89 k1500 misfire after head gasket

[HeavyChevy443]

Hey so I know there's a ton of posts about this truck having a misfire, but im wondering if my specific situation can narrow down the possibilities, and hopefully save me some money from buying a ton of parts for a truck im just trying to sell.
I blew a head gasket, so I replaced the head as well as the gasket, did a thorough job replacing all the gaskets I could. I also replaced the radiator and flushed the whole coolant system, and made sure I had clean oil in the truck (added oil, ran it, swapped the oil. Repeat). Now I have everything hooked up completely, and I have a weird stumble/misfire. When I idle in park or neutral, it runs fine. When I put it in gear the RPMs drop substantially, and sometimes it shudders like a misfire. My fuel PSI is 10psi while idling in park. The truck is pretty gutless when I drive it and it stumbles on acceleration, but runs at freeway speeds decently. My timing is set to 8deg adv. Oh and I replaced the fuel filter.

I feel like I've narrowed it down to:
Fuel pump
Distributer cap/rotor, wires, and plugs
Maybe vac leak (but I checked thoroughly and couldn't find one)
MAYBE PCV valve???

Can anyone add to or take away from this list?

Thanks!!

[HeavyChevy443]

I forgot to add. The reason I think my problem might be different than others, is because this truck ran tits Mcgee before the head blew. So I would find it hard to believe that the fuel pump or ignition system failed simultaneously.

[Palf70Step]

Is it throwing any codes?

Only thing coming to mind is valve adjustments on the new head.

[sntrym95]

^^ I second the valve adjustment. What procedure did you use? Also, I'll assume you did it but I'll ask anyway - did you label the lifters, pushrods, etc. when you pulled the head and put them back in the right place?

When you set the timing, did you set it with the timing connector disconnected? These engines should be 0 degrees when setting it this way, and you can get away with up to 4 BTDC but that's about it. If it's not chipped, 8 degrees is too much.

[HeavyChevy443]

Yea I definitely matched the correct parts back when I reassembled it. When I adjusted the valves I warned the engine up and did it by sound. Im really not totally sure what other good way there is to do hydraulic lifters. But ya it crossed my mind too.
And Mike im actually not sure what timing connector you're talking about. Im used to older models where they have the vacuum timing advance that you can pull, but im not completely familiar with this ignition system. Could you point me in the right direction and ill definitely give it a whirl!
I've heard of there being a brown wire to disconnect on the firewall by the brake booster but I couldn't find that

[racerop]

I would look at the crank sensor
and the o2 sensors if all the things
mentioned by others are not the
issue

[sntrym95]

Originally Posted by racerop

I would look at the crank sensor
and the o2 sensors if all the things
mentioned by others are not the
issue

TBI doesn't have a crank sensor. The reference signal comes from the distributor.

Originally Posted by HeavyChevy443

I've heard of there being a brown wire to disconnect on the firewall by the brake booster but I couldn't find that

On the 89 it should be on the passenger side of the engine compartment, roughly below the light that comes on when you open the hood. GM moved it inside behind the glove box around 94.

The warm up method is good, but I've always used this method without issue. http://www.centuryperformance.com/va...procedure.html

[HeavyChevy443]

Thanks everyone for your help! As it turned out I found the elusive tan and white wire. It is behind the harness behind the distributor below that plastic cover with the relays. Disconnected it, set the timing to 4deg adv, plugged it back in, and she's good to go!! It's funny cause I've done the timing on this truck a couple times, it was just probably 4 years ago. Thanks again yall!!

Just so other people can maybe pin down their problems, this replicated other problems like poor fuel pressure, clogged injectors, vacuum leak, corroded distributor cap, and im sure a dozen other things.

[sntrym95]

Originally Posted by HeavyChevy443

Thanks everyone for your help! As it turned out I found the elusive tan and white wire. It is behind the harness behind the distributor below that plastic cover with the relays. Disconnected it, set the timing to 4deg adv, plugged it back in, and she's good to go!! It's funny cause I've done the timing on this truck a couple times, it was just probably 4 years ago. Thanks again yall!!

Just so other people can maybe pin down their problems, this replicated other problems like poor fuel pressure, clogged injectors, vacuum leak, corroded distributor cap, and im sure a dozen other things.

Glad to hear you got it working! Enjoy!

[Palf70Step]