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.

Dak24

Newbie
Joined
Apr 7, 2021
Messages
14
Reaction score
6
Location
Michigan
Hi all, new to the forum, looking for any info that would be beneficial on these tbi systems.

I have a 93 chevy kodiak with the 366 gasser in it and I'm really having a hard time getting it to run right. I know this site is for the gmt 400s but I was hoping someone on here could just share any information.

The truck starts good, but seems like it runs really poorly to me, and as it warms up it seems like it gets worse. I run it up and down the road a couple times and it can't really even get out of it's own way. it seems like it has a miss that's inconsistent as well.
I've replaced: iac, map sensor, injectors, fuel pressure diaphragm, plugs, wires, cap (haven't been able to get a rotor yet), coil, coolant temp sender on the intake manifold, oxygen sensor.

Tested: fuel pressure 20 psi (my gauge works to 100psi if that matters)
Tps: .55v at idle, 4.44v at wot
Codes: only showed code 12

I had a friend look at it and he messed with the timing when it was running but that didn't help much, I tried spraying around the intake manifold with starting fluid to see if it had a leak but it didn't seem to, I checked the vac lines on the engine when I replaced the sensors and no leaks, I checked the egr and it works like it's supposed to, cold compression is between 135-150.

Any suggestions? I am really confused on this an I've already thrown a lot of parts at it.
 

Dak24

Newbie
Joined
Apr 7, 2021
Messages
14
Reaction score
6
Location
Michigan
Would aftermarket fuel pumps put out to much pressure like that? I see one of the (truck has dual tanks) looks like it's been replaced. I've got a tap still in the fuel line I'll have to see if I can run a ball valve off of that with a return line and see if I can reduce the pressure some
 

gric_az

I'm Awesome
Joined
Sep 29, 2017
Messages
109
Reaction score
70
Location
Sacaton
Vortec pumps are an upgrade to tbi's. Code 12 is related to the distributer. Look that part over, your pickup might be bad
 

PlayingWithTBI

2022 Truck of the Year
Supporting Member
Joined
Jan 3, 2019
Messages
9,552
Reaction score
14,678
Location
Tonopah, AZ
But 20 psi fuel pressure on a tbi is too high. In a regular 350 tbi the pressure is around 12
I have the EP381 pump and I'm running 20 PSI with it but, I have some go fast parts on it. 12PSI is OK, you need to put a scanner on it, look at your fuel trims and O2 cross counts to see if you're not running too rich

Vortec pumps are an upgrade to tbi's. Code 12 is related to the distributer. Look that part over, your pickup might be bad
Code 12 means the ECM is working, that's normal.
 

gric_az

I'm Awesome
Joined
Sep 29, 2017
Messages
109
Reaction score
70
Location
Sacaton
I have the EP381 pump and I'm running 20 PSI with it but, I have some go fast parts on it. 12PSI is OK, you need to put a scanner on it, look at your fuel trims and O2 cross counts to see if you're not running too rich


Code 12 means the ECM is working, that's normal.
That's is correct lol. I was prolly thinking of another. But it wouldn't hurt to take a look at it
 

Erik the Awful

Supporting Member
Supporting Member
Joined
Aug 9, 2019
Messages
7,611
Reaction score
15,528
Location
Choctaw, OK
If you're in an area where you can get away with it, split the exhaust loose between the manifolds and cats and see how it runs.
 

Schurkey

Supporting Member
Supporting Member
Joined
Jan 14, 2018
Messages
10,970
Reaction score
13,755
Location
The Seasonally Frozen Wastelands
1. A fuel pressure gauge that reads to 100 psi may not be especially accurate at 10--20 psi.

2. Install a scan tool, look at the data stream.

3. "Code 12" is "No distributor reference signal", it's telling you the engine isn't running. In other words, perfectly normal for key-on, engine off.
 

Dak24

Newbie
Joined
Apr 7, 2021
Messages
14
Reaction score
6
Location
Michigan
Ok so I did a bit more testing and here is what else I found out:

I set timing to 4 degrees as it recommended for the big blocks ( I unhooked the advance wire, set the timing, then disconnected the battery and connected the advance wire while the battery was unhooked, is that the correct procedure?)

I did a hot compression test and got most cylinders at 145, one of them was at 135

I hooked up a see through spark light tester and seemed to have a consistent spark pulse on all cylinders.

I'm not sure where this puts me, any ideas?

I also forget to mention earlier but this truck has either a bad passenger side exhaust manifold or just a bad gasget on It so it ticks continually.

A couple of you have suggested hooking up a scanner, what type of scanner do I need to do this, all I have is an older actron one, and a phone operated one that uses the torque app. Are there adapter cables for the obd1 systems?
 
Last edited:

Dak24

Newbie
Joined
Apr 7, 2021
Messages
14
Reaction score
6
Location
Michigan
If you're in an area where you can get away with it, split the exhaust loose between the manifolds and cats and see how it runs.

I Don't know if this makes a difference but this truck has no cats. What would happen if I unhooked one of sides of the exhaust, is there something specific I should be looking for?
 
Top