Howell Odd Fire V6 Fuel Injection Kit Install

I would take a look at the Idle Air Control Valve. It may be carboned up and not functioning properly. From there you can manually lower the idle speed. If you google "Gm TBI idle adjustment" you will find the instructions to set the idle lower. The fuel pressure may be too high to idle lower.
Adjusting these TBI systems is like working in circles and can make you crazy, but once they are right they run great.

 

This is a great thread for anybody using or planning on using the GM Tbi system. Kyle has done an excellent job of documenting the highs and lows of the getting this system dialed in.
The FIRST thing that you need to check is the RPM signal the ECM is getting, the ECM needs a clean stable RPM signal to properly control fuel to the engine.
the Howell system is getting that signal from the primary side of the ignition system, the tach terminal on an HEI or the negative terminal on an ignition coil. The GM ECM needs a stable 5v square wave RPM signal, the primary signal is not a clean 5v signal especially on the HEI. When using the primary/tach signal it needs to be filtered and converted before it is sent into the ECM, I don't know how Howell is doing this? The output of the crank sensor is a 5v square wave signal.
If you are trying to troubleshoot/tune a GM Tbi system with an unstable RPM input you are just going to be chasing your tail. You are going to need a scan tool or a labscope to check the RPM signal. Once the ECM is reading a good RPM signal you can tune the system. Raising the fuel pressure will cause a richer condition, 15psi is a little high.

 

Just a little update and public service announcement.......
I picked up a strange rattle/tin can popping noise in the right side of the engine compartment. Further investigation led to the discovery of 4 cracks in the battery tray. My battery tray is thin, rusty and definitely needs replacement; but there's too much hunting to be done right now for that project.
I unhooked all wires and removed the battery from the vehicle, placing it on the ground next to the jeep. After cleaning up the cracks with a drill mounted wire wheel I clipped the ground clamp to the battery tray and set to welding them up. I shot a little black paint on the welds once they cooled and reinstalled the battery. Job complete and rattle free with a hand test, I closed the hood, climbed in and fired up the jeep...... Well I tried to fire it up..... crank, crank, crank. Nothing... engine turns over but no start. I noticed that the fuel pump was not priming the system with the key turned on. Fuel pump fuse checked out good so I moved to the ecm power supply fuse. It was blown in spectacular fashion, as did the replacement fuse the second that I plugged it in.
This is a single wire that runs from the battery to the ECM; the only reason the fuse would blow instantly would be the ECM power was going to ground. A quick test light probe showed the power wire had indeed become a ground wire.
Now normally this would be a dead ECM nightmare, but I have a spare ECM strapped on top of the primary unit. A quick swap of two plugs from bottom to top and a fresh fuse in the ECM power supply and the jeep fired right up!
My assumption is that the terminal connector for the ECM power wire was resting on the vertical support tube for the battery tray when I was welding.
In the future I will wrap the electrical connections with a rag to ensure there is no contact.
Over the weekend the jeep had no issues. My wife drove us to different drop off points and then to pickup destinations while Carl and I hiked ridges and draws in search of Mule Deer.
From 500' here at home to 7000' we never opened the hood and the jeep ran perfect. TBI is still my favorite upgrade!

 

If I want to source a used ECM from a wrecking yard, do you know which years and models I should look for? My local yard has lots of older trucks.

 

You need to verify the P/N on your ECM.
Howell uses 3 different models. 87-91 Chevy and GMC is the most common, P/N 1227747
Again, Verify your ECM P/N, you will need to transfer your PROM chip and Cal Pac chip if you ever have to swap your ECM.

 

Thank you. I'll do that. A spare on the trail seems wise.

 

It’s cheap insurance.
These gm systems easily went 100k miles without issue back in the day. That said, a simple trail fix could have left me in a dead ECM situation.