Howdy,

I had posted a week back about an issue I am having in a 1991 Formula with the 5.7 TPI. The car will fire right up if i spray fuel into the plenum however falls because there is no pulse from the injectors, here is a list of things I have both tested and replaced in recent weeks.

Tested.
1. Injectors. I have 12 Ohms resistance at every injector.
2. Injector harness. I have 12 Volts on both plugs with the key 3/4 over.
3. I used a Noid tester (on one injector plug) and have no flashing when cranking.
4. Inspected ground at passenger side rear head to firewall.
5. Injector fuses under the dash and fuse at battery area as well as confirmed that there is 12 volts at the fuse block for injectors.

Replaced.
1. Refurbished ECM.
2. Vats bypass chip from Tuned Port Induction Specialties.
3. Distributor.

I did notice that there is a cut ground wire that is fastened to the metal bracket on the lower part of the steering column. I tried to find where it may have ran to however I can not find another end and assume it was for a previously installed alarm system. There is also another cut ground wire fastened to the inner body panel behind the passenger side kick plate which again may have been for a secondary alarm system that was once in the vehicle. It had both an older Auto Page as well as a Viper alarm system.

Automotive electric and electric in general is outside my wheelhouse so I may be missing something very obvious but from what I have researched the injectors are supposed to ground when the key is turned full over for cranking and my suspicion is that a circuit is not completing somewhere to enable this ground. I have also read that a bad oil pressure sensor may be a culprit but that information seems to be questionable. For what it's worth, the car has good oil pressure when fired and will go above 4 P.S.I while cranking.

If anyone can confirm what those two above mentioned cut grounds may lead to or where my next place to troubleshoot would be I would greatly appreciate it.

 

The oil pressure switch is only for the fuel pump on the mid year cars. It is a parallel path for power, the pump relay would fail and the switch would prevent you from being stranded. Nothing to do with injectors.

If you test all of that it is almost definitely the chip. You could buy one of those VATS bypass modules to eliminate VATS while keeping the VATS chip in the ECM. I think those are like $35-50
Did you try pulling the chip like suggested in the other thread? Pulling the prom but leaving the rest of the memcal will allow the car to start in limp mode.

The injectors are pulsed by a ground signal. VATS prevents the injectors from firing if there isn't a proper signal from the VATS module. And also prevents the starter relay from enabling, but that's not your problem here

module https://www.ebay.com/itm/GM-VATS-or-...EAAOSwXQpeq1fC

 

I didn’t see the mention of you have spark or if the icm has been replaced.
even if the distributor is new could be a icm issue. Have you ohm checked the purple/white wire from icm to d8 of the ecm ? The ground for injector is on the back of the passenger side head.

 

[QUOTE=scooter;6390652]The oil pressure switch is only for the fuel pump on the mid year cars. It is a parallel path for power, the pump relay would fail and the switch would prevent you from being stranded. Nothing to do with injectors.

If you test all of that it is almost definitely the chip. You could buy one of those VATS bypass modules to eliminate VATS while keeping the VATS chip in the ECM. I think those are like $35-50
Did you try pulling the chip like suggested in the other thread? Pulling the prom but leaving the rest of the memcal will allow the car to start in limp mode.

The injectors are pulsed by a ground signal. VATS prevents the injectors from firing if there isn't a proper signal from the VATS module. And also prevents the starter relay from enabling, but that's not your problem here

Scoot, I actually have the module in the car as we speak and no difference.

 

Tuned,

I do have spark as the car will fire if I spray fuel into the Plenum. Regarding the ICM, is that the one in the distributor? If so, I just installed a new distributor yesterday and the one I pulled out appeared to be a reman unit as well so I am tracing someone else's footsteps. Lastly, I am not great with electric so I would not even know where to begin to find D8 on the ecm.

 

You haven't mentioned anything about a bypass module, you said you have a chip burned to remove VATS, there is a big difference between the two.

 

I have the bypass module that splices into the wiring from the cylinder as well as a chip to bypass the Vats. I even checked the resistance in the key and had 8 Ohms, I removed the module and checked the two wires under the column which also had 8 Ohms with the key inserted. I tried using the Vats key with the factory wiring since I had 8 Ohms but have the same result.

 

The resistor is just tricking the VATS module to thinking that there is a key in the lock cylinder, the chip is burned to ignore the signal from the VATS module
A VATS BYPASS module is a little box that emulates the signal the VATS would normally send to the ECM. I linked an eBay auction to one of these modules. This is much different than what you have done here. These modules just hook power, ground and the signal wire to the ECM. If the ICM, that Tuned suggested, isn't the problem and you can't wait for him to burn a new chip or check his work or whatever, then you can try and put in the bypass module

 

I will try checking the ICM and possibly replace it Would a bad ICM cause the ECM not to ground out the injector harness? Also, where would I find this ICM?

 

The ICM is in the distributor, it's that little module screwed to the bottom. If you change it, make sure you use thermal paste or it will burn up.

Not sure why Tuned, and you , said about the head grounding the injectors. The ECM grounds the injectors, the ECM uses the back of the head for it's ground. I think it is unlikely that the ECM can do much of anything if the ground to the back of the head is not good. I would think you would have many more problems and potentially intermittent problems if that ground was bad.

 

That's what I thought but I just replaced the entire distributor last night. Probably didn't have to because the one I pulled out looked fairly new so the previous owner must have been throwing parts at it too.

 

New doesn't really mean anything, especially with the amount of parts coming from China. I have had my share of DOA parts right out of the box.

I still think it's a VATS issue.

Does your fuel pump prime and stay running while cranking?

 

The fuel pump does prime yes, I haven't checked to see if I still get pressure while cranking as most of the time I am working solo however I did run 12v to the jumper by the brake booster to ensure flow.

 

I think that would be a symptom of a bad ICM, the fuel pump won't continue to run while cranking. The ECM only re-fires the pump when it sees signal from the distributor. So if the pump does run while cranking I think that means the ICM is good, but someone else would have to confirm that.