uwjberg

Been working on swapping this LM7 into my 1966 Skylark for a little over a year. I got it started up a month or so ago and it has been running well, although I've been taking it really easy to make sure I can work the kinks out. Finally got confident enough to drive into town (5 miles or so) and add some gas. On the way back I was feeling really good about how it was going and gave it full throttle for the first time. As soon as the pedal was all the way down it went into limp mode. I pulled over and didn't see anything immediately wrong. Turned the car off, and it restarted no problem. Drove home and put it in the garage. Torque Pro showed P1125 and P2125 for throttle/pedal position sensor issues.

I went back a few days later to try to troubleshoot and it cranks but won't start. It coughs a little like it wants to, but nothing happens. Now it shows different codes - P0220 and P2135, both for the throttle/pedal position sensors. With key on, the throttle body clicks and does a brief, small cycle where the blade opens slightly, but with the key still on the blade does not move when you press the gas pedal at all.

Here's what I have done:
-replaced the throttle position sensor
-checked the ignition/neutral safety switch relay (swapped a new one in, same result)
-pumped some of the fuel out to see if it was a bad batch. I don't see any water separating, so seems ok?
-I don't have a fuel pressure gauge but the pump primes and disconnecting the fuel line at the rail pumps into a container fine.
-Checked the plugs, connections at the pedal, TAC, PCM, throttle body
-Checked the crank sensor wires for damage since I have headers - they are fine (sensor is new)

I also called PSI since I have their swap harness and they said the motor should still start and idle even with the pedal/throttle codes so job #1 is just getting it started before I start trouble shooting the codes. He suggested ether into the throttle body to see if it fires. If so, it would be a fueling issue. This is my first LS and I'm not sure where to go next. When I crank it over I smell fuel so it feels like that's not the issue? I pulled a spark plug and it smelled like gas making me think ignition.

Would a faulty throttle body and these codes prevent start up? I'm just confused because everything worked great for 15 miles or so, which makes me think it's not a compatibility issue with pedal/TAC/PCM, etc. Any ideas on where to go from here? If the car should start even with these codes I'd hate to go through a trouble shooting tree if that won't even get the car started.

If it helps, here is what I have:
LM7 from a 2006 Silverado - cam and headers
4l60e from the same donor truck
Blue/Green PCM from the same truck - tuned by mailorder tuner to remove VATS, tune for the engine mods
PSI Conversion harness (HAR-1014)
the PSI C10 swap pedal ((ACC-1049) with pedal harness (HAR-1022)
New TAC purchased from PSI when I got the pedal
Corvette style filter/regulator - new with swap
255lph fuel pump - new with swap
New DW injectors

uwjberg

Update - I pulled a spark plug and held it against the head and I have spark. When I crank it over the tach registers some rpm so it doesn’t seem like it’s that crank sensor.

Also tested the relays on the PSI fuse block and those are good.

Old Buzzard

"-I don't have a fuel pressure gauge but the pump primes and disconnecting the fuel line at the rail pumps into a container fine".
It'll pump an open line at 2 psi. NOT a valid test.
First things first... A fuel psi gauge!

uwjberg

Well, I think you are on to something. No one local had a field pressure testing kit so I ordered one that will arrive tomorrow. But, I sprayed some starting fluid and the motor fired up and died after a couple seconds. Seems fuel related. That would point to either pump or filter/regulator right?

It seems hard to believe that either my brand new fuel pump or brand new filter/regulator went bad after 15 miles?
I'm also wondering if the limp mode and throttle/pedal position codes are related or totally coincidental?

uwjberg

Not sure if it's worth mentioning but after I try to start the engine I can hear fuel draining back into the tank. Some initial searching indicates that's probably not supposed to happen?

Old Buzzard

"Corvette style filter/regulator - new with swap
255lph fuel pump - new with swap".
How is this system plumbed?**
External pump?
How is the tank vented?
Bad/no vent could allow short run times, but after 10-15 minutes under load, the pump is working in a vacuum.
As of late, I've been seeing an increase in reports of faulty "Vette style" reg/filters. Only the WIX appears to have escaped some of the flak.
I don't use them.
"After I try to start the engine I can hear fuel draining back into the tank".
How is the return line plumbed?**
That pump should have a check valve in it, so it may be the regulator in the filter has taken a dump.
Thus, the no start and the noise.
As for the throttle faults... I don't think there's a connection. The engine should start & idle, as the PSI tech stated.

uwjberg

Appreciate the help on this.
It's the Tanks, Inc. EFI retrofit for the early A-bodies, so new tank as well (I bought the CPP kit that included tank, lines, pump, filter, etc.). In-tank 255lph pump, plumbed to the corvette filter/regulator.
Not sure what you mean by how the return is vented, but it comes back to the tank via the vette filter. I triple checked the outlets to make sure the lines went to the correct place, and the car ran great for a while before this weird no start issue and throttle/pedal errors. The tank is probably 25-30% full so when I stop cranking it sounds like the fuel is draining back through the top of the tank into the fuel.
Tank is vented to a one-way check valve at the highest spot I could find under the car. I thought about the venting issue so I took the gas cap off a couple of times with no effect (it's a non-vented cap). Also, the issue surfaced after adding fuel so the cap was open when gassing up.

I read a bit about the filters and have a Wix coming this morning so maybe I'll try that after I test the field pressure.
Again, appreciate you chiming in to help.

Old Buzzard

Let us know when you check the psi.

uwjberg

The plot thickens.
the fuel pressure gauge shows 58 pounds when the pump primes, then drops down to 10ish slowly.
when cranking, getting 58 pounds of pressure.
the car actually ran for a few seconds and then died this time. While it was running the gauge showed 58. When it stops running it holds for a couple
of seconds and then bleeds down to nothing.

I can still hear the return hose dripping fuel back into the tank after it shuts off.

I was convinced it was the filter, and now I’m having second thoughts.

G Atsma

No need to hold pressure with the engine off and pump not pumping....

uwjberg

Makes sense. That leaves me even more confused?
I have spark, fuel, air….
not sure where to go next.

Old Buzzard

"the car actually ran for a few seconds and then died this time. While it was running the gauge showed 58. When it stops running it holds for a couple
of seconds and then bleeds down to nothing".
That sounds like the engine is running off of the fuel that's supplied during the prime cycle.
It may be, the pump is not restarting after the prime cycle, thus the short run time, then the psi goes to zero.
That pump should have a check valve in it, and the regulator should hold psi for some period.
You may have lost the "run side" of the ignition.

uwjberg

Continuing to play around with the throttle body and TPS since I might at well.

Torque Pro shows throttle position at 22% when I turn the key on. Still doesn’t move when pressing the pedal. Tried the TPS re-learn procedure and it changes to 17%. Then when I crank goes right back to 22%. Also tried cranking without the throttle body plugged in and same result - sputters/starts and dies after 2-3 seconds.

uwjberg

hmm - could that be true when the fuel pressure is at 58 during cranking and also for a couple of seconds after it stops running?

In other words, I hear the pump running and see the pressure until after it stops running. Feels like the pump would stop first if there was an issue with the run side?

Ill be the first to admit I’m new at this fuel injection thing so I could be (and probably am) totally wrong.

Again, I appreciate all of the advice.

68Formula

Off topic, but pics of the Skylark?

uwjberg

still very much in patina/rat rod mode since I was focusing on the engine, suspension, etc.

68Formula

No worries, it's a cool ride. Love the old Buicks, and you don't see as many getting built.

SLWRDE

iTrader: (4)

I have a 1965 LS Swap Cutlass. Basically the Skylarks twin sister. I had a similar issue and it ended up being the Corvette style regulator. The only difference is that I had a 340 stealth pump. I switched to a Aeromotive adjustable regulator and problem solved.

uwjberg

Thanks - definitely a work in progress but I like having a car that isn't super common. Bonus is that the A bodies have a lot of parts available (although body and trim stuff is proving very hard to find).

uwjberg

Huh - I have the Wix replacement so I'll probably throw that on to see if it makes a difference. Did you do the filter/regulator combo? Where in the system did you mount it? I put mine above the rear diff trying to reduce the length of the return line. Looks like maybe the Aeromotive unit would go in the same place. They sure are proud of it though - wow.