LM7 5.3L DBC to DBW swap - doesn't start
12-01-2016, 03:08 PM
#1
On The Tree
Thread Starter
LM7 5.3L DBC to DBW swap - doesn't start Since my HPT thread isn't getting any hits:
I have a 1989 240SX with an 99 Silverado LM7 in it in front of a NV3500 manual trans. I've been running an OEM LM7 ECU for over a year with just VATS turned off. I found an uncut 04 Suburban L59 DBW Flex Fuel harness with the bigger injectors so I decided to swap over.
I'm using the truck fuse block on both harnesses. Fuel pump is controlled through a switched relay external from the harness.
The car runs perfectly fine on the LM7 harness but once I swapped to the L59 Harness (including pedal/TAC/DBW TB), it's not starting. I'm reading all the main sensors on VM Scanner and the gas pedal is actuating (I press on the pedal before I start cranking in the log), just not sure what I'm missing. I don't have the O2 sensors hooked up because I was too lazy to get under the car for that just for the test fire. I don't think that would affect anything though.
I'm relatively new to HPTuners. I disabled VATS and some of the Emissions CELs then flashed the ECU, that's the only thing I've done to it.
I've included the scan file - please let me know if something looks off (or if I need to log additional parameters). Thanks in advance!
Everyone was asleep last night when I got it finished so I couldn't check spark/fuel. Will do tonight.
L59HarnessEDUnostart.hpl
L59FlexFuelECUstock.hpt
I have a 1989 240SX with an 99 Silverado LM7 in it in front of a NV3500 manual trans. I've been running an OEM LM7 ECU for over a year with just VATS turned off. I found an uncut 04 Suburban L59 DBW Flex Fuel harness with the bigger injectors so I decided to swap over.
I'm using the truck fuse block on both harnesses. Fuel pump is controlled through a switched relay external from the harness.
The car runs perfectly fine on the LM7 harness but once I swapped to the L59 Harness (including pedal/TAC/DBW TB), it's not starting. I'm reading all the main sensors on VM Scanner and the gas pedal is actuating (I press on the pedal before I start cranking in the log), just not sure what I'm missing. I don't have the O2 sensors hooked up because I was too lazy to get under the car for that just for the test fire. I don't think that would affect anything though.
I'm relatively new to HPTuners. I disabled VATS and some of the Emissions CELs then flashed the ECU, that's the only thing I've done to it.
I've included the scan file - please let me know if something looks off (or if I need to log additional parameters). Thanks in advance!
Everyone was asleep last night when I got it finished so I couldn't check spark/fuel. Will do tonight.
L59HarnessEDUnostart.hpl
L59FlexFuelECUstock.hpt
12-01-2016, 07:52 PM
#2
Did you do a write entire on the PCM when you disabled VATS? If not, you need to. If I remember correctly VATS can't be disabled without a write entire.
I would also set P1626 and P1631 to "No error reported."
Your log is really sparse. Try logging "VATS Status" in the HP Tuners scanner and see what it says. I would also log the fuel injectors and see if they are trying to pulse. Since you have spark for a short bit, I'm assuming that is when you are cranking the engine.
Does the engine even attempt to fire or does it just crank?
I would also set P1626 and P1631 to "No error reported."
Your log is really sparse. Try logging "VATS Status" in the HP Tuners scanner and see what it says. I would also log the fuel injectors and see if they are trying to pulse. Since you have spark for a short bit, I'm assuming that is when you are cranking the engine.
Does the engine even attempt to fire or does it just crank?
12-01-2016, 11:12 PM
#4
On The Tree
Thread Starter
After playing with it tonight I found good fuel pressure, injectors are opening. Pressure was holding at the rail, cranked it over and the pressure went down when cranking, exhaust smells like fuel.
Had the fiancee crank it over with a spare spark plug in one of the coil wires and it's not sparking. The coils are getting 12V to the pink wire on each coil.
The throttle pedal says "20%" when it's actually at 0, does that matter? It goes up to 100% when I open the pedal up fully.
12-02-2016, 08:54 AM
#6
On The Tree
Thread Starter
Did you do a write entire on the PCM when you disabled VATS? If not, you need to. If I remember correctly VATS can't be disabled without a write entire.
I would also set P1626 and P1631 to "No error reported."
Your log is really sparse. Try logging "VATS Status" in the HP Tuners scanner and see what it says. I would also log the fuel injectors and see if they are trying to pulse. Since you have spark for a short bit, I'm assuming that is when you are cranking the engine.
Does the engine even attempt to fire or does it just crank?
I would also set P1626 and P1631 to "No error reported."
Your log is really sparse. Try logging "VATS Status" in the HP Tuners scanner and see what it says. I would also log the fuel injectors and see if they are trying to pulse. Since you have spark for a short bit, I'm assuming that is when you are cranking the engine.
Does the engine even attempt to fire or does it just crank?
On the old LM7 ECU (before I disabled VATS), it would fire/run for a second or two and then die. The L59 ECU doesn't fire at all.
Thanks for the help, I'd rather not have to swap back to the DBC harness.
The Throttle Body is the only thing not from that engine - it's from my L33 (2006 VIN B Silverado 1500) but everything else is from a 2004 L59 Suburban. The part number is the same on RockAuto FWIW
Last edited by FlatBlack; 12-02-2016 at 09:58 AM.
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12-02-2016, 09:45 AM
#9
On The Tree
Thread Starter
It's attached to a coil bracket bolt. ****. I thought that it would make contact with the head at some point but it's possible it's isolated by the gaskets.
09-20-2020, 10:12 AM
#13
Are the plugs actually firing? Are the injectors getting a signal to open? A lot of the early swaps with the OE computer had to have the VATS disabled. I ran into this in 2012.
09-20-2020, 11:41 AM
#14
TECH Senior Member
The following 2 users liked this post by G Atsma:
Old Geezer (09-21-2020), SwapStang (09-24-2020)
