1991 K1500 Chevy engine issue.

[Hammack1975]

hi guys. I have a 1991 K1500 that was my first pickup that I have been restoring. Half way thru the project it got put off for several years because of a change of employment. I've now started the project again, and run into an issue with my engine. It's a 350 that I built. It is mainly all stock except bore .030 over on the pistons. It has about 10,000 miles on it, and ran fine after the build. I haven't driven it much at all over he past couple years except to crank it and let it idle to keep it running. Now it has a stumble during acceleration. It cranks perfectly and idles fine. If you mash it to the floor it takes off and pulls strong with a slight stumble at around 2500 rpm I'm thinking as I have no tach but it's barely noticeable. Now if you ease off like normal everyday driving it stumbles as if it's running lean when accelerating slowly thru the gears stumbling hard in second and third gears. It will idle all day with no issues. I have replaced entire ignition, plugs, wires, cap and rotor. Checked timing, And fuel is clean and new. I did notice yesterday it threw the service engine light on but it doesn't stay on after switching the truck off. One friend of mine leaned towards possible injector issue, and another said EGR could be culprit. I'm relatively new to working on these TBI units. Just never had much wrong with them so any info or directions to look will be greatly appreciated. Considered purchasing a scanner to see if any codes were thrown but not sure exactly what unit I need to do that yet. Thanks in advance.

 

[BIG_KID]

Jump the A-B terminal on the ALDL to get the codes
The check engine light will flash the codes

 

[Hammack1975]

Jump the A-B terminal on the ALDL to get the codes
The check engine light will flash the codes

Thanks for that info. Just went out and performed that task and the only code showing is 43. After google search I'm assuming that it's a bad knock sensor? Does this sound correct?

 

[magimerlin]

That is the code for it, but..... could be sensor, or wiring. Or could be something else tripping the knock sensor... a bad egr can cause a bad stumble as well.

Sent from my SAMSUNG-SM-G891A using Tapatalk

 

[Hammack1975]

Well after a little more checking this evening I discover the entire wire and plug for the knock sensor is gone. I believe I located the wire, but now have to find a plug to splice in and hopefully that will help. Is there only the one knock sensor on the obd1 early 90's trucks?

 

[skylark]

Just the one above the oil pan rail on the passenger side about halfway back. It goes into the coolant passage.

 

[Hammack1975]

Purchased a new connector today and spliced the wire I believe has to be it. (Only broken wire down there i can find), and still no change. Idles smooth but bogging on acceleration and occaisional backfire. Still throwing a code 43. Not sure what my next step. Perhaps change the knock sensor?

 

[Hammack1975]

I've now replaced both the knock sensor as well as the electronic spark control, and still have the same issue. Under hard acceleration it backfires and acts as is if can't build power. If you were to mash it to the floor then let up on the throttle about half way it clears up and pulls off, just will not build power at wide open throttle. Any help is greatly appreciated...

 

[BIG_KID]

Unhook the battery for a bit and see if the code comes back