Brown timing wire diesafter unplugged

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87squareHayes

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1987 gmc v1500 5.7 tbi. Trying to set timing. Everytime I unplug the brown timing advance wire, it goes dead. I've tried advancing the timing, but still does it. Tried new coolant temp sensor, new IAC, plugs, wires, cap, button, checked all fuses.. Can't seem to keep it running. Just dies. Doesn't even hesitate. Bought the truck 6 months ago. Was told it was rebuilt 2 yrs ago. Don't run awful but hesitation when first acceleration and spits out the tbi every now and again. First squarebody with having a tbi. So kinda new to me. Any help would be appreciated.
 
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when you unplug the timing wire, the timing should be controlled by the ignition control module under the cap. if it just dies when you unplug the timing wire, I'd suspect that the module may be bad or maybe is somehow poorly grounded?

check the reference library for the service manuals. the emissions and drivability manual is critical to TBI troubleshooting, along with ALDLDroid on an android device and a Bluetooth OBD1 cable to function as a scan tool.
 
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Is the base idle set? Need to have data access to get IAC counts. Anything from a partially stuck open EGR to a vacuum leak could cause that. Computer has the ability to adjust within certain parameters these issues crop up when those capabilities are exceeded.
 
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gmbellew

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good call on checking for vacuum leaks and EGR system operation.

if you replaced the IAC, you could try a hard IAC reset by jumpering AB on the ALDL port with a paper clip with ign on for about 45sec. that will fully seat it and the computer knows where closed is regarding IAC counts.
 
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87squareHayes

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5.7 tbi
gmbellew said:
when you unplug the timing wire, the timing should be controlled by the ignition control module under the cap. if it just dies when you unplug the timing wire, I'd suspect that the module may be bad or maybe is somehow poorly grounded?

check the reference library for the service manuals. the emissions and drivability manual is critical to TBI troubleshooting, along with ALDLDroid on an android device and a Bluetooth OBD1 cable to function as a scan tool.
Click to expand...

gmbellew said:
when you unplug the timing wire, the timing should be controlled by the ignition control module under the cap. if it just dies when you unplug the timing wire, I'd suspect that the module may be bad or maybe is somehow poorly grounded?

check the reference library for the service manuals. the emissions and drivability manual is critical to TBI troubleshooting, along with ALDLDroid on an android device and a Bluetooth OBD1 cable to function as a scan tool.
Click to expand...
Thank you. I just ordered another control module and I'll be putting it on Wednesday to see if that works. I'll also check the ground too and see if it's grounded good.
 
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87squareHayes

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fast 99 said:
Is the base idle set? Need to have data access to get IAC counts. Anything from a partially stuck open EGR to a vacuum leak could cause that. Computer has the ability to adjust within certain parameters these issues crop up when those capabilities are exceeded.
Click to expand...
I was told to get the timing right first before troubleshooting the base idle. Should I look at that first?
 
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87squareHayes

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gmbellew said:
good call on checking for vacuum leaks and EGR system operation.

if you replaced the IAC, you could try a hard IAC reset by jumpering AB on the ALDL port with a paper clip with ign on for about 45sec. that will fully seat it and the computer knows where closed is regarding IAC counts.
Click to expand...
I will be working on it again Tuesday and do a reset for the iac. Got another EGR on the way because the other on it looks old so going to put another on there then test. Thanks
 
fast 99

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Normally the timing would be set or checked first. Problem your having is you have no idea where the IAC counts are. If they are at either limit the EMC cannot control idle. Really need to try to diagnose rather than tossing more parts at it. Could you imagine paying a shop for this kind of work? Ricko1966 had a post a few days ago describing exactly what you're doing. May be someone could find it, I was unable.
 
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87squareHayes

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fast 99 said:
Normally the timing would be set or checked first. Problem your having is you have no idea where the IAC counts are. If they are at either limit the EMC cannot control idle. Really need to try to diagnose rather than tossing more parts at it. Could you imagine paying a shop for this kind of work? Ricko1966 had a post a few days ago describing exactly what you're doing. May be someone could find it, I was unable.
Click to expand...
Thank you. I'll try and find it.
 
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fast 99 said:
Normally the timing would be set or checked first. Problem your having is you have no idea where the IAC counts are. If they are at either limit the EMC cannot control idle. Really need to try to diagnose rather than tossing more parts at it. Could you imagine paying a shop for this kind of work? Ricko1966 had a post a few days ago describing exactly what you're doing. May be someone could find it, I was unable.
Click to expand...
Here ya go...

Diagnose 1st Replace parts second

This isn't aimed at anyone so nobody take it personal. It's just good advice. So a post goes up. Getting bad milage, runs horrible I changed my carbureator twice,put on a FP regulator, 1st one leaked so installed another one, still runs bad, I replaced my cap,rotor,wires,now runs like...
www.gmsquarebody.com www.gmsquarebody.com
 
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