Stalling When Pulling Away From a Stop

[Machlen]

As a reminder/note: the truck only dies when pulling away from a stop, not while idling at the stop.

I can lift my foot off of the brake while in drive and allow the car to roll forward to 3-5mph naturally in D and it will not stall. It’s once I begin to press the accelerator pedal that the truck stalls.

 

[GoToGuy]

Dead spot in TPS ?

 

[L31MaxExpress]

From the description it sounds like it is EGR related.

 

[Schurkey]

I borrowed a basic GM OBD1 reader... ...Will plug it in tomorrow and see if any useful codes come out of it.

A "code reader" is a useless waste of time, money, effort, and enthusiasm on OBD1 vehicles.

You need a scan tool, not a code reader.

 

[Machlen]

From the description it sounds like it is EGR related.

I pulled the vacuum line off of the EGR valve and tested it by hand: block the vacuum port with my thumb and pressed in the diaphragm. The EGR valve held a perfect vacuum seal and the diaphragm did not expand back down until I released my thumb from the vacuum port on the EGR valve. Do you think this rules out it being an EGR issue? The valve seems good unless my testing is flawed…

A "code reader" is a useless waste of time, money, effort, and enthusiasm on OBD1 vehicles.

You need a scan tool, not a code reader.

OK - I will need to rent a scan tool from somewhere then, if possible. I don’t have the ability to invest in such a tool currently. The basic OBD1 code reader did read out a couple codes:

13: Oxygen sensor signal fault - signal too low / open left oxygen sensor circuit (Dual sensor models)

43: Electronic spark timing (EST) circuit - low voltage detected OR Electronic spark control (ESC) - circuit problems.

However, I don’t think either of this are the root cause of my issue.

 

[L31MaxExpress]

I pulled the vacuum line off of the EGR valve and tested it by hand: block the vacuum port with my thumb and pressed in the diaphragm. The EGR valve held a perfect vacuum seal and the diaphragm did not expand back down until I released my thumb from the vacuum port on the EGR valve. Do you think this rules out it being an EGR issue? The valve seems good unless my testing is flawed…


OK - I will need to rent a scan tool from somewhere then, if possible. I don’t have the ability to invest in such a tool currently. The basic OBD1 code reader did read out a couple codes:

13: Oxygen sensor signal fault - signal too low / open left oxygen sensor circuit (Dual sensor models)

43: Electronic spark timing (EST) circuit - low voltage detected OR Electronic spark control (ESC) - circuit problems.

However, I don’t think either of this are the root cause of my issue.

Your testing is flawed. It should not hold vacuum on the TBI era valve. The vacuum is bled off by a valve internal to the EGR to help control it. My quick test is to unplug the valve, plug the vacuum line and take it for a drive. If it runs better with the EGR disabled, I dig into it further.

 

[Machlen]

Your testing is flawed. It should not hold vacuum on the TBI era valve. The vacuum is bled off by a valve internal to the EGR to help control it. My quick test is to unplug the valve, plug the vacuum line and take it for a drive. If it runs better with the EGR disabled, I dig into it further.

Ok, that’s good to know. Thanks for the reply, I will try that tomorrow! Just to be clear - I can leave the EGR valve mounted in its spot, simply unplug the vacuum line from the EGR valve and plug the end of the line with something and test drive? Thanks again.

 

[L31MaxExpress]

Ok, that’s good to know. Thanks for the reply, I will try that tomorrow! Just to be clear - I can leave the EGR valve mounted in its spot, simply unplug the vacuum line from the EGR valve and plug the end of the line with something and test drive? Thanks again.

Yes sir, done it numerous times. When the EGR valve acts up, it goes to full EGR opening nearly the instant the EGR solenoid enables it. At low rpm it can cause a vicous stumble, surging or even stall.

 

[RichLo]

In my experience when an EGR goes bad, it will not idle.

I second the TPS idea

 

[Machlen]

Yes sir, done it numerous times. When the EGR valve acts up, it goes to full EGR opening nearly the instant the EGR solenoid enables it. At low rpm it can cause a vicous stumble, surging or even stall.

Alright awesome, will give that a try and report back. Thank you and fingers crossed!

In my experience when an EGR goes bad, it will not idle.

I second the TPS idea

Would a faulty TPS result in only having issues when pulling away from a complete stop though? I feel like a faulty TPS would be a more persistent issue, including when on the freeway, no?