help with poor acceleration

[Mr87]

I need some help with my recent problem. I have an 87 GMC sierra with a 350 and just recently it has begun to stumble and stutter when I accelerate rapidly or in the 25-45 MPH range. I can coast relatively fine by accelerating is where the problems start. Also they appear to only happen once my truck is warmed up. I gets very audible knocking sound when it sputters. I've replaced all of my plugs and ensured my wires were all connected and in good shape. One of the associates mentioned it good be my ignition coil but I have no idea where to find this or remove it. I could really use the help and open to all opinions. Thanks

 

[Boone83K10]

could be the distributor or the carburetor if you have one.

Check your timing with a timing light. Should be b/w 10-14 degrees before top dead center. Turn distributor counter clockwise to advance (raise #) or clock wise to retard (lower #). Make sure you plug the vacuum advance going to the carb before timing it.

Check your carburetor with a vacuum gauge. Hook it up to a full manifold vacuum port (PCV) on the carb and plug the other end. Turn your mixture screws all the way to the right and seat them lightly. Turn them back out 1.5 turns to the left. Fire up the truck and take note of the vacuum reading. Turn both your mixture screws .5 turns either way (right is leaning it out, left is richening it) and watch the gauge. You are trying to achieve the highest possible vacuum you can get. Try to keep your idle the same, by turning the idle screw back to the initial RPM that you started at (tach helps) or by ear.

If none of that works then you could be talking about opening up the carb and setting the fuel bowl level, switching power valves, pump cam adjustment or even jetting the carb.

Your knocking tells me that it is starved for fuel when accelerating, so you need to enrichen the mixture.

 

[Mr87]

I have fuel injection actually and yesterday I took the cap off of my distributor and cleaned it out. Wasn't sure if I should try replacing my spark plug wires because after I changed the plugs she ran great no problems for about three days and then it started all over again

 

[Boone83K10]

ok so you have TBI... Yeah put some new wires on then I would check your EGR valve. It could also the TBI plate going bad. I would still check the timing.

 

[89Suburban]

The coil is right in front of the Distributor. Where the center wire from the dist cap goes too. 2 bolts hold it down. Failing coils can sometimes start to act like that. When they heat up and expand the windings inside

Had a few members here with these symptoms trace it down to the ignition switch on the column starting to fail. Also could be the ign module starting to go out. Just a few ideas, trying to track down some better info for ya....

Couple a threads to check out:

http://www.gmsquarebody.com/forum/showthread.php?t=4905&highlight=coil

http://www.gmsquarebody.com/forum/showthread.php?t=4937&highlight=coil

http://www.gmsquarebody.com/forum/showthread.php?t=3420&highlight=coil

 

[Jims86]

I need some help with my recent problem. I have an 87 GMC sierra with a 350 and just recently it has begun to stumble and stutter when I accelerate rapidly or in the 25-45 MPH range. I can coast relatively fine by accelerating is where the problems start. Also they appear to only happen once my truck is warmed up. I gets very audible knocking sound when it sputters. I've replaced all of my plugs and ensured my wires were all connected and in good shape. One of the associates mentioned it good be my ignition coil but I have no idea where to find this or remove it. I could really use the help and open to all opinions. Thanks

When is the last time you replaced the fuel filter?

 

[Mr87]

I just recently changed it not even three weeks ago

 

[Jims86]

I just recently changed it not even three weeks ago

I would check the fuel pressure before anything else...9-13 psi is Factory spec. You may be able to rent the gauge and TBI specific adaptor.
May reveal a bad regulator or failing pump.

 

[MrMarty51]

How many miles is on them sparking plug wires ??? might be better oft to change them just for the peace of mind if nothing else.
Did You, when You had the distributor cap off, scrape that ashy looking deposits oft of them terminals inside the cap ??? that`ll sometimes decrease some of the resistance.
A lot of times, if there is a lot of black soot lookin crap built up on the rotor and the inside top of the dist. cap, it could be a sign of high resistance between the distributor cap and the threads of the sparking plugs, usuall caused from either bad/burned out plugs or sparking plug wires gone to ****.

 

[Mr87]

I haven't changed the wires yet but i know they have at least 6 years of daily driving miles on them im not sure about the PO.I've been looking for suggestions on what people thinks some good wires are. I just got in from changing the ignition coil though which took a lot longer than expected. It was only $26 with a lifetime warranty so i figured why not try it. So I'll post an update tomorrow when I drive her to work and let everyone know if that was the root of the evil.

 

[MrMarty51]

I got some " Omni Spark " sparking plug wires from Oreillys. it says they are OE right down to the core, guess what, they were too. fit as good as if they was right from GM. Made in the USA too.
I was impressed with them.

 

[Mr87]

I changed my ignition coil and the same thing is still happening
My next step is to check my fuel pressure. Can someone point me in the right.direction on how to do this? Thanks

 

[89Suburban]

I changed my ignition coil and the same thing is still happening
My next step is to check my fuel pressure. Can someone point me in the right.direction on how to do this? Thanks

You got to get your hands on a pressure test kit and hook up at the fuel filter or the TBI. They are very expensive. You can try some parts stores to see if they rent them. I know a guy that owns a shot that let me borrow his. There is a write up on here to make one too:

http://www.gmsquarebody.com/forum/showthread.php?t=5838

 

[Mr87]

I think o reillys does the deposit for tool borrowing thing so I'll check that out. Thanks for the link I would really like to try something like that soon. I might also add that if wheel is cut and I'm going forward or reverse at a slow rate of speed ie backing into a spot, my truck will just die out. Could this be related to the overall problem as well or could it be something different entirely. Thanks again for everyone's opinions and help.

 

[Jims86]

I think o reillys does the deposit for tool borrowing thing so I'll check that out. Thanks for the link I would really like to try something like that soon. I might also add that if wheel is cut and I'm going forward or reverse at a slow rate of speed ie backing into a spot, my truck will just die out. Could this be related to the overall problem as well or could it be something different entirely. Thanks again for everyone's opinions and help.

Yup.