Missing On Acceleration
 

Truck is a 1990 gmc K1500 with 5.7 crate engine.

On rapid acceleration it would stumble and lay flat then throw a 43 error code.

I replaced the knock sensor and the pigtail which were both about 1 year old.

I then replaced the electronic spark control module and the $45 plastic connector on it.

I am no longer throwing the 43 code but still have the motor laying down on rapid acceleration.Sometimes it will run flawlessly but most of the time it accelerates in spits and spurts then it takes off.

I put a new cap and rotor on it which did nothing and after work today I'll put in new plugs and new wires but I am at wits end on this thing.

Any ideas if the plugs and wires don't work?

Re: Missing On Acceleration
 

Does it have EGR?

Do you have a fuel pressure gauge?

Re: Missing On Acceleration
 

It has an egr valve and if you push on it it boggs down at idle.
I have a pressure gauge and get 13 pounds of pressure and the lowest readng was 12.5 pounds at wide open throttle going up a on ramp which quickly jumped back to 13 pounds.
It has a new fuel pressure regulator in the tbi and new fuel pump in the tank.
I am waiting for it to cool down right now so I can change the plugs and wires.

Re: Missing On Acceleration
 

Have you checked timing? Should be set to 0 top dead center with brown wire under brake booster unplugged.

Re: Missing On Acceleration
 

Timing is at zero and on this truck the wire is on the passenger side.I did manage to put 4 new plugs in it so far and 4 new wires on the drivers side.I went with 8.5 mm msd wires and they needed to be cut to length and one end put on them.
My coil is a factory part and the tower on it had some oxidation so after dinner I will go to the parts store and order up a new one.
The 4 wires pulled so far looked good as did the coil wire and the plugs.I will ohm them out to see if they were broke internally.
I am saving the passenger side for the morning but will put the last 4 wires together tonight.

Re: Missing On Acceleration
 

Does it have old gas? I say this because you mentioned it only sputters on acceleration, my truck does this after sitting for over 3 months with old gas, after I fill it up sputtering goes away after about 2 miles down the highway.

Re: Missing On Acceleration
 

It has new gas.
If you can remember what a burnt sparkplug wire on a header or bad points feel like it is similar.
It is way down on power but as the rpm comes up it feels like more cylinders are getting power.I thought it was scattering spark in the cap but that wasn't it and the distributor feels very tight as well.

Re: Missing On Acceleration
 

Pull the vacuum hose off the EGR and plug it with a golf tee and take it for a ride.

Re: Missing On Acceleration
 

When I swapped in a 350 from a 305 years ago I also installed a Hypertech chip in the computer under the glove box. I also tried an Accel dist. module and on a test drive my truck behaved exactly as you're describing. I took the Accel module out and went back to the stock module and it's worked great ever since. One thing that is helpful is to have a dial-back-to-zero timing light. You can verify your total timing at 2500~3000 rpms. It's good info to know when you get in a tuning situation like this.

Re: Missing On Acceleration
 

It was two bad plug wires.
The passenger side exhaust manifold has been replaced a couple of times now and the heat shield was making contact with the wires making them extremely brittle.
I pounded the seam on the shield flat so it will clear the thicker wires.
Truck has run good for two days now.