The problem we are having now is that it wants to stall in gear. It will start and idle just fine, revv the crap out of it and everything. Put it in gear and it will move no problem until the second you take your foot off the throttle then it dies as if the ignition was cut off. Flat dead, no sputtering or anything. It does have a 0411 PCM swap in it, we werent able to do a crank relearn because the transmission range switch has a code that wont go away, but its been running fine for a few months before this current problem came about. Any ideas on what it could be? The customer was able to get it to drive mostly fine when he reconnected a ground wire but its still stalling when you give it a load and let off the gas