LM7 in 1966 Skylark - DBW Issues, Now Won't Start. Help Troubleshooting?
08-15-2023, 05:51 PM
#21
TECH Resident
"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?"
Being you can hear the pump, it's likely not a "pump stop" issue.
When you try the WIX, it might be a good idea to cut the old filter apart and see what you can.
Being you can hear the pump, it's likely not a "pump stop" issue.
When you try the WIX, it might be a good idea to cut the old filter apart and see what you can.
08-15-2023, 09:11 PM
#22
Being you can hear the pump, it's likely not a "pump stop" issue.
When you try the WIX, it might be a good idea to cut the old filter apart and see what you can.[/QUOTE]
Well, put the Wix in and no difference. Cranks over, starts, then dies after a second or two.
really getting frustrated. Any other recommendations? I’d like to avoid dropping the tank if I can but I’m not even sure that will help since the pump is working and I’m getting fuel pressure?
I keep thinking the throttle/pedal codes are related somehow but it sounds like it should run even with those.
When you try the WIX, it might be a good idea to cut the old filter apart and see what you can.[/QUOTE]
Well, put the Wix in and no difference. Cranks over, starts, then dies after a second or two.
really getting frustrated. Any other recommendations? I’d like to avoid dropping the tank if I can but I’m not even sure that will help since the pump is working and I’m getting fuel pressure?
I keep thinking the throttle/pedal codes are related somehow but it sounds like it should run even with those.
08-16-2023, 12:53 AM
#23
TECH Senior Member
Has VATS been tuned out? Sounds like a classic case of it doing its job....
08-16-2023, 07:07 AM
#24
Would VATS somehow kick back in after limp mode or the PCM resetting after battery power was cut?
08-16-2023, 08:44 AM
#25
TECH Resident
VATS was turned off when I had it tuned by Mailorder Tuner and it ran great for a couple of weeks until I got the limp mode condition with the throttle/pedal position error. After I got it home it wouldn’t start again.
Would VATS somehow kick back in after limp mode or the PCM resetting after battery power was cut?
Would VATS somehow kick back in after limp mode or the PCM resetting after battery power was cut?
The following 2 users liked this post by Old Buzzard:
2ToeRacing (08-18-2023), G Atsma (08-16-2023)
08-17-2023, 08:47 PM
#26
So, I checked more wires for continuity, checked pins in the PCM for power, re-checked grounds, etc.
Same behavior of starting/coughing for a second to three or four seconds and then dying.
This time, when I was poking around the engine after it died I could hear the fuel draining out of the rails (specifically, the crossover between the two rails that has the Schrader valve on it).
The fuel pump is supposed to have a check valve on the supply line right? Seems strange to have the fuel draining from the rails back to the tank, which seems like what I've been hearing.
Pull the tank to check out the pump? I guess I'm out of other ideas.
Same behavior of starting/coughing for a second to three or four seconds and then dying.
This time, when I was poking around the engine after it died I could hear the fuel draining out of the rails (specifically, the crossover between the two rails that has the Schrader valve on it).
The fuel pump is supposed to have a check valve on the supply line right? Seems strange to have the fuel draining from the rails back to the tank, which seems like what I've been hearing.
Pull the tank to check out the pump? I guess I'm out of other ideas.
09-01-2023, 10:06 PM
#27
Well, dropped the tank and replaced the fuel pump. No difference. Starts, coughs for a couple of seconds, then dies. No pedal response when it's coughing.
I'm really running our of ideas here. Thought the check vale in the fuel pump was going to be it, but nope.
I keep going back to the fact that the only thing changed between running and driving fine and not was the limp mode and throttle/pedal position codes. I know everyone is saying it should still start and run, but nothing else changed. Really getting frustrated.
Please help before I burn this car to the ground. I was so pumped to have it driving for late summer and I'm running out of time to finally drive this thing before having to put it away for the winter.
I'm really running our of ideas here. Thought the check vale in the fuel pump was going to be it, but nope.
I keep going back to the fact that the only thing changed between running and driving fine and not was the limp mode and throttle/pedal position codes. I know everyone is saying it should still start and run, but nothing else changed. Really getting frustrated.
Please help before I burn this car to the ground. I was so pumped to have it driving for late summer and I'm running out of time to finally drive this thing before having to put it away for the winter.
09-02-2023, 06:59 AM
#28
TECH Resident
The filter line adapters we have used are adapting the filter to 3/8" AN fittings.
The Tanks Inc pump hanger has the same size fittings.
If you are using AN hose, are you sure you didn't cross the lines when you changed the pump?
That CPP "kit" may have included a knokoff Walbro pump and it died.
As an aside: In order to reduce a chance for a "crossed hoses" issue during a future filter change, we used blue hose fittings on the return and black on the pressure side. We've also used colored shrink tube on the hoses.
The Tanks Inc pump hanger has the same size fittings.
If you are using AN hose, are you sure you didn't cross the lines when you changed the pump?
That CPP "kit" may have included a knokoff Walbro pump and it died.
As an aside: In order to reduce a chance for a "crossed hoses" issue during a future filter change, we used blue hose fittings on the return and black on the pressure side. We've also used colored shrink tube on the hoses.
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2ToeRacing (09-04-2023)
09-03-2023, 09:33 AM
#29
Yeah, I labeled the lines before I removed them to make sure it was correct. In retrospect I should have gone different colors as you suggest to make it easier.
I replaced the fuel pump with a Walbro; interestingly it's significantly louder.
I have some noid lights showing up today so I can test every injector. I confirmed fuel pressure and smelled fuel when I pulled the plugs but thought it made sense to triple check.
This is the last diagnostic test I can think of....
I replaced the fuel pump with a Walbro; interestingly it's significantly louder.
I have some noid lights showing up today so I can test every injector. I confirmed fuel pressure and smelled fuel when I pulled the plugs but thought it made sense to triple check.
This is the last diagnostic test I can think of....
09-04-2023, 06:43 PM
#30
Spent a couple more hours trying to diagnose the issue. Triple checked all the fuses and grounds.
After the crank/sputter cycle a couple of times I was poking around in the engine bay and noticed that only some of the header tubes were warm.
I investigated further and only cylinders 1-7-6-4 were warm. The others were all cold. Interestingly, this means that every other cylinder is firing in order?
I confirmed that the cold cylinders are getting spark, so apparently no fuel for every other cylinder. It still will not stay running.
The only codes are still the throttle/pedal position sensor ones - no codes for mis fires.
Since it was the only sensor that wasn't brand new I threw in a new cam position sensor just to see if it helped and it made no difference.
What the heck could cause every cylinder to not get fuel?
After the crank/sputter cycle a couple of times I was poking around in the engine bay and noticed that only some of the header tubes were warm.
I investigated further and only cylinders 1-7-6-4 were warm. The others were all cold. Interestingly, this means that every other cylinder is firing in order?
I confirmed that the cold cylinders are getting spark, so apparently no fuel for every other cylinder. It still will not stay running.
The only codes are still the throttle/pedal position sensor ones - no codes for mis fires.
Since it was the only sensor that wasn't brand new I threw in a new cam position sensor just to see if it helped and it made no difference.
What the heck could cause every cylinder to not get fuel?
09-05-2023, 07:38 AM
#31
TECH Resident
"I confirmed that the cold cylinders are getting spark, so apparently no fuel for every other cylinder".
Next test is verifying the harness or ecm isn't fubar, with a NOID lite on the cold cyls.
You can pull the fuel pump fuse so the good cyls aren't hit with repeated start shots.
Next test is verifying the harness or ecm isn't fubar, with a NOID lite on the cold cyls.
You can pull the fuel pump fuse so the good cyls aren't hit with repeated start shots.
09-05-2023, 02:06 PM
#32
Yeah, the NOID light kit i ordered didn't have the right one so the new one should get here this afternoon. Hoping it will point me in the right direction.
If the injectors aren't getting a signal to fire, would that point to PCM versus harness or vis-versa? It is a new harness and everything I've checked seems good.
I took a closer look at the PCM and it turns out it's a reman unit from AC Delco (from the donor truck).
From what I've read it's not super common for a PCM to go bad and I certainly don't want to spend money on a new one plus getting it flashed again if I don't have to.
If the injectors aren't getting a signal to fire, would that point to PCM versus harness or vis-versa? It is a new harness and everything I've checked seems good.
I took a closer look at the PCM and it turns out it's a reman unit from AC Delco (from the donor truck).
From what I've read it's not super common for a PCM to go bad and I certainly don't want to spend money on a new one plus getting it flashed again if I don't have to.
10-07-2023, 07:15 PM
#33
Ok - finally got a chance to take another look.
NOID light results (in firing order):
Cylinder 1 - pulse every second for three seconds, then one every couple of seconds
Cylinder 8 - pulse every second for three seconds, then one every couple of seconds
Cylinder 7 - pulse every second for three seconds, then one every couple of seconds
Cylinder 2 - single pulse then nothing
Cylinder 6 - pulse every second for three seconds, then one every couple of seconds
Cylinder 5 - single pulse then nothing
Cylinder 4 - pulse every second for three seconds, then one every couple of seconds
Cylinder 3 - no pulse
I tried another PCM and it ran for a little longer than the original (maybe 5-6 seconds), then it dies. Now it does the same thing as the tuned PCM. Swapped the crank position sensor with a new one, and no difference.
Running out of ideas with the strange NOID results?
NOID light results (in firing order):
Cylinder 1 - pulse every second for three seconds, then one every couple of seconds
Cylinder 8 - pulse every second for three seconds, then one every couple of seconds
Cylinder 7 - pulse every second for three seconds, then one every couple of seconds
Cylinder 2 - single pulse then nothing
Cylinder 6 - pulse every second for three seconds, then one every couple of seconds
Cylinder 5 - single pulse then nothing
Cylinder 4 - pulse every second for three seconds, then one every couple of seconds
Cylinder 3 - no pulse
I tried another PCM and it ran for a little longer than the original (maybe 5-6 seconds), then it dies. Now it does the same thing as the tuned PCM. Swapped the crank position sensor with a new one, and no difference.
Running out of ideas with the strange NOID results?
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G Atsma (10-07-2023)
12-16-2023, 05:59 PM
#36
I replaced the regulator, fuel pump, throttle body, and had the PCM tested. No difference.
The plugs all looked fairly fouled and the oil smelled like gas so I changed the oil. I'll likely change the plugs this weekend.
My battery is in the trunk and I had just grounded the battery to the frame. I ran a negative cable from the battery all the way up to the block and grounded to the head.
No difference - starts, coughs for a second or two, and dies.
Hopefully I can spend some time tomorrow poking around with a multimeter but I'm no expert so I kind of don't know where to start.
Still very frustrated after what seemed to be a good start and maiden voyage.
12-19-2023, 01:36 PM
#38
Update: I spent some time over the weekend checking on stuff and I was able to get it started. The only difference was adding an alligator clipped ground wire from the TAC module to the chassis (it had been sitting on the floorboard previously). Somehow or another that let me clear the DBW codes and get it started. I'd read and been told over and over that the motor should start with the pedal disconnected, the codes I had, etc. but it looks like that somehow didn't apply to my set up?
I also have no idea why grounding the TAC would make a difference now because when it was running before I was able to start, run, and drive before the limp mode at WOT. Very strange.
I took it for a drive and while it idles and revs just fine it's pretty rough under load at partial throttle and was bucking quite a bit (didn't do that before). I'm going to throw new plugs in just in case my efforts to start it over the last few months fouled them out.
I also have no idea why grounding the TAC would make a difference now because when it was running before I was able to start, run, and drive before the limp mode at WOT. Very strange.
I took it for a drive and while it idles and revs just fine it's pretty rough under load at partial throttle and was bucking quite a bit (didn't do that before). I'm going to throw new plugs in just in case my efforts to start it over the last few months fouled them out.