88 truck, runs great with the map unplugged

[lickmyburger89]

I've been chasing this issue for a little while, the truck will start and die as soon as it turns over. stays running if you give her some throttle but will die as soon as she tries to idle.sounds fine when you rev with no load. misses and runs like crap taking off. unplug the map,she runs beautifully. running rich that way but no issues and has 18in of vacuum at the map port. if i plug in the map while running she'll die right away and it looks almost as if the injectors get cut off right before she dies . I've tested the injectors, coolant temp sensor, tps, map, iac, egr solenoid,egr and passages, o2, fuel relay, and oil pressure switch which all test out fine. fuel pump was weak so i replaced it and the filter, and reuilt the throttle body because of a leaky regulator. replaced the distributor because of a failed coil pickup and replaced plugs and wires too. Is there anything i could have overlooked before i put blame onto the ecm?

 

[lickmyburger89]

so i hooked obd1 scan tool to see what it would come with and came up with much more codes than what jumping pins did. just jumping the pins, i got the map circuit low and rich codes like i expected, but the scan tool brought up 42 est open or shorted, 33 map voltage high,32 map voltage low, 31 park/neutral switch, 55 ecm or 02 fault, 54 fuel pump circuit or ecm fault/egr solenoid #2 failure, 52 calibration chip or ecm fault, and last was 43 est circuit low voltage. it does have a different engine in it and the previous owner told me the original ecm is in it. is this enough to condemn the ecm?

 

[skylark]

Clear the codes and try again. All of the unplugging will cause the map codes, the o2 codes is because it is rich and the est code is from setting the timing.

 

[lickmyburger89]

i'll clear codes and she'll read no codes jumping the terminals but the codes read off of the scan tool remain the same

 

[Schurkey]

"I" would be suspecting a failed MAP sensor or MAP wiring harness.

Instead of looking for "codes", look at the data stream. What is it showing for manifold vacuum? What are the short- and long-term fuel trims? What is the actual idle speed vs. commanded idle speed? Coolant temperature?

The answer(s) you're looking for are almost certainly in the data stream.

 

[RichLo]

Does OBD1 have data logging capabilities?

 

[lickmyburger89]

no data stream or loggingcapabilities with this cheapo scan tool for obd1. its an innova 3120d. Bought it cheap for obd2 crap and it had the extra perk of giving obd1 codes so i wouldn't have to look it up. A guy on gearhead-efi told me the scan tool probably generated the codes by itself if it didn't match flashing codes jumping the terminals. have messed with different years of obd1 trucks to scan and if i remember right, the years that gave the right info were if i remember right, 92 and 95 model year options. i just may bring that up in that forum because i'm curious about it, especially with the motor being replaced and claimed not have had the ecm changed out as well.

 

[lickmyburger89]

any recommendations for a bidirectional obd1 scan tool?

 

[koolbreeze]

You can grab a cable from Moates (or build one) and connect laptop running TunerPro RT to it to view the live data stream. You'll need to check which ECM you have and get the matching ADX file as well.

https://www.moates.net/gm-19851995-c-64.html

Edit:
You'll need at least the ALDU1 and a CABL1 or CABL2 (depending on which port you have). You can see the difference here:
http://support.moates.net/aldu1/

 

[lickmyburger89]

Thanks for the info on that. actually a fairly interesting setup. definately the CABL1 on my truck. i'm about to go out and check to see which prom is in the truck.