1988 C1500 tbi help

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

open_road_toad

OBS Enthusiast
Joined
Mar 25, 2022
Messages
65
Reaction score
49
Location
Wooster, Ohio
Hey Everyone, I’m posting this in hopes that one of you had the same issue and can give me some guidance. I was up til 3am working on my truck last night and she’s not running any better. Here’s the situation as of this morning:

A couple of months ago I rebuilt the TBI. I installed AC Delco injectors and did a full gasket/seal kit. I replaced the fuel pump and spark plugs. I also installed a throttle body spacer as the interwebs says that improves throttle response.

Truck ran great for a couple of weeks then started running rough. It has a rough idle but not all the time. It acts as though it’s missing or sounds like it has a big cam in it. It drives really bad at part throttle. It has stalled on me a couple of times.

Yesterday I replaced the following:
Intake gaskets. EGR valve, 02 sensor (single wire drivers side right at the back of the manifold) distributor and coil (summit racing). I also replaced the throttle cable. I replaced all the vacuum lines and inspected everything. I did not see anything bad when I had the intake off.

Truck fired right up. I set the timing after letting it warm up (disconnect the wire before). I’ve done the IAC reset and you can hear it actuating. When I rebuilt the throttle body I cleaned it well and it seems fine. After I set the timing I wrapped the throttle a few times and it sounded good. As soon as I put it in drive it started acting up again and stalled. At that point I shut it off, got a shower and went ti bed.

I’m having a coffee now and am going back out to the truck. What am I missing? At this point I’m ready to take it to a shop because A. I’m at a loss and B I don’t have diagnostic tools.

I have a new Delphi fuel pump that I plan on installing in a couple of weeks. This truck is my daily driver and she’s a good truck.

Thanks in advance.
Todd
 

Harry Dawg

Newbie
Joined
Feb 13, 2023
Messages
21
Reaction score
40
Location
Georgia
Have you tested fuel pressure? It could be a restricted line, as it sounds like you have checked all of the other boxes related to the fuel management system.

Another thought is this might be an ignition issue v.s. a fuel issue, as they often display the same symptoms.
 

sntrym

I'm Awesome
Joined
Sep 9, 2015
Messages
249
Reaction score
135
Just from your description it sounds like it's running lean. It could also be a misfire as Harry Dawg suggested.

Can you verify the injectors are the correct ones for that engine? If you still have the old ones, try putting them back in and see if that makes a difference. You can also pull the air cleaner and check to make sure both are firing and the wiring to them did not get pinched or cut.
 

open_road_toad

OBS Enthusiast
Joined
Mar 25, 2022
Messages
65
Reaction score
49
Location
Wooster, Ohio
Thanks for the replies.

After breakfast I went out to the truck a defeated man. I popped the hood and proceeded to spray the engine bay down to clean off the engine degreaser from the night before. While spraying down the engine on the passenger side I noticed a exposed terminal on the distributor cap! One of the wires had come off last night while I was wrangling with the cap trying to get at the oil pressure sending unit that’s at the back of the block under the distributor.

I plugged the wire in and fired the truck up. She runs great!

I was so happy that I drove the truck around for a hour. Running better than ever.

Next item on my list is new exhaust system. The factory cast manifolds are shot and I’ve got multiples exhaust leaks. I am going full stainless steel headers and Y pipe from Summit.

Here’s a couple of pics of the finished product from last night.
 

Attachments

  • D491B9B4-C7FF-4E5F-8E3C-65F4C12794B0.jpeg
    D491B9B4-C7FF-4E5F-8E3C-65F4C12794B0.jpeg
    311.9 KB · Views: 27
  • 977259B1-3D8F-4EF9-A75D-438A474387EC.jpeg
    977259B1-3D8F-4EF9-A75D-438A474387EC.jpeg
    428.5 KB · Views: 27
  • FAFA1052-7CEF-4D89-876E-C9341F5EB0D4.jpeg
    FAFA1052-7CEF-4D89-876E-C9341F5EB0D4.jpeg
    283.5 KB · Views: 28

GrimsterGMC

Supporting Member
Supporting Member
Joined
Nov 3, 2021
Messages
1,344
Reaction score
4,475
Location
New Zealand
Thanks for the replies.

After breakfast I went out to the truck a defeated man. I popped the hood and proceeded to spray the engine bay down to clean off the engine degreaser from the night before. While spraying down the engine on the passenger side I noticed a exposed terminal on the distributor cap! One of the wires had come off last night while I was wrangling with the cap trying to get at the oil pressure sending unit that’s at the back of the block under the distributor.

I plugged the wire in and fired the truck up. She runs great!

I was so happy that I drove the truck around for a hour. Running better than ever.

Next item on my list is new exhaust system. The factory cast manifolds are shot and I’ve got multiples exhaust leaks. I am going full stainless steel headers and Y pipe from Summit.

Here’s a couple of pics of the finished product from last night.
So many times we think the problem was something we were just working on when it was actually something we were working around and knocked off. I've got to the point where I will only do one fix at a time and fire it up and run it to make sure all is good, that way it is easier to determine what went wrong if it does.
 

PlayingWithTBI

2022 Truck of the Year
Supporting Member
Joined
Jan 3, 2019
Messages
9,856
Reaction score
15,499
Location
Tonopah, AZ
I've got to the point where I will only do one fix at a time and fire it up and run it to make sure all is good, that way it is easier to determine what went wrong if it does.
Meh, what's the fun in that? Roll the dice and throw everything on you can think of. Don't use a scanner, or any other diagnostic tools, and see how long it takes to make it happy. :Big Laugh: :rofl:
JK!

OP - glad you found it :waytogo:
 

GrimsterGMC

Supporting Member
Supporting Member
Joined
Nov 3, 2021
Messages
1,344
Reaction score
4,475
Location
New Zealand
Meh, what's the fun in that? Roll the dice and throw everything on you can think of. Don't use a scanner, or any other diagnostic tools, and see how long it takes to make it happy. :Big Laugh: :rofl:
JK!

OP - glad you found it :waytogo:
Ah, you are referring to my younger days. When 6 mates, each with a beer in hand, would stand around the front of the car with the bonnet, up all offering a different opinion as to why it won't run properly. Visualizing "King of the Hill". After about 2 hours of debate and a couple or more beers each and we all dive in doing whatever we thought it needed. In the end it would start up but nobody knew who it was that actually fixed the problem, but that didn't matter as we all piled in and headed into town to Hoon around until the cops sent us home for our own good. Yep, the good times...
 
Top