Anyone good with TBI?

[Syndrome]

I've got a 350 TBI out of a 87-91 G20 van in my 1970 GMC. I didn't install the motor, it was rebuilt and put in while the PO owned the truck. Though it was rebuilt he never got it to run correctly so he parked it and it sat for over 2 years.

When I got it I siphoned the tank out, put new gas in it, and siphoned it again. I cranked it over a few times, put a little bit of starting fluid in it and it started up. It idled pretty rough for a bit then settled down and I drove it about 50 feet. I stopped there to bleed the brakes and top off the tranny(it leaks at one of the seals).

I started it up to move it into my driveway and when I put it in gear it would die, at that point my battery died and it was dark so I left it for the next day.

I couldn't get it to start anymore after that. The fuel pump it had sounded terrible, and was rated for 125 psi max, which is much more than TBI needs, so I picked up one of these: Airtex inline electrical fuel pump, 10-14 PSI 35 GPH. I also got a inline fuel pressure gauge and I'm getting about 11.5 PSI, though the gauge is known to read slightly low.

I replaced the gaskets, o-rings, filters, regulator diaphragm, and regulator spring in the TBI.

Its got fuel coming out of the injectors, though it seems a little weaker than other TBI's that I've seen running. Its got spark, with new plugs, wires, distributor, and coolant temp sensor. I swapped the injectors for some that I got from a friend and they spray the same.

I've swapped out the ECM, Electronic Spark Controller, MAP sensor, the module under the distributor. They weren't new parts but stuff I pulled off of another vehicle, same results with any of the various parts installed.

[airdale94]

Have you checked the timing? On the factory setup there's a place to remove or install a jumper (I forget which) then you time it to 0. Then reinstall jumper.

[marvgarr68]

TBI is good if you know how to work on it. Most of the aftermarket fuel injection is TBI. Look online there is tons of info on them they are mostly the same just differant ecu/injectors/distributers/etc. They even have a mod for two throttle bodies one site is tbichips.com the other is dynamicefi.com. I was going to do a dual tbi setup but want something totally differant.

[Bigdav160]

Does it have EGR?

[sean1969c10]

You may want to post this question on the 88-97 board, Chevytech is over there a lot and really knows the TBI systems.

[WIDESIDE72]

I ran a cfi pump out of a 97 vortec truck and an adjustable regulator at the tbi on my 93 gmc. Its my understanding that the tbi runs better with a little more fuel pressure than stock but not as much as the stock cfi pump puts out. I also had a custom chip from brian at tbichips.com. Engine was a rebuilt 97 virtec with a crusader tbi/ vortec marine manifold with egr delete headers comp cam and beehive springs ported tbi from rv morse machine. Ran pretty good considering it was in a heavy k2500 ext cab lwb
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[Syndrome]

Ok I finally got it to run. Apparently my pickup line had some building up in it, even though the tank was clean. And I had to clamp my return line down very tightly(actually never checked to see how much/if any was actually returning).

It runs, but it only idles, and it only idles once its warm. At first it will start then idle up to 1k then drop down to 500ish then die, repeat until motor is warm then it holds idle.

Any time that I touch the throttle then it dies, doesn't matter if its cold or warm, right when I touch the throttle it dies. Does it the same if its in gear or not.

I pulled my TBI and swapped it for one off of my dads Suburban and they both act the same(ruling out idle air controller, throttle position sensor, and regulator). I put in a different MAP sensor that I think works, maybe I should pull the map off of the suburban as well.

I pulled the O2 sensor out and just set it there and it fired it better for the first 2 attempts, then went back to normal. And when I put the O2 back into the exhaust I had to crank slightly longer the first time or two.

[68shortfleet]

I had a 92 suburban with a 7.4 TBI. They share the same basic system design and the same fuel pressure specs as your SBC TBI. Anyways, I once had a very similiar problem as yours except i could get mine off of idle then it would stall out. It turned out to be a plugged up fuel filter that would flow enough and show pressure within to be within spec, but if you tried to drive it it would stall out. I installed my fuel pressure guage and tucked the guage under a windshield wiper so I could see it. It would stall every time when the guage read exactly 11psi. New fuel filter fixed it.

[Syndrome]

Ok, I've got a new fuel filter here I will put in it(even though I just put one it it, I did run it with the dirty pickup line). And I'm showing between 10-12 psi all the time. Not sure how accurate my gauge is though, it costed a whopping $11 for the gauge and the T-fitting.

The idle will go up slightly before it dies, I've even got it above 2k RPM's a few times before it kills. Looking at my TBI while it dies it seems that it still has plenty of fuel when it dies.

[88Ironduke]

Might be a little off base, but since its a TBI system the installer may have wired up a check engine light. Jumper out pins 1 and 2, turn on the key and read the flashes. It should read out code 12 for everything is ok witht he ECM three times and then begin spitting out a code in what ever sequence is required 3 times each and then restarting with code 12 again.

If the CEL is not there you only need to find the ECM, nail down the pin out for the CEL light, wire up a 194 light to a ground source and you now have a chck wallet light. If the dianostic port is not there you have a bit morw work to do. Even though its ODB1 do not count it out. A bad MAP sensor can drive exactly what you're seeing but until you read the codes you're trouble guessing and not trouble shooting. If you check the codes you have narrowed the playing field to old school problem solving and its something the computer cannot monitor. Good luck

88Ironduke

[Syndrome]

This is exactly what I'm going to do this weekend. I got a diagnostic port out of the junkyard yesterday and I'm going to hook it up to my ECM. I will also have to do the check engine light.

This is the wire diagram that I have been using, I hope its correct, so far it seems like it has been.

http://www.ih8mud.com/tech/tbi/wireTBI-1990b.gif

[WIDESIDE72]

Sounds like low fuel pressure to me. Fuel pump?
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[Syndrome]

Originally Posted by WIDESIDE72

Sounds like low fuel pressure to me. Fuel pump?
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brand new fuel pump rated at 9-14 psi, gauge says I'm getting 11.5 ish. The fuel sprays even after the motor stops running. It doesn't appear that the fuel changes much but the motor stops.

[Boog]

The tbi engines have 2 ground wires that bolt down next to the thermostat housing. They must be clean. Some even go so far as to say do not bolt them down together. I've never understood that idea. I forget how many but there are numerous ground wires under the hood. Good idea is to use your schematic and trace them all.
Also you can take the various sensors to the parts store and have them tested before buying new ones. It may even be the ecm that's bad.

[WIDESIDE72]

Originally Posted by Boog

The tbi engines have 2 ground wires that bolt down next to the thermostat housing. They must be clean. Some even go so far as to say do not bolt them down together. I've never understood that idea. I forget how many but there are numerous ground wires under the hood. Good idea is to use your schematic and trace them all.
Also you can take the various sensors to the parts store and have them tested before buying new ones. It may even be the ecm that's bad.

IMO the recommendation not to bolt the grounds together is a redundancy issue. If the connection gets corroded it will lose ground alltogether as opposed to them being separate.

From personal experience, I replaced a tbi pump that was putting out around 10 psi with a vortec pump and and adjustable regulator set at 14 psi and truck ran much better. I only did it because i was not sure how old the pump was and didnt want to get stuck by a failed pump.
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