1989 gmc has me running circles - The 1947 - Present Chevrolet & GMC Truck Message Board Network

radiatorrepair · 02-04-2015, 04:22 PM

Hello,
I am new to this and will appreciate any help/information you men on here are wiling to give. I rarely run into anything that absolutely alludes me, but this one is and I know it has got to be something simple. I have a 1989 gmc with 5.7 TBI, parked it one day, got in and it was running real rough, idle, for a second, surge up an down once or twice and die, like it hasa vacuum leak or lean fuel. I hae canged fel pump, and yes the hose that connects the pump to the pickup tube, new fuel filter, new O-2 sensor, MAP sensor, TPS, Heat sensor, Control module, new gaskets and fuel pressure regulator in he TBI , cleaned and reattached all the grounds, checked the plugins on the ECM, and replaced the IAC valve, alo checked the EGR and it was clean, no vacuum leaks to the brake booster ect. Could it bethe distributor or the ECM? It surges at idle, if I pump the pedal, can get it to rev, once the rpms are up runs smooth, I did spay carb cleaner around te intake ect., no change.
There has to be something I am missing.
Thanks ahead of time.

Mr_Shamrock · 02-04-2015, 08:48 PM

Sounds like a bad IAC or carboned up IAC passage. Did you clean/inspect that area when you had the TB off? Also just because the EGR is clean doesn't mean it isn't leaking vacuum. Test it to make sure the diaphram is good and will hold vacuum. Check fuel pressure, I know you replaced the pump, but new doesn't necessarily mean good anymore.

radiatorrepair · 02-04-2015, 11:05 PM

Yes, sir, I completely cleaned the IAC passage and replaced the IAC itself, fuel pressure while running is almost 15lbs. The EGR does leak vacuum a little, but it is still doing the same even when the vacuum line is plugged off that goes to it and the EGR is free and not stuck open.

Mr_Shamrock · 02-04-2015, 11:24 PM

Plugging the EGR port won't help if the EGR itself is leaking vacuum. You could do a cheap test and take a soda can (or anything similar) and block the EGR off at the intake. You can cut the pattern easily out of a soda can and install it under the EGR valve. Do that and cap the port on the TB and that will 100% rule out that circuit. The TBI trucks are very finicky with the EGR valves. I have also had the coolant temp sensor (by the thermostat) cause issues without throwing a code. There is an ohm test you can run on them.

radiatorrepair · 02-05-2015, 12:35 AM

I will try the trick with the egr, I already replaced the coolant temp sensor and the wires to it. Thank you.

Mr_Shamrock · 02-05-2015, 12:16 PM

Just thought of something else that I recently came across - make sure the wires going to the injectors haven't been rubbed/worn through by the air cleaner spacer. Also make sure you have a consistent spray pattern on both injectors. My 95 just experienced the rub through on the wires while I was sitting at a light. It stumbled real bad and died. It fired back up and surged up and down a few times and then ran ok the rest of the way home. I just happened to catch one injector stop spraying for a few seconds when I pulled the air cleaner for inspection. I haven't replaced the wires yet, but pulled them away from the spacer and taped up the bare spot on the wire and it has been fine.
Just another idea.

radiatorrepair · 02-05-2015, 06:47 PM

Thank you for all the help with diagnosing this thing, I did find out that it was the distributor, finaly as I was holding it at about 2000 rpm it stopped firing, pulled the distributor and the pickup inside was catching as I turned it, put in a new one, now seems to run fine., was kinda odd, sure was acting like a fuel issue, not a spark.

mountie · 02-09-2015, 11:04 PM

Quote:

Originally Posted by radiatorrepair

Thank you for all the help with diagnosing this thing, I did find out that it was the distributor, finaly as I was holding it at about 2000 rpm it stopped firing, pulled the distributor and the pickup inside was catching as I turned it, put in a new one, now seems to run fine., was kinda odd, sure was acting like a fuel issue, not a spark.

Your situation sounded similar to what I went through almost a year ago...

But, after changing all those parts, THEN discovering the culprit, NOW, it runs great, with all the new stuff !!

02-04-2015, 04:22 PM	#1
radiatorrepair Registered User Join Date: Feb 2015 Location: Stillwater, Oklahoma Posts: 7	1989 gmc has me running circles Hello, I am new to this and will appreciate any help/information you men on here are wiling to give. I rarely run into anything that absolutely alludes me, but this one is and I know it has got to be something simple. I have a 1989 gmc with 5.7 TBI, parked it one day, got in and it was running real rough, idle, for a second, surge up an down once or twice and die, like it hasa vacuum leak or lean fuel. I hae canged fel pump, and yes the hose that connects the pump to the pickup tube, new fuel filter, new O-2 sensor, MAP sensor, TPS, Heat sensor, Control module, new gaskets and fuel pressure regulator in he TBI , cleaned and reattached all the grounds, checked the plugins on the ECM, and replaced the IAC valve, alo checked the EGR and it was clean, no vacuum leaks to the brake booster ect. Could it bethe distributor or the ECM? It surges at idle, if I pump the pedal, can get it to rev, once the rpms are up runs smooth, I did spay carb cleaner around te intake ect., no change. There has to be something I am missing. Thanks ahead of time.

02-04-2015, 08:48 PM	#2
Mr_Shamrock Registered User Join Date: Feb 2014 Location: Greenville, SC Posts: 63	Re: 1989 gmc has me running circles Sounds like a bad IAC or carboned up IAC passage. Did you clean/inspect that area when you had the TB off? Also just because the EGR is clean doesn't mean it isn't leaking vacuum. Test it to make sure the diaphram is good and will hold vacuum. Check fuel pressure, I know you replaced the pump, but new doesn't necessarily mean good anymore. __________________ LifeTime GM guy. Current collection... 2006 Z-71 Suburban 1985 C-10 1990 Suburban 1966 C-10 (me & dad's project)

02-04-2015, 11:05 PM	#3
radiatorrepair Registered User Join Date: Feb 2015 Location: Stillwater, Oklahoma Posts: 7	Re: 1989 gmc has me running circles Yes, sir, I completely cleaned the IAC passage and replaced the IAC itself, fuel pressure while running is almost 15lbs. The EGR does leak vacuum a little, but it is still doing the same even when the vacuum line is plugged off that goes to it and the EGR is free and not stuck open.

02-04-2015, 11:24 PM	#4
Mr_Shamrock Registered User Join Date: Feb 2014 Location: Greenville, SC Posts: 63	Re: 1989 gmc has me running circles Plugging the EGR port won't help if the EGR itself is leaking vacuum. You could do a cheap test and take a soda can (or anything similar) and block the EGR off at the intake. You can cut the pattern easily out of a soda can and install it under the EGR valve. Do that and cap the port on the TB and that will 100% rule out that circuit. The TBI trucks are very finicky with the EGR valves. I have also had the coolant temp sensor (by the thermostat) cause issues without throwing a code. There is an ohm test you can run on them. __________________ LifeTime GM guy. Current collection... 2006 Z-71 Suburban 1985 C-10 1990 Suburban 1966 C-10 (me & dad's project)

02-05-2015, 12:35 AM	#5
radiatorrepair Registered User Join Date: Feb 2015 Location: Stillwater, Oklahoma Posts: 7	Re: 1989 gmc has me running circles I will try the trick with the egr, I already replaced the coolant temp sensor and the wires to it. Thank you.

02-05-2015, 12:16 PM	#6
Mr_Shamrock Registered User Join Date: Feb 2014 Location: Greenville, SC Posts: 63	Re: 1989 gmc has me running circles Just thought of something else that I recently came across - make sure the wires going to the injectors haven't been rubbed/worn through by the air cleaner spacer. Also make sure you have a consistent spray pattern on both injectors. My 95 just experienced the rub through on the wires while I was sitting at a light. It stumbled real bad and died. It fired back up and surged up and down a few times and then ran ok the rest of the way home. I just happened to catch one injector stop spraying for a few seconds when I pulled the air cleaner for inspection. I haven't replaced the wires yet, but pulled them away from the spacer and taped up the bare spot on the wire and it has been fine. Just another idea. __________________ LifeTime GM guy. Current collection... 2006 Z-71 Suburban 1985 C-10 1990 Suburban 1966 C-10 (me & dad's project)

02-05-2015, 06:47 PM	#7
radiatorrepair Registered User Join Date: Feb 2015 Location: Stillwater, Oklahoma Posts: 7	Re: 1989 gmc has me running circles Thank you for all the help with diagnosing this thing, I did find out that it was the distributor, finaly as I was holding it at about 2000 rpm it stopped firing, pulled the distributor and the pickup inside was catching as I turned it, put in a new one, now seems to run fine., was kinda odd, sure was acting like a fuel issue, not a spark.



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