'93 K3500, 454 TBI, poor drivability

[Idaho83815]

Hello, newby and looking for advice. Thanks in advance.
1993 GMC K3500, 7.4, TBI, 156k miles, 4L80E Auto Trans (Jasper Reman tranny installed 2 years ago)
I have owned it 6 years and it goes to the dump and plows snow in and out of our property in the winter. Always had a high idle (1000-1200) and recently started throwing Code 44 (Lean).
I recently retired so have time and decided to give it some love:
Installed new intake gaskets, New distributor (corrosion and loose ring around the pickup on the shaft of old one), new plug wires, cap, rotor, O2 sensor, gapped the fairly new and clean looking plugs to .035. New frame rail Fuel Filter, Checked vacuum hoses (Steady 16 vacuum at PCV port). EGR Moves freely and seems to hold vacuum.
Code is gone but I have a rough idle till warm, idles at about 800 now instead of 1200.... so that is good.
The main issue now is a stumble/burble/slight backfire out exhaust while steady state driving. Accelerates and pulls well, idles well when warm. Timing is spot on 4 BTC with tan/black stripe wire pulled. Goes to probably 12-ish BTC with wire plugged back in.
I do not have access to fuel pressure gauge or scanner. I have an appointment with a local mechanic in about a week but am trying to do what I can myself, and save money if possible. Thought about other sensors (MAP, Temp, TPS, IAC etc.), but hate throwing money beyond what I already did and felt was worthy.
Also thought about rebuilding TBI as FPR might be suspect, but those kits are spendy these days....
Any words of wisdom?
-David

 

[Schurkey]

Fuel pressure gauge might be available at a local parts store, via their "loaner-tool" program.

Might consider a cylinder leakdown test to verify valve seal.

 

[Amsterdamned96]

I’m far from as knowledgeable as many other long-time members, but have you thought about putting a flathead screwdriver on your injectors to see if they’re opening and closing properly? if you press the handle to your ear and the other end on the injector you should be able to hear it engage and disengage?

 

[Dave11]

It could be a number of things, without a scanner that you could read serial data with you will be pissing in the wind. But if I didn’t have a scanner I would check all the computer ground wires they are known to corrode. Cut and put a new lug on the wire. Other than that I honestly feel like it would be cheaper to take it to a shop. No offense, this happens a lot with me, by the time the car gets to me the customer has done spent all the money they got when they normally could have saved money and time.

 

[Idaho83815]

Fuel pressure gauge might be available at a local parts store, via their "loaner-tool" program.

Might consider a cylinder leakdown test to verify valve seal.

Thanks Schurkey. I will look into loaner programs. I will probably wait on the leak down test, not sure I have a way to do it, but will investigate.

 

[Idaho83815]

It could be a number of things, without a scanner that you could read serial data with you will be pissing in the wind. But if I didn’t have a scanner I would check all the computer ground wires they are known to corrode. Cut and put a new lug on the wire. Other than that I honestly feel like it would be cheaper to take it to a shop. No offense, this happens a lot with me, by the time the car gets to me the customer has done spent all the money they got when they normally could have saved money and time.

Thanks Dave. I hear you on getting it to a shop and will when they have a slot open for me. In the mean time I will look for grounds.

 

[Idaho83815]

I’m far from as knowledgeable as many other long-time members, but have you thought about putting a flathead screwdriver on your injectors to see if they’re opening and closing properly? if you press the handle to your ear and the other end on the injector you should be able to hear it engage and disengage?

Thanks Amsterdamned. I have two nice cones of fuel coming from the injectors, at least at idle or revved up in park..... Will i hear a clicking on and off, what should I listen for?

 

[Sabinoerc]

First thing I would do is to be sure fuel pressure is solid. There’s no feedback on fuel pressure and it can cause all sorts of problems. I went down the route of getting a scanner, looking at traces, etc and at the end of the day it was marginal fuel pressure. I’m not saying that’s necessarily your problem but I wouldn’t start troubleshooting without checking that fuel pressure is good. (And verifying grounds, especially to ECU is good - I think that one is on CTS). Good luck!

 

[Idaho83815]

First thing I would do is to be sure fuel pressure is solid. There’s no feedback on fuel pressure and it can cause all sorts of problems. I went down the route of getting a scanner, looking at traces, etc and at the end of the day it was marginal fuel pressure. I’m not saying that’s necessarily your problem but I wouldn’t start troubleshooting without checking that fuel pressure is good. (And verifying grounds, especially to ECU is good - I think that one is on CTS). Good luck!

Thanks Sabinoerc. I will be working on getting a fuel pressure gauge this week. When you say the ECU ground is on the CTS… you mean the two sets of grounds on the thermostat studs, right? There are four smallish ground wires split 2x2 into ring terminals there.

 

[udidwht]

Thanks Sabinoerc. I will be working on getting a fuel pressure gauge this week. When you say the ECU ground is on the CTS… you mean the two sets of grounds on the thermostat studs, right? There are four smallish ground wires split 2x2 into ring terminals there.

Yes the ground wire is at the T stat housing. It grounds thru the 2 bolts that hold down the T stat housing.