So last year (July) my 91 3.1 started the fire up and die routine. I did all the usual sensor diagnostics. Replaced O2 and IAC. Not the problem but needed replacing. Then off with the plenum etc. and checked the injectors. Resistances all over the place so got a set of reman injectors from RockAuto, put it all together and it's been running like a top since. A few days ago it died driving up to my house. Fire and die. I disconnected the battery and left it for a while. A 1/2 hour later I connected the battery back up and the car started and I drove it home and it seemed fine again until Fri night. Before I dig back down to the injectors is there anything else that causes the same behaviour that is easy to check and rule out first? I really hope none of the injectors have gone bad so soon. I've been reading about the VATS issues. What are the symptoms of bad vats?

 

Is the MIL on when its running? If you cant get it to run you should check codes with a paperclip. If you dont know what it is, take a paperclip, and push each end of the paperclip into the upper right two terminals and watch the MIL flash. It will flash each code 3 times, starting with a 12, then your code and finish up with a 12. If you dont know it, i can give you more details on it, if you do, then see what you come up with.

 

Forgot to add no codes only the 12s.

 

If you replaced the injectors with another set of Multecs, time to change them again.

Otherwise I would attack the ignition control module and the pick up coil.

Note that after disconnecting the battery you should do an idle learn procedure.

RBob.

 

I don't remember the make. May be able to find the invoice. But would they crap out after only 9 months?

 

As RBob said above, start with the ignition parts, wires, coil, pickup coil, module... Check the injectors again, but I don't believe they are at fault... Everyone conveniently forgets the TSB for the 90-92 V6 ignition wiring that can cause many headaches...

 

You mentioned that they were reman's. Which means that they are as old as the ones you replaced. Just that they ohm'd out OK at the time they were selected.

If you can get a decent picture of them and post it. We (posters here) can most likely tell you if they are Multec's or not.

RBob.

 

I ruled out an electrics problem with starting fluid. Sounded great for a couple of seconds then it blew back and singed the hair on my arm! I'll dig out the injectors next. The fuel pressure looks normal, 42 with a slight drop when trying to start. I did read a post that said the pressure could look good but with not enough flow. I would have thought the pressure would drop very low when trying to start if not enough fuel was getting through. ????

 

1. Electrical problems get worse when the wiring gets hot.
2. You should have waited 20 minutes when doing the fuel pressure test to see if the fuel pressure would hold where it was or if there was a pressure loss.
3. If there was a VATS problem, the ECM would hold a code 46... Check for that. Code 46 disables the fuel injection. But it also disables the starter, or should...
4. Fuel injector resistance should be above 11 ohms per GM spec...

 

What's the expected pressure drop v time? I get 42 with the key on and it drops to 32 after an hour. Is that OK?

 

I found the reman injectors were by GB Manufacturing. Any word on how good they are/aren't?

 

GM spec is that the fuel system should hold pressure without losing even 1 PSI of pressure in 20 minutes. Redo the test and check after 20 minutes instead of an hour. However, it sounds like you may need to do something about the injectors.

Did you check for a code 46 yet? Oh, and just because the engine burped on the starting fluid doesn't mean there isn't a problem between the ECM and the ignition module. The ignition module actually runs the ignition until the engine speed has reached 400 RPM, when the EST takes over...

Also, if the ECM isn't seeing a reference pulse signal from the ignition module, the fuel injectors WILL NOT fire...

 

Of course it's not the easy stuff. I got to the injectors and 5 are 12.7 - 12.9 ohms. The number 2 injector is 2.4 so I guess I need a replacement for the replacement. So one bad injector is enough to prevent running?

 

Yes and no. The one bad injector knocks out the other 2 on the same bank, and can harm the ECM. However, I've had my engine running on one bank (like garbage, but it did run) due to a mistake I made repinning my C221 under the dash (injector power connector).

 

The '90 - '92 ECMs ('7730) have one injector driver. So a shorted injectors takes them all out.

The '85 ('86?) - '89 ECMs ('7302) use two injector drivers. Although they are fired together for a batch mode system.


Base91, can replace the one injector but it is only a matter of time until another one goes.

May be worth it to bite the bullet and get a set of rebuilt Bosch injectors from some one such as South Bay or Injectors Plus. And be done with it.

RBob.

 

I knew I was cheaping out with the remans but I figured they'd do better than 9 months and only about 300 miles. I'll go better next time but I still want (need) to replace the original struts/shocks which actually creak as the car moves. Thanks for the info all.

 

I understand. The other side of the coin is that there isn't anything wrong with reman's, as long as they aren't Multecs. The Bosch injectors won't short the coils as the Multecs do.

South Bay has the Bosch reman's for $132 US for the six injectors. Note that South Bay is a TGO sponsor.

The other thing you can do, is if you still have the old injectors is to find one that ohms out OK. Then use it in place of the bad one.

RBob.

 

$132 for the 6??? That's not a typo? That's a really good price for better remans. The one I've got is still under warranty so I can send it back and they'll rebuild it. Again. The old ones were sent in for core charge return. I'm tempted to get one as a spare though!
Thanks.

 

Top of the list:

http://www.southbayfuelinjectors.com...ufactured.html

Even with the Multec being under warranty I wouldn't replace just the one. Sooner or later another one is going to short and leave you stranded.

The problem with Multecs is that the coils short out, as you found out. They can't be rebuilt as rebuilding them is really just cleaning them. And putting new o-rings on and replacing the top filter (basket).

The Bosch injectors are flat out an all around better injector then the Multecs.

RBob.

 

My bad one showed 2.4 ohms. Does that mean it needs a new coil? If so does that mean it can't be rebuilt? I was told to send them the bad one because they didn't have any others to 'rebuild'. Also, the ones shown on the link say 15lbs. I thought the 3.1 used 17lbs? Does it matter?

 

Yes to the coil, and yes to the 'not be rebuilt'. They don't pull the injectors apart such as an engine is when rebuilt. It is a cleaning, spray check, new filter basket, and new o-rings. Usually clean and sometimes paint the exterior.

The actual injector flow rate has been debated for some time now. Apparently these injectors do work in our engines.

RBob.

 

All great info. Thanks.