Surging problem and cause

[kevinde1]

Sorry can you explain to me a little better where that connector is? what color are the wires? I don't know where the governor is lol. I found the the green vss buffer and also found a bunch of melted wires coming off the headlight switch :/

 

[1987 GMC Jimmy]

Sorry can you explain to me a little better where that connector is? what color are the wires? I don't know where the governor is lol. I found the the green vss buffer and also found a bunch of melted wires coming off the headlight switch :/

Sorry about that. Here you go. Just scroll down a little bit for pictures.
http://www.gmsquarebody.com/forum/showthread.php?t=17245&highlight=700r4+lockup

 

[farmerchris]

brother had a 87 Blazer,5.7tbi with similar surging problems,go up and down in idle,actually got where it would shut down, when restart was alright for awhile.we chased down the the esc circuit on his truck, change out the computer(ecm),traded out chips in computer.new coolant switches(cts)rebuild throttle body,think he traded throttle bodies for a known good one.changed out several ignition module. final cure was a replacement distributor.tries aftermarket ones and junkyard ones,no luck.went to get a original one it was off the parts books(discontinue)Had a good parts man and he found it in gmperformanceparts catalog .part #1103952,factory replacement,work like a charm ,no more issuses,he's happy with his Blazer again.

 

[kevinde1]

Well yesterday I chased out a melted wire that turned out to be the tail lights wire off of the headlight switch I had to unwrap the wires and pull them apart and get that bad wire outta there, went ahead and checked the rest of them, looks ok now. I changed the ECM, MAP, CTS, TPS and ESC still no change, it does have a newer aftermarket distributor with a brand new AC DELCO ICM. I'm back to square one, the only idea I have left is maybe it has jumped timing. A buddy of mine was helping me yesterday and he was watching the injectors when we applied the 20hg to map sensor he said injectors never stopped pulsing and that seems more like it flooding the truck and killing it. I'll have to check into that. TCC voltage is way low at the ECM but other than that the rest are OK. I have one chart that says that MAP voltage should be 2.0v and another that says at 20hg it should read 1.1v which I have tested 2 MAPs now and they are both 1.1v at idle but for some odd reason that kills the motor.

 

[kevinde1]

anybody have thoughts on possibly a bad PROM?

 

[wczimmerman]

I am following this closely for a solution...keep up the great work!

 

[1987 GMC Jimmy]

anybody have thoughts on possibly a bad PROM?

Sorry this has sat unanswered for so long. You should get a Code 51 if the PROM was bad. Even if the PROM was bad, the CALPAK would take over. It'd run rich and not the best, but it'd still be stable. Do you have any updates? This bothers me that the issue hasn't made itself apparent as of yet. In times of desperation, I say make a scan tool. Here's how.

http://www.gmsquarebody.com/forum/showthread.php?t=13194

Also, how's the ground strap from the cylinder head to the firewall on the passenger side? My brother had a hard Code 22 for low TPS voltage, and once he replaced his trashed ground strap, it went away for good.

 

[VAL]

I had a surging issue on my 1990 c1500 TBI, which is basically the same as the 87. I spent months trying to find the solution, it turned out to be the temperature sensor. Not the one on the side of the engine block, but the one that sits right in front of the thermostat. I changed it out and no more surging.

 

[1987 GMC Jimmy]

I hear you. That's one of the first things I would have suggested, but he said he changed it. Granted, it may have been bad from the get go, but that can be any aftermarket part at any time that's already been installed on the truck. Either way, the CTS should be changed every once in a while on a GM TBI or CCC car or truck because they seem to fail gradually over time anyways. I suggested the scan tool so maybe he can see his sensor feedback and see if something's wrong there. I feel bad when an issue's brought up here with a vehicle and a lot is exhausted with no results.

 

[kevinde1]

My ground strap is good I even added a second one to be sure. My CEL works and I don't get any codes unless I unplug something. I tried a new distributor this last weekend and no change. It wasn't an AC Delco those things are 400+$. I've replaced the temp sensor twice. TPS, ESC, ECM still no change. Im checking the timing chain this weekend. My MAP sensor voltage output is 1.1v and I've had 3 different ones I've tried. The FSM says it should be at 2.0v I've seen other charts says it should be at 1.1v, so since I've had 3 different ones on there and still at 1.1v I'm gonna say that's probably where it needs to be but the truck just won't stay running. In the beginning I thought injectors stop pulsing but I think they are just leaning out. So all my voltages look good at the ECM except the TCC and I'm going to check into that hopefully it needs fluid it does have a pan leak. Cam gear looks good no play at the distributor. I have a feeling it has a lot of slack in the timing chain or it has jumped time a little. I've only had this truck a few weeks so I don't know what all it's been through. I have read multiple post of surging and they change a temp sensor or distributor find a vacuum leak and are good to go but there are others who have replaced every sensor cleaned every ground and never report back if it was fixed. Luckily the previous owner did the sensors I've changed a few and glad the parts store let me return them. I could be wrong but I believe it's a mechanical issue at this point we'll find out this weekend thanks for the all the input and advice, much appreciated. Hopefully I will get to the bottom of this problem and help the next guy out.

 

[1987 GMC Jimmy]

Are you gonna use a timing light to see if you're timing mark is all over the place, or are you gonna turn the crank by hand to check for slop in the rotor turning? A great tool that tells you a whole lot more than you'd think about the mechanical state of your engine is a vacuum gauge, too. Maybe pick one up and see what your idle vacuum is and see if the needle's behaving erratically.

 

[kevinde1]

Well I'm glad you posted that chart, my engine pulls a steady 20 to 21hg at 650 to 700 rpm. I was watching my timing mark with the timing light the other day it was running at about 8 degree advanced and just like a switch flipped it dropped to about 4 degree. My distributor gear looks good and I really can't feel any play in the distributor.

 

[kevinde1]

What kind of readings do ya'll get at the MAP sensor output? It seems if I had an adjustable MAP sensor I could set it at 2v at idle and would be good to go, but who knows. I just can't seem to let this MAP sensor thing go until I find out what the correct reading is supposed to be. Maybe my injectors are not flowing well at the low RPM?

 

[Georgeb]

I have this....

 

[kevinde1]

OK well according to that I'm right on the money as far as volts are concerned.