I know this doesn't really belong here, but with all the tbi info i've been getting from here and can't get an answer anywhere else I though I'd ask here. I have an 85 Chevrolet C10 1/2 ton swb truck that I installed a modified TBI fuel injection system on. Here's what I've done so far. It's an 89 350 4bolt block stock pistons rotating assy, stock cam, 85 model 305 heads, Edelbrock Performer 4 barrel intake, tbi to 4 barrel adapter plate, 1 5/8" full length headers, 2 1/2" tru dual exhaust with H pipe and glasspack mufflers, the o2 sensor bung is welded into the driverside header collector, the complete engine wiring harness from the donor vehicle and matching ecm. Now for the problem the engine idles fine, but under acceleration be it moderate or heavy all it want's to do is stumble once you get up to speed you can back off the accelerator and it'll level off and stutter every now and then. So far I've tested my fuel pressure (10psi running), changed plugs, cap, completely disassebled and cleaned the entire throttle body, replaced the fuel pressure regulator diaphram, changed the ecm still no difference. Could someone please help me I'm about to go crazy I need this truck because it's my daily driver now since my other vehicle got trashed.

 

I would check you fuel pressure while driving. You may have a bad pump. You should really have about 12/13 psi at an idle for a stock tbi unit. It should also stay that way under load and Wot. What fuel pump are you using?? Also do you have an adjustable fuel pressure regulator?

 

I'm running the stock intank fuel pump for the G20 van that engine and transmission came from. I have another pump to try if you think that's the problem. I've tried everything else so that maybe it then. And yes I've converted the stock fuel pressure regulator to an adjustable unit using information I found on this site.

 

If you have made your regulator adjustable, then try turining up the fuel pressue until your at 13psi before you change out the pump. Can you tune your own chips??

 

Have you done any tuning with the chip?

 

Definitely need close to 13psi before you go any further on this project. That year C10 was only carb, but the G20 fuel pump would have been for a TBI setup. Those G20 vans had 4.3L Vin Z, 5.0L Vin H or 5.7L Vin K engines.

You transferred all the sensors over to match the ecm? I always hate to "assume" anything so I am going to ask a few other questions just to know exactly what you have.

You stated it's a modified tbi system. Do you know if the injectors are 350 injectors (casting # on top of injector would be 5235206)? What did the TBI come off of?

Your issue definitely sounds like a lack of fuel. It can be a combo of bad pump and too small of an injector depending on where that TBI came from. All of the small block TBI's look very similar if not exactly the same. The only way to know what injector you have is to check casting #'s and make sure they are the same. Once you get your pressure up to 13 then check for injector spray. It is NOT uncommon to have a leaky injector, bad spray, etc especially if the TBI setup sat around more than 30 days with no fuel running thru it.

If the injectors are not performing once the pressure is @13ps you can simply send them off and have them cleaned and flow rated to make sure they are flowing within 1-3% of each other.

 

WOW sorry for the bad grammer guys!! LOL

 

I transfered everything over from the g20 from the in tank fuel pump all the way to the engine and transmission. It's got the stock 350 throttle body and injectors after I changed the ecm both injector are spraying very good now. I also found out today that the map sensor had no vaccum running to it and the plugs are very sooty. I also tested the voltage at the tps and it's running at 1.08 volts at idle so do I have a bad tps or can it be adjusted? I also changed the ignition module and coil which didn't change a thing. Also my tps power wire is supplying over 6 volts at the tps. Is this normal. And no I havn't tried to custom burn a chip or to get a custom chip for lack of funds. This truck was built using parts from 22 different vehicles from my uncles little private junkyard. Heck Ii only have $347 tied up in the whole thing right now. This one's been forced to be my daily driver after my other one got trashed.

 

My tech data source states this about the TPS:

Voltage 0.95 max volts @ idle

The Throttle position Sensor is not adjustable on this engine but should read between 0.36 to 0.95 volts at closed throttle, and about 4.8 volts at wide open throttle.

Here is a link to a thread on here that may help you out. I still think you have a fuel pump/pressure issue.

https://www.thirdgen.org/forums/diy-...ht=tps+voltage

 

Ok that article is a little confusing, do I need to replace the tps sensor? I read the autozone repair guides and they say if the tps reads more than .80volts it needs to be replaced.

 

Is this what your TPS looks like?

 

I'll do you a favor. I have a number of new throttle position sensors in different styles. Let me know what style you have. I also have a couple of used TPS that were good at the time they were taken off the units.

I will send the used ones to you free of charge if you want.

 

it looks like the first one of the post with the two pics, I would really appreciate that.

 

I believe the sensors are both the same, but different angling on the harness. PM me with your address and I will ship the two used ones to you. They've been on my bench for too long now and someone might as well use them.

 

The second picture I believe is an adjustable TPS. It has a screw on the back and i believe it can be adjusted. Not sure.