4.3 V6 tbi from s10 blazer

I have rebuilt tbi and cleaned it well. new tps sensor, checked all vacumm lines

the injectors won't squirt when trying to start it. They will sometimes and it starts right up. But it only starts once in awhile.

checked grounds and ECM and wires from injector to ECM. Injectors have 12v. So what is telling it not to fire???

I figured out that if I ground the wire from the injector to the ECM the fuel injector will fire (And a whole lot!) It's getting to the point I want to put a switch to ground this out so I can manually prime the engine. Bad idea, right?

It runs fine once started, however every once in a while it will just quick mid trail (mainly on firm impacts)like there's a loose connection somewhere.

could the MAP sensor or IAC cause this??

Anybody??

Pdaddy got any ideas?

Nobody??

Do I short it out with a switch or replace every damn sensor in the truck!!!

Oh yeah, the diagnostic port thing don't respond either. Tried scan tool and diagnostic reader. :confused:

So please tell me someone knows what's going on?

I think your ECM is fried, or possibly just the calibration chip. I imagine it's a 1227747 ECM so they are very easy to find at salvage yards and stuff. Very few things would prevent the injectors from firing at all:

- Bad ECM/chip
- Bad ignition system (i.e. no tach signal)
- Bad wires to the injectors or distributor

ECM+no sensors+working distributor=fire injectors, period. It would be in limp home mode but those injectors would fire. It sounds to me like you've got a bad ECM or a bad wire. Does the diagnostic port *ever* work?

Andy

the service engine light works, but when you jumper it with key on it doesn't work. when the engine is running and you jumper wire it, it bilinks real fast.

The diagnostic tool just says vehicle not responding.

I took the ECM out and apart, I didn't see any blown up stuff or burnt things.

The wires are great to the injectors checked them with an ohm meter and traced them.

I did see a round filter on a vacumm type module. It's connect to a vacumm hose from the MAP sensor which is plugged into the TPS. Well this filter is really dirty and I removed it to see if it starts, no change. However when it is running and I install the filter the engine sputters and tries to die.

Is the ECM grounded by it's mounting bolts?? cause right now it is sitting on the floor, and otherwise it is installed in a ammo box, not bolted down just wrapped with bubble wrap.

What do you mean ECM+no sensor+working distributor = fire injectors

what do you mean no sensor, I still haven't replaced the MAP or IAC (but cleaned)

Also what does the distributor have to do with the injectors, does it tell computer when to pulse injectors so they're insync or something??

As you can tell electrical stuff ain't my bag baby!

I guess I have to ask, does this still use the factory intank pump? if so the sharp jolts you say it is taking and dropping out on could be coming from the fuel pump & mount. its very loosly mounted and can be dislodged, if so it will act like an Injection problem. you will of corse have to drop the tank and remove the sending unit, I have seen where they are hanging from the fuel hose. very bad design. if you can use a hose clamp or Zip ties to hold it to the support tube that goes down into the tank if you find this problem. and double check the ground wire on the inside of the sender its self. happy hunting.

It is always get fuel to the line.

You're right the pump is a bad design. It fell of about 2 trips ago and a new pump installed major PITA. That was hard to figure out also cause you could still hear it running in there but it was just sending fuel around the tank

For the future if you need to change on of these pumps I suggest cutting an access hole in floor, much easier!

Thanks for the reply though, it seems this may continue to haunt me though?

bad oil pressure switch? You can swap to an inline E2000 fuel pump to avoid the intake drama.

Would the oil pressure switch prevent it from starting?

if the injectors are getting 12 v but its not shooting fuel check for spark. If it is getting spark then there is a wiring problem with the injectors to the ecm. if it is not getting spark then the problem is somewhere between the distributor and the ecm. could be the icm, could be wiring, could be the pickup in the distributor.

oil pressure switch will not keep it from starting, all it does is power a oil light on the dash.

On a lot of GM fuel injection systems (TBI and TPI) there is always 12 volts to the injectors and the ECM sends out ground to fire them. I would start with the distributor. Make sure all the connections are tight. You may want to replace the ignition module (cheap!), welding on a truck will kill these quick. The ECM cannot fire the injectors without sensing the distributor turning and ready to fire. You mentioned the scan tool not reading the ECM. Is it a good scanner and a good connection? If so, your ECM may be bad. Like someone said, they are popular and cheap. You might want to borrow one from someone else if you can. I once used a 2.8 ECM to run my 454TBI. It ran, just not well. I now use it for a trail spare.

if the injectors are getting 12 v but its not shooting fuel check for spark. If it is getting spark then there is a wiring problem with the injectors to the ecm. if it is not getting spark then the problem is somewhere between the distributor and the ecm. could be the icm, could be wiring, could be the pickup in the distributor.

oil pressure switch will not keep it from starting, all it does is power a oil light on the dash.

GM uses a oil presure switch in parellel with the fuel pump relay to allow the truck to start and run if the relay fails. If your TBI engine takes a lot of cranking to start, the relay is probably bad. The guage and/or light has a seperate sender.

Is the ECM grounded by it's mounting bolts?? cause right now it is sitting on the floor, and otherwise it is installed in a ammo box, not bolted down just wrapped with bubble wrap.

The ECM is grounded through the wiring harness. On the intake manifold on the passenger side beside the distributor is a big ground junction. You might want to check and make sure it is clean and all the wires are connected. BTW, sounds like you have fuel pressure if you grounded an injector and fuel sprayed.

GM uses a oil presure switch in parellel with the fuel pump relay to allow the truck to start and run if the relay fails. If your TBI engine takes a lot of cranking to start, the relay is probably bad. The guage and/or light has a seperate sender.

I've done 4 TBI installs and none of the harnesses were wired that way

I will tell you flat out the oil sender in no way interferes with starting or running on these vehicles. the last GM to have this function was the 140 aluminum blocks in the vega's & Astor's. I have change countless oil senders for leakage and not getting a signal to the dash.

I would start with the following... FUEL? got any?.. electricity? got any? there is a tool you can buy or you can check for voltage at the TBI plug to see if it getting a signal(do you have a test light?)use it!. does the engine run when it fells like it? after countless attemps? Timing chain jumped?, does it sound wierd hooting nosies when cranking? and then sound like its firing into the exaust or out the intake? has anyone had the engine out for any reason? there is a main ground on the back of the right hand head right above the bell housing, has it been removed? rusted off? CHECK IT!
Good luck and happy fixing!