87 GMC Pickup Sputtering. Cant Fix

[Viperdude152]

Hey guys

We brought the truck to our mechanic 3 times and he cant find the problem. The whole ignition is new. Plugs, wires, cap, rotor, coil. I guess he put in a newer style of cap and rotor with the coil outside of the cap instead of ontop.

well anyways it sputters like crazy. Well. I shoudl say stumbles..? Basically it feels like from time to time its not running on all 8 cylinders. HUGE power drop and we tow our horse trailer with it. It just happend recently about 4 months ago. The engine will run strong when its cold. But once it warms up it starts stumbling. Almost for the whole day it will run like crap. Now and then it will run great. almost like someone fliped on a switch and then it runs good. Then this switch gets flipped off and the engine runs like crap.

Anyone have this problem before? Its not the fuel pump or fuel filter I have had fuel problems in the past and this deffinatly isnt a fuel problem. Unless im wrong. The truck it throttle body Fuel Injected. Im guessing these have a MAP sensor?

thanks guys. Hope to hear from you!

Justin

[bigarmzz]

try the map sensor, and the throttle position sensor.....(about $30 each at advance auto)....there both located side by side, on the left side of the throttle body, and only take 5 minutes each to change

believe it or not, a bad O2 sensor can do this as well

is your check engine light on?

Originally Posted by Viperdude152

Hey guys

We brought the truck to our mechanic 3 times and he cant find the problem. The whole ignition is new. Plugs, wires, cap, rotor, coil. I guess he put in a newer style of cap and rotor with the coil outside of the cap instead of ontop.

well anyways it sputters like crazy. Well. I shoudl say stumbles..? Basically it feels like from time to time its not running on all 8 cylinders. HUGE power drop and we tow our horse trailer with it. It just happend recently about 4 months ago. The engine will run strong when its cold. But once it warms up it starts stumbling. Almost for the whole day it will run like crap. Now and then it will run great. almost like someone fliped on a switch and then it runs good. Then this switch gets flipped off and the engine runs like crap.

Anyone have this problem before? Its not the fuel pump or fuel filter I have had fuel problems in the past and this deffinatly isnt a fuel problem. Unless im wrong. The truck it throttle body Fuel Injected. Im guessing these have a MAP sensor?

thanks guys. Hope to hear from you!

Justin

[60-66 Nut]

Justin, you might also try unhooking the EGR valve to rule that out.

60-66 Nut

[CLASSIC87']

From my personal experience I will tell you that it is the distributor assy. It seems that the lower bearing on the shaft wears out and it makes it off balance and wobbles. In turn it misses on the contact points on the distributor cap. I had a 92' p/u w 80k miles, a 95' Tahoe w 75K miles, and another 95' Tahoe with 90K miles. ALL of these vehicles I had the same "missing" problem (ALL 350 F.I.)..... I had the distributor replaced, and the problem went away. It is a very irritating problem, you may call a local GMC shop and they may tell you the samething. Good luck.....

[CLASSIC87']

BTW: mine ran EXCELLENT when the Engines were COLD.... and as soon as they warmed up they went to crap as well.

[Viperdude152]

Hey thanks alot guys. I will check all those out. I have been going nuts trying to figure it out. To bad its not a rotary 13B engine. I know them. lol.

How much good is it to throw in a MSD HEI distributer? will it help power at all? or is it basically a waste without other upgrades?

Justin

[87 STEPPER]

When you do the distributor id'e check all the rubber fittings that hook up to the map, egr, and throttle body they become dry rotted and sometimes this occurs on the lower side of them and from a glance they may look good but can be junk and if there sucking air you will have a rough running engine.

Good luck

[bigarmzz]

i just had a friend come over today with his 87....same problem....i went over and over what i thought it could be....

ended up being the idle control valve...($27 at advance)...probably saved him $100 worth of diagnostic fees