TBI conversion almost done, truck is running

[mouse]

After taking most of the past month to swap a TBI system from the '89 suburban I bought onto my '77 blazer, tonight was the first time it has fired back to life. I can't wait to get it on the road.

It has an issue starting though. Even with the 2-second prime from the computer, the TBI is not giving enough gas to start everytime. After sitting, I have to pour a teaspoon or so in the TBI for it to fire. I guess the fuel regulator /diaphram needs to be replaced. The engine surges slightly at idle. My guess is that it is fuel related as well.

I did not rebuild the TBI unit before installing, and have checked for vacuum leaks with a propane bottle, but couldn't find any. Any recommendations?

I will post pics when its on the road (and has a front axle installed!)

 

[Thunder]

What about the Coolant temp sensor Did you swap /hook one up?
TBI wont run right without one.

 

[mouse]

Yes new coolant sensor, among rebuilt dizzy, new cap, wires, water pump, fuel tank, fuel filter (line and in tank), all fuel o-rings, knock sensor, O2 sensor.

After some reading on Third Gen, sounds like it could be an injector problem. I did notice that the drivers side was "dripping" while running, rather than a good spray pattern. Might be time for an injector change...

 

[Russ]

I had a similar problem a while back. Truck would not start without pouring a little fuel in the throttle body and the injectors were dripping when running. I put a scanner on it and the brand new GM MAP sensor I put on the engine was reading at the upper limits. I put an old MAP sensor that I had back on and everything worked fine after that.

Russ

 

[mouse]

Thanks for the info, I'll give it a shot.

Swapped in two different MAPs - no change. The TBI is simply staying dry while cranking...time to move on to rebuild the regulator...

 

[mouse]

Changed the fuel pressure regulator and rebuilt the TBI tonight...no change. The injectors have a nice cone-shaped spray pattern, but while cranking, they don't give any gas. Looks like I'll be buying a new fuel pump tomorrow.

I really hate dropping gas tanks !!!!

 

[dyeager535]

You've checked to make sure the injectors are even getting a pulse when it won't run? (noid light)

 

[mouse]

I've got a reman dizzy, and getting good spark while cranking. I did not check for injector pulse (no light), but since it runs great once started, I don't see how that could be an issue. I have not seen anything in my manuals about a different start routine.

 

[dyeager535]

Lack of enough voltage on the injector feeds while cranking will not allow the injectors to fire. Ask how I know.

If you are getting pulses while it's cranking, your ignition is fine in all regards. You've obviously proven it's not ignition if you know both that you've got spark and injector pulse.

If it *runs* fine after you give it a help with fuel, starting, how is it fuel related?

You said in your latest update that it runs fine once you get it started, does that mean the surge you mentioned earlier is gone?

I'm not stating that it definitely IS an ignition issue, but testing that is a heck of a lot easier and cheaper than replacing a fuel pump as a diagnostic test.

Make your own light out of a 194 bulb and a piece of wire soldered/taped/wrapped around each strand of the wire that is on the outside of the bulb. Disconnect the injector plug, stick each bulb wire bare end into the injector plug, lay it up on the cowl, (most tools you buy don't have enough length to do this) get in the truck and crank it, make sure it's got a pulse. If like me you've got plenty of old bulbs laying around and a length of thin wire, this will cost you nothing.

 

[mouse]

Lack of enough voltage on the injector feeds while cranking will not allow the injectors to fire. Ask how I know.

If you are getting pulses while it's cranking, your ignition is fine in all regards. You've obviously proven it's not ignition if you know both that you've got spark and injector pulse.

If it *runs* fine after you give it a help with fuel, starting, how is it fuel related?

You said in your latest update that it runs fine once you get it started, does that mean the surge you mentioned earlier is gone?

I'm not stating that it definitely IS an ignition issue, but testing that is a heck of a lot easier and cheaper than replacing a fuel pump as a diagnostic test.

Make your own light out of a 194 bulb and a piece of wire soldered/taped/wrapped around each strand of the wire that is on the outside of the bulb. Disconnect the injector plug, stick each bulb wire bare end into the injector plug, lay it up on the cowl, (most tools you buy don't have enough length to do this) get in the truck and crank it, make sure it's got a pulse. If like me you've got plenty of old bulbs laying around and a length of thin wire, this will cost you nothing.

OK, I'll give it a shot. Gotta figure this out before I go crazy.

 

[mouse]

Dorian,
I did another check of the circuit to the injectors today. I build a "noid" light with a dash light 168 bulb to test the circuit. Under cranking conditions there was no power. I thought the circuit was powered in "start" but apparently not. A quick switch to the relay power (the painless add-on fuse block uses a boach relay to switch the "ignition on" circuits on) and the injectors started working during start.

I changed the fuel pump and repaired the float resistor while I was in there so the gas gage would work properly. I have the '77 tach gage cluster - small fuel gage, and amazingly enough the '89 sender works with the old gage.

Thanks for the help. I owe you a beer.

Once the new front axle is in, I'll work out any bugs left in the TBI (poor idle).

 

[dyeager535]

Glad to hear it was that "simple" and you are up and running, if a bit poorly at idle.

Have you done the IAC adjustment procedure over at thirdgen.org? You say you've checked for vacuum leaks, if you are sure that isn't a factor, IAC setting is another one that you can't go wrong with.

 

[mouse]

I'll read up on it.