djackson210
Contributor
Posts: 213
Age: 41
Loc: San Antonio, Texas
Reg: 01-31-19
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09-19-24 05:55 AM - Post#2874010
In response to Shepherd
Based on his road test, seems not fixed. Need the cel code for further evaluation.
It was a code 34. I followed all the troubleshooting information from the service manual & it says the sensor is fine. So it could be an electrical issue, my favorite. :sad :
'91 Chevy C1500 2WD
'89 Suburban 4WD
'92 GMC Sierra 2WD |
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djackson210
Contributor
Posts: 213
Age: 41
Loc: San Antonio, Texas
Reg: 01-31-19
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09-19-24 09:22 AM - Post#2874012
In response to djackson210
Still no dice. Tried to take it for another test drive this morning. Barely made it into the turn lane before it crapped the bed again. CEL came back on. Code 33, 34 & 42. So yeah, I'm stumped.
'91 Chevy C1500 2WD
'89 Suburban 4WD
'92 GMC Sierra 2WD |
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 Shepherd
Valued Contributor
Posts: 3536
Loc: Lake George, NY
Reg: 11-11-15
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09-19-24 11:03 AM - Post#2874014
In response to djackson210
Pcms/ecus, were somewhat problematic during that period, all else failing here, possible the ecu is misinterpreting the info and is the root cause.
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djackson210
Contributor
Posts: 213
Age: 41
Loc: San Antonio, Texas
Reg: 01-31-19
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09-25-24 09:47 AM - Post#2874187
In response to Shepherd
I haven't given up on figuring this turd out. I had to take a break from it though, it was frustrating me to the point where I was ready to sell the whole rig for $2K just to get it out of here.
I started it up today & it still idles pretty damn good, no black smoke getting belched out of the tail pipe. But my snap-on scanner is reading 0.02v at the MAP sensor with the truck idling. I know that isn't right so I'm still trying to hunt down the issue with the MAP. I believe that's where all my issues are stemming from.
I'll report back when I have any new updates. It might take me a week or so. But I'll report back either way, even if I give up & sell it.
'91 Chevy C1500 2WD
'89 Suburban 4WD
'92 GMC Sierra 2WD |
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Shepherd
Valued Contributor
Posts: 3536
Loc: Lake George, NY
Reg: 11-11-15
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09-25-24 01:12 PM - Post#2874197
In response to djackson210
The reference voltage to the map is .5v, are you reading that or the signal back to the ecu? What barometer reading are you getting?
Edited by Shepherd on 09-25-24 01:16 PM. Reason for edit: No reason given.
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djackson210
Contributor
Posts: 213
Age: 41
Loc: San Antonio, Texas
Reg: 01-31-19
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09-25-24 01:32 PM - Post#2874202
In response to Shepherd
The reference voltage to the map is .5v, are you reading that or the signal back to the ecu? What barometer reading are you getting?
I'm following the service manual for an '89 TBI vehicle. When I follow the trouble tree for a Code 34 it tells me that I've got a faulty connection or sensor.
By barometer reading do you mean that pressure number from the scanner?
I checked the Gray 5v reference wire all the way to the ECM for continuity, it's fine. Not broken anywhere along the way. I made sure that neither of the other 2 wires were broken or grounded, they're good too. So all the wires to the MAP sensor are intact.
Here's the weird thing. With the new NTK MAP sensor the truck will not belch black smoke out the tailpipes, but it sets a code 34. With the original MAP sensor, it's belches smoke but doesn't set a code 34.
I was just messing around with the timing, manually turning the distributor to where the truck leveled out & stopped belching smoke with the original MAP sensor. So I let it get up to operating temp, shut off the truck, unplugged the timing advance wire, set to TDC, turned the truck off, plugged the advance wire back in, started the truck & it idles like crap & belches black smoke.
I beginning to think I have an issue with the ECM because none of this is making sense to me. I can't get it to give me a consistent problem across the board.
'91 Chevy C1500 2WD
'89 Suburban 4WD
'92 GMC Sierra 2WD |
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Shepherd
Valued Contributor
Posts: 3536
Loc: Lake George, NY
Reg: 11-11-15
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09-25-24 05:08 PM - Post#2874212
In response to djackson210
I assume you have checked vacuum at the map? Retarded timing would cause low vacuum and a rich mixture.
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djackson210
Contributor
Posts: 213
Age: 41
Loc: San Antonio, Texas
Reg: 01-31-19
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10-01-24 09:45 AM - Post#2874340
In response to Shepherd
I assume you have checked vacuum at the map? Retarded timing would cause low vacuum and a rich mixture.
There was a section of the service manual that did require me to check vacuum at the MAP sensor. The MAP sensor checks out. But it's still possible that's the culprit.
'91 Chevy C1500 2WD
'89 Suburban 4WD
'92 GMC Sierra 2WD |
|
djackson210
Contributor
Posts: 213
Age: 41
Loc: San Antonio, Texas
Reg: 01-31-19
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10-01-24 09:55 AM - Post#2874341
In response to djackson210
So I took a break from it for a week, just let it sit there with the battery disconnected.
I went out there 30 minutes ago & started it. It was idling fine. After about 5-10 minutes the RPM's dropped like they're supposed to once the engine begins to warm up. It hasn't done that during this whole ordeal. The RPM's have consistently stayed at 1K while idling, even once it's hot.
But that didn't last for very long, then the RPM's came back up to 1K, then for a few minutes they even crept higher than that. Getting up to about 1,300RPM, I was ready to kill the engine if the RPM's kept climbing, but they settled back down to 1K.
I'm still getting a small amount of black smoke out of the tail pipes. I can adjust for that by rotating the dizzy, almost like an engine with a carb. So I believe I've still got an issue with the timing somehow.
Let's put the black smoke/timing aside for a bit. I'd like to figure out why the RPM's won't come off 1K even once fully warm.
I was under the impression that the ECT Sensor is what sort of controlled the RPM's. In the sense that it tells the computer what the coolant temperature is so it can then bring the RPM's down to a reasonable level once it's warmed up. That's how this truck used to run & how my other 3 TBI engines run. "High" idle for the first few minutes then it settles down as the engine gets warm.
What else could be causing the engine RPM's to stay at 1K & above? TPS sensor, vacuum leak? Any pointers is greatly appreciated.
'91 Chevy C1500 2WD
'89 Suburban 4WD
'92 GMC Sierra 2WD |
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 gchemist
Member #271 Senior Chevytalk Moderator
Posts: 26110
Loc: Austin, TX 78748
Reg: 05-09-00
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10-02-24 04:03 AM - Post#2874361
In response to djackson210
Are both temp sensors fairly new? A vacuum leak will cause high idle. Spray some WD-40 around the TBI base. If idle changes, the gasket is probably bad.
Does timing jump around? Did this year still have the nylon timing gear?
'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE
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