LT1 swap runs for few seconds, dies
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Joined: Mar 2016
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LT1 swap runs for few seconds, dies Hey, new user here and this is my first time working on this generation of vehicle. This is a real stab in the dark, but I'm out of ideas short of throwing parts at it.
My elderly neighbor has a 49 Chevy pickup with a 96 LT1/4L60E swap. The swap was done by a shop around 10 years ago and was done very, very poorly. Sadly, his memory and health are failing and he wants to get the truck sold and move to a smaller place. It's been parked for about two years, ran and drove fine prior. The aim is just to get the engine running so they can get a decent price for it. I'm not prepared to fix all the sins from the shop that did the swap.
The engine runs for 5 to 15 seconds then dies. It'll rev while running and sounds great, and it's an orderly shutdown. The PCM is throwing P1641 and P1642 only. I haven't been able to pull anything else of use from the PCM. Live PID monitoring shows nothing unusual (airflow rates, TPS, etc, all follow correctly). The PCM does not report any vehicle information.
The stamp on the engine block and tranny is 4TR422503. The first digit might be a 1? The PCM has the following stickers:
16214399 BSCZ
16229991 BSCZ
86BSCZ263263Z3G
The swap........ Oh boy.
It has a GM tilt column - metric, 79 and later. Butchered with an external horn button on the column. Fuel tank from the donor just strapped into the bed. Wiring is an absolute nightmare. Loose wires, random junctions, wires just stuck into connectors then duct taped together, fuses everywhere, multiple fuse boxes. There is a single fan on the radiator with a relay, but I haven't traced how that is controlled. The vent for the opti is NOT connected - all the parts seem to be there, they just pulled the suction hose and capped it. There are multiple loose connectors in the engine bay with nothing apparent for them to connect to.
As an example, if you just try to start the engine, the starter clicks and all power is lost, almost as if a circuit breaker trips. Power is even lost to the aftermarket gauges. Turn off, wait a moment, it'll reset but do the same thing. Trigger the starter with a remote start switch, and you can then stop and start the engine just fine. I don't know where that's coming from, and worried it would take hours to pull apart and reassemble the rats nest of wiring.
Possible causes I've already chased down:
1) Bad fuel - flushed the lines, drained tank, fresh gas
2) Fuel pressure - replaced pressure regulator (it was leaking badly), holds 40 to 45 PSI (with vacuum disconnected) the entire time its running
3) VATS - there is no BCC/VATS box that I've found. I can only assume VATS was disabled in the PCM. I have not attempted to trace the fuel enable wire, and, frankly, I'd rather not.
4) Oil pressure - aftermarket oil pressure gauge shows good pressure
5) Maintenance - cleaned the intake tube and MAF. The engine is also covered in mice crap. No apparent signs of chewed wires though. Using a good (nearly new) battery and keeping a charger connected.
On the OBDII side, I have an OBDLinkMX and OBDKey130 bluetooth dongles. The only software I have is OBDWiz (basic tool from Scantool) and the OBDKey stuff (similar capabilities).
Any ideas where I should look next?
Is the 1641/1642 enough for the PCM to shut down the engine?
How can I confirm it's not the VATS? I think I saw somewhere that a VATS failure throws a P46? Seems odd for something like that to fail only after being parked.
Thanks!
My elderly neighbor has a 49 Chevy pickup with a 96 LT1/4L60E swap. The swap was done by a shop around 10 years ago and was done very, very poorly. Sadly, his memory and health are failing and he wants to get the truck sold and move to a smaller place. It's been parked for about two years, ran and drove fine prior. The aim is just to get the engine running so they can get a decent price for it. I'm not prepared to fix all the sins from the shop that did the swap.
The engine runs for 5 to 15 seconds then dies. It'll rev while running and sounds great, and it's an orderly shutdown. The PCM is throwing P1641 and P1642 only. I haven't been able to pull anything else of use from the PCM. Live PID monitoring shows nothing unusual (airflow rates, TPS, etc, all follow correctly). The PCM does not report any vehicle information.
The stamp on the engine block and tranny is 4TR422503. The first digit might be a 1? The PCM has the following stickers:
16214399 BSCZ
16229991 BSCZ
86BSCZ263263Z3G
The swap........ Oh boy.
It has a GM tilt column - metric, 79 and later. Butchered with an external horn button on the column. Fuel tank from the donor just strapped into the bed. Wiring is an absolute nightmare. Loose wires, random junctions, wires just stuck into connectors then duct taped together, fuses everywhere, multiple fuse boxes. There is a single fan on the radiator with a relay, but I haven't traced how that is controlled. The vent for the opti is NOT connected - all the parts seem to be there, they just pulled the suction hose and capped it. There are multiple loose connectors in the engine bay with nothing apparent for them to connect to.
As an example, if you just try to start the engine, the starter clicks and all power is lost, almost as if a circuit breaker trips. Power is even lost to the aftermarket gauges. Turn off, wait a moment, it'll reset but do the same thing. Trigger the starter with a remote start switch, and you can then stop and start the engine just fine. I don't know where that's coming from, and worried it would take hours to pull apart and reassemble the rats nest of wiring.
Possible causes I've already chased down:
1) Bad fuel - flushed the lines, drained tank, fresh gas
2) Fuel pressure - replaced pressure regulator (it was leaking badly), holds 40 to 45 PSI (with vacuum disconnected) the entire time its running
3) VATS - there is no BCC/VATS box that I've found. I can only assume VATS was disabled in the PCM. I have not attempted to trace the fuel enable wire, and, frankly, I'd rather not.
4) Oil pressure - aftermarket oil pressure gauge shows good pressure
5) Maintenance - cleaned the intake tube and MAF. The engine is also covered in mice crap. No apparent signs of chewed wires though. Using a good (nearly new) battery and keeping a charger connected.
On the OBDII side, I have an OBDLinkMX and OBDKey130 bluetooth dongles. The only software I have is OBDWiz (basic tool from Scantool) and the OBDKey stuff (similar capabilities).
Any ideas where I should look next?
Is the 1641/1642 enough for the PCM to shut down the engine?
How can I confirm it's not the VATS? I think I saw somewhere that a VATS failure throws a P46? Seems odd for something like that to fail only after being parked.
Thanks!
Thread Starter
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Joined: Mar 2016
Posts: 3
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Vacuum seemed fine. At least, the PSI reported by the MAP sensor certainly reacted. IIRC, it would get down to 2 to 3 PSI in the short time it was running.
Don't know if an injector is stuck open, but it didn't seem like a rich stumble. Any way to tell other than pulling the fuel rail and inspecting the injectors?
Don't know if an injector is stuck open, but it didn't seem like a rich stumble. Any way to tell other than pulling the fuel rail and inspecting the injectors?
Look more into the VATS. I helped my buddy put a cage in his car. IT would start and runs fine for about 5-6 seconds then die. everything looked good. After a couple hours we found the Vats modual we had left out. Plugged it in and all was well. His PCM was suppose to had vats tuned out as well.
Thread Starter
Registered User
Joined: Mar 2016
Posts: 3
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Does a VATS problem throw a P46?
And how can I do a tune modification on a 96 PCM for free/cheap?! From what I can tell the 94/95 PCMs have free tools available, but the 96/97 units require a $400+ software package, or acquiring a tune from a vendor ($150+?).......
And how can I do a tune modification on a 96 PCM for free/cheap?! From what I can tell the 94/95 PCMs have free tools available, but the 96/97 units require a $400+ software package, or acquiring a tune from a vendor ($150+?).......