Engine started running rough 350 TBI - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Patsfan34 · 10-03-2010, 04:22 PM

I bought an 87 GMC 4x4 2500 about a month ago. Was sitting for a handful of years in a barn at a local farm. I got a great deal on it and knew I could fix most of the stuff it needed. It's said to have 73K original miles.

First what i fixed or replace: new exhaust (cat back), new shocks, full tune up (plugs, wires, cap, rotor, air filter), radiator and heater hoses, all 3 belts, coolant flush and new coolant. Radiator had a tiny hole in the center so I bought some stop leak and it immediately stopped leaking. I also changed the power steering pump. i didn't buy a new one cause an engine I had in my garage still had one that I knew worked fine. I was having problems with the starter (it would only catch every other time) so i pulled it out and noticed the teeth were pretty chewed up. I actually had another starter hanging around out of the donor truck for my project so I compared them and they looked the same (different model numbers) but I bolted it in and the truck turned over perfect.
I figured it was time to take the truck for a ride to see how it ran. I took it out last Sunday and drive it around for about 30 minutes and it was flawless. This was before I switched the starter and it ran great, sounded great. This Wednesday after I finished with the starter swap I took it for another ride only 5 minutes and when I got home it was running terrible. It will not idle. When I turn it over it starts right up but I have to give it gas to keep it running or it will shut off. Could the starter have caused the problem? I checked everything again hoping maybe a ground came loose but nothing.

I pulled the air cleaner off to inspect the TB and I noticed the plugs seem to have melted a bit. Pic below. Obviously I am going to replace them. What could have cause these things to melt? I've had the air cleaner off a handful of times but never noticed the plastic on the plugs melted. When I started the truck today a massive cloud of white exhaust came out of the tailpipe and it was like that for about 30 seconds but then eventually cleared out. Sorry for the long post but I wanted you guys to have all the info. I even pulled the exhaust again just to make sure the cat wasn't clogged and nothing. Any help is appreciated!

Thanks, Patsy

Patsfan34 · 10-03-2010, 06:43 PM

^^^

BigBlocksRule · 10-04-2010, 07:32 AM

If the coolant temp sender is out, it will tell the computer that intake coolant is -150 degrees or so, so the computer richens up the mix quite a bit. That'll make 'em idle rough, if they'll run at all. Good thing is you can unplug the old one and plug a new one in and just let it rest on the intake manifold to test it.
White smoke is generally from water/coolant, but could be from a number of things. Check for bubbles in the radiator when the truck is idling...

Patsfan34 · 10-04-2010, 09:16 AM

That temp sender is on the drivers side of the engine block right? When I did the tune up I remember disconnecting the wire on that side. I did hook it back up but I will give it a shot. This is the first time I ever seen white smoke come out of this truck. It cleared out after about 30 seconds. Thanks BigBlock.

RandyP · 10-04-2010, 09:37 AM

No, the temp sensor is by the water neck on the intake.

BigBlocksRule · 10-04-2010, 01:00 PM

^ what he said, it's right up front. The one in the driver's head is for the gauge or idiot light.

Patsfan34 · 10-04-2010, 10:18 PM

wow good thing I asked! Thanks guys. I will get parts tomorrow and work on it Wednesday.

BigBlocksRule · 10-04-2010, 10:21 PM

Unplug the one on the engine and plug it into your replacement without taking anything out of the intake, just leave the new one laying on the intake. If it is the intake coolant temp sensor that's bad, the truck will run better pretty much immediately. If it doesn't help, there's no need to replace it, just hang onto it for a spare for when it does need replacement.

Patsfan34 · 10-04-2010, 10:29 PM

ok will do

87chevy.com · 10-04-2010, 11:09 PM

Stop Leak stuff for the radiator is a temp fix... if it plugs a hole in the radiator, what does it do to the passage ways? When I get cracked radiators from customer pay jobs, I crack the end caps off and look inside to see the buildup of crap at the bottom.. just saying...
clint

Patsfan34 · 10-10-2010, 10:51 AM

Well I tried a new coolant temp sender and even replaced the fuel filter and still nothing. Truck will not idle, running rough. I am going to pull the plugs and inspect them but a couple people now have said it may have jumped time. Any other ideas you guys might have?

Thanks

MTCK · 10-10-2010, 11:21 AM

I was thinking timing. Unplug the advance control and set your timing to 0d BTDC. Then plug your advance back in and reset the SES lite by unplugging the battery for a minute. Keep us posted.
Posted via Mobile Device

Patsfan34 · 10-13-2010, 09:39 PM

Problem solved. Idle control motor on throttle body is no good (at least thats what I think my friend said). Also the vacuum diaphram right behind that idle control was stuck closed. My friend (the mechanic) troubleshooted for about 5 minutes and figured it out. That's why he's a professional...LOL! Anyway, thanks for all the ideas guys!

10-03-2010, 04:22 PM	#1
Patsfan34 Registered User Join Date: Dec 2008 Location: New England Posts: 661	Engine started running rough 350 TBI I bought an 87 GMC 4x4 2500 about a month ago. Was sitting for a handful of years in a barn at a local farm. I got a great deal on it and knew I could fix most of the stuff it needed. It's said to have 73K original miles. First what i fixed or replace: new exhaust (cat back), new shocks, full tune up (plugs, wires, cap, rotor, air filter), radiator and heater hoses, all 3 belts, coolant flush and new coolant. Radiator had a tiny hole in the center so I bought some stop leak and it immediately stopped leaking. I also changed the power steering pump. i didn't buy a new one cause an engine I had in my garage still had one that I knew worked fine. I was having problems with the starter (it would only catch every other time) so i pulled it out and noticed the teeth were pretty chewed up. I actually had another starter hanging around out of the donor truck for my project so I compared them and they looked the same (different model numbers) but I bolted it in and the truck turned over perfect. I figured it was time to take the truck for a ride to see how it ran. I took it out last Sunday and drive it around for about 30 minutes and it was flawless. This was before I switched the starter and it ran great, sounded great. This Wednesday after I finished with the starter swap I took it for another ride only 5 minutes and when I got home it was running terrible. It will not idle. When I turn it over it starts right up but I have to give it gas to keep it running or it will shut off. Could the starter have caused the problem? I checked everything again hoping maybe a ground came loose but nothing. I pulled the air cleaner off to inspect the TB and I noticed the plugs seem to have melted a bit. Pic below. Obviously I am going to replace them. What could have cause these things to melt? I've had the air cleaner off a handful of times but never noticed the plastic on the plugs melted. When I started the truck today a massive cloud of white exhaust came out of the tailpipe and it was like that for about 30 seconds but then eventually cleared out. Sorry for the long post but I wanted you guys to have all the info. I even pulled the exhaust again just to make sure the cat wasn't clogged and nothing. Any help is appreciated! Thanks, Patsy Attached Images

10-03-2010, 06:43 PM	#2
Patsfan34 Registered User Join Date: Dec 2008 Location: New England Posts: 661	Re: Engine started running rough 350 TBI ^^^

10-04-2010, 07:32 AM	#3
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: Engine started running rough 350 TBI If the coolant temp sender is out, it will tell the computer that intake coolant is -150 degrees or so, so the computer richens up the mix quite a bit. That'll make 'em idle rough, if they'll run at all. Good thing is you can unplug the old one and plug a new one in and just let it rest on the intake manifold to test it. White smoke is generally from water/coolant, but could be from a number of things. Check for bubbles in the radiator when the truck is idling... Last edited by BigBlocksRule; 10-04-2010 at 07:33 AM.

10-04-2010, 09:16 AM	#4
Patsfan34 Registered User Join Date: Dec 2008 Location: New England Posts: 661	Re: Engine started running rough 350 TBI That temp sender is on the drivers side of the engine block right? When I did the tune up I remember disconnecting the wire on that side. I did hook it back up but I will give it a shot. This is the first time I ever seen white smoke come out of this truck. It cleared out after about 30 seconds. Thanks BigBlock. Last edited by Patsfan34; 10-04-2010 at 09:17 AM.

10-04-2010, 09:37 AM	#5
RandyP Getting Old; Going Broke Join Date: Apr 2010 Location: Owasso OK Posts: 2,764	Re: Engine started running rough 350 TBI No, the temp sensor is by the water neck on the intake. __________________ *Why is every used 350 sbc out of a corvette?* There's only two things that excite a man, expensive toys and real expensive toys. *VEGETARIAN: That's an old Indian word meaning "I don't hunt so good."* When the going gets tough, switch to power tools.

10-04-2010, 01:00 PM	#6
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: Engine started running rough 350 TBI ^ what he said, it's right up front. The one in the driver's head is for the gauge or idiot light.

10-04-2010, 10:18 PM	#7
Patsfan34 Registered User Join Date: Dec 2008 Location: New England Posts: 661	Re: Engine started running rough 350 TBI wow good thing I asked! Thanks guys. I will get parts tomorrow and work on it Wednesday.

10-04-2010, 10:21 PM	#8
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: Engine started running rough 350 TBI Unplug the one on the engine and plug it into your replacement without taking anything out of the intake, just leave the new one laying on the intake. If it is the intake coolant temp sensor that's bad, the truck will run better pretty much immediately. If it doesn't help, there's no need to replace it, just hang onto it for a spare for when it does need replacement.

10-04-2010, 10:29 PM	#9
Patsfan34 Registered User Join Date: Dec 2008 Location: New England Posts: 661	Re: Engine started running rough 350 TBI ok will do

10-04-2010, 11:09 PM	#10
87chevy.com BMW & ASE Master Certified Join Date: Feb 2004 Location: Houston, Texas Posts: 1,266	Re: Engine started running rough 350 TBI Stop Leak stuff for the radiator is a temp fix... if it plugs a hole in the radiator, what does it do to the passage ways? When I get cracked radiators from customer pay jobs, I crack the end caps off and look inside to see the buildup of crap at the bottom.. just saying... clint __________________ 1987 Silverado - L83 5.3 w/ 6L80e ,A/C,P/W,P/L,TILT, HID projectors, Wilwood C-10 Pro Spindles w/ 2018 silverado front brakes & C-5 Corvette Rear Disc Brakes 1999 BMW 528i - 5.7 LS1 w/ 4l60e, Ford 8.8 IRS w31 spline posi & FX-r projector retrofit New project: 2006 BMW x5 6cyl AWD to L83 6l80e 4wd to 2WD / RWD A poor man buy's it twice finally got my domain name back, 87chevy.com.... site rework in progress

10-10-2010, 10:51 AM	#11
Patsfan34 Registered User Join Date: Dec 2008 Location: New England Posts: 661	Re: Engine started running rough 350 TBI Well I tried a new coolant temp sender and even replaced the fuel filter and still nothing. Truck will not idle, running rough. I am going to pull the plugs and inspect them but a couple people now have said it may have jumped time. Any other ideas you guys might have? Thanks

10-10-2010, 11:21 AM	#12
MTCK Registered User Join Date: Dec 2009 Location: Fairbanks, AK Posts: 1,830	Re: Engine started running rough 350 TBI I was thinking timing. Unplug the advance control and set your timing to 0d BTDC. Then plug your advance back in and reset the SES lite by unplugging the battery for a minute. Keep us posted. Posted via Mobile Device __________________ -Marcus 1991 V3500 L29 454 4L80E NP205 D60/14 Bolt 4.56's 1984 K30 292 TH400 NP205 D60/14 Bolt 4.56's flat bed 7'6" Meyer Plow 2022 Silverado 3500 L8T Project Daily Driver Project Heavy Hauler Project Plow Truck

10-13-2010, 09:39 PM	#13
Patsfan34 Registered User Join Date: Dec 2008 Location: New England Posts: 661	Re: Engine started running rough 350 TBI Problem solved. Idle control motor on throttle body is no good (at least thats what I think my friend said). Also the vacuum diaphram right behind that idle control was stuck closed. My friend (the mechanic) troubleshooted for about 5 minutes and figured it out. That's why he's a professional...LOL! Anyway, thanks for all the ideas guys!



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