'90 Firebird 3.1L - Won't Start, I'm Stumped!

I’ve had this car far longer than I like to admit. Indeed, it was my first car. She’s now up to 106k orig mi, and just died on me. Drove it from MS to NC to CA, and it died a week later. It has me stumped.

It failed smog with high CO at 2500rpm. The same day, it started running very rough, then lost all power, then died over the course of a day.

First shop:

  • Limped into the parking lot.
  • Tune up overdue. Replaced plugs, wires, cap, rotor, air filter, fuel filter. $$. No change.
  • Hole in radiator. Replaced. $$$. No change.
  • Plugged O2 sensor. Replaced. $. No change.
  • Swapped ECM. No change. Swapped back.
  • Towed 25 miles to nearest diagnostic shop. $$

Second shop:

  • Flat rate diagnostics (6.5 hrs labor, wow)
  • Result: Internal alternator short, high resistance in 5 of 6 injectors.
  • Towed 25 miles home.


  • Swapped alternator. No change. $
  • Fuel pump relay swapped, sounds normal. No change. Swapped back.
  • Fuel pump pulled, strainer checked. All good.
  • Fuel pressure at rail normal (39 psi key on acc, 45 psi cranking).
  • IAC cleaned. No change.
  • Spark tested visually. Looks good.
  • Battery tested bad. Replaced. $$. No change.
  • Checked and cleaned all grounds, electrical connectors, harnesses, etc.
  • Checked all vacuum lines. Looks good. No fuel smell.

No idea what to do now. Any ideas for things to check or test?

Here’s one hint… if I spray WD-40 into the intake, I can get it to idle PERFECTLY for 5-10 seconds before it dies.

I guess I’d start with a compression test. WD-40 might temporarily be sealing leak (head gasket, cylinder rings, whatever) until it burns off.

If it runs with a shot of WD40 that points to a lack of fuel delivery. If the fuel pressure is correct at the rail then you need to move downstream to evaluate power supply to the injectors.

Instead of spraying WD40 down the throttle, spray it around the intake manifold gasket and try again. If that works, then look at replacing that gasket.

Did anyone do a compression check?

Sounds like you have an injector problem as the second shop stated. I have seen these GM cars shut down all of the injector due to one injector having low resistance (shorted). Check the injectors again and leave the shorted injector disconnected, it should start.

I don’t recall ever being told a compression test was performed, nor can I find it on any shop paperwork.

keith - It took some research, but I understand what you meant now about spraying it around the intake manifold gasket. I will try that when I get home. I had been told about a year ago that I should consider replacing them someday, but I don’t recall the reason why a mechanic mentioned it.

cigroller - How would I evaluate power supply to the injectors? I do have a multimeter accessible.

joedcorn - I’ll run a cold compression test when I get off work this morning.

Nevada_545 - What is the procedure for testing the resistance of this injector? Must it necessarily be removed?

A simple way to do a quick check of the injectors is to just use something that will make like a stethoscope one them while someone else cranks the engine. I often just use a length of vacuum hose as a makeshift stethoscope. “Noid” lightsare available at auto parts stores and serve as a quick check on power supply.

The check the resistance you just unplug the injectors and use your meter on the ohms setting - just connect the leads to the injector plug. What you’ll need to know is what their resistance is supposed to be.

Your best friend right now would actually be a GM repair manual.

From ohm readings I have taken in the past of injectors you should see around 15 ohms for a normal resistance reading. Comparing readings of all of the injectors should help also establish a good resistance number. They all should be close to the same reading. I would suspect any that show more than a 2 ohm difference.

From what I have read here it sounds to me that the injectors may not be getting power to them. Usually they are tied to power through a fused circuit and the return side of the injector circuit is controlled through the PCM. Have you checked to see if the injectors are getting voltage to them while the ignition is turned on?

Check fuse #2-10 AMP/Fuel Injector Power 1 and fuse #6-10 AMP/Fuel Injector Power 2


Checked both fuses yesterday and they looked perfect.

Compression test showed 170-175 psi in all cylinders, cold. It won’t run for more than a few seconds, so a warm reading just isn’t possible.

Plugs all looked good, if not a little oily. I expected as much, with a much cranking as I’ve done and as little running as it has done.

Have a Chilton repair manual at my disposal. I don’t really understand the whole injector stethoscope comment, cigroller. I found an injector light set, but I’m not sure how it works.

Heading outside with my meter right now!

Looks like I forgot to hit Post before I went outside. lol

Can only access 1 or 2 of the injector harnesses without dis-assembly. However, that gave me access to see if they’re getting juice.

Injector - “14” to 15" @ 2000 ohms scale
Harness - “.27” @ 10 DCA scale, “.85” @ 20 DCV scale (while cranking)

Looking into difficulty of removing the upper plenum.

Still unable to get to the injector harnesses. I’m amazed as to how the previous mechanic was able to without removing the plenum.

I found his original documentation. It’s not what I was hoping to find…

Spec Min: 11.8 ohm, Spec Max: 12.6 ohm
Injector 1: 11.17 ohm
Injector 2: 9.97 ohm
Injector 3: 7.43 ohm
Injector 4: 12.07 ohm
Injector 5: 12.90 ohm
Injector 6: 11.90 ohm

My measurement was taken on Injector 5, IIRC.

Need to decide if I want to continue at this point, or part the vehicle out.

I don’t understand what you just said.

It seems that you said that the injector specs are supposed to be 11.8-12.6 (which is a pretty narrow range), but that you have injectors 2 & 3 below spec. Except then you said you measured at injector 5? If so, how to know what the other measurements are?

It looks to me like you have two bad injectors. But I can’t tell what you’re reporting.

I’m going back to the original story and wondering what could have happened on a cross-country drive to cause multiple injectors to fail.

I’m not sure that 2 bad injectors after 22 years is anything weird enough to obsess over, though obviously something else could be a root cause (presumably electrical).

I would also say that all 6 injectors probably came off the same production line at the same time & have been subject to the same conditions. So I wouldn’t be shocked if other injectors would follow. If it were me and I wanted to keep the car & everything else was in fairly good condition then I’d probably just replace them all.

I can’t believe a couple of injectors out of spec would cause the car not to start. For all we know, they might be working fine. When you are trying to start the car you have the intake plenum all connected, don’t you? I’ve seen someone troubleshooting a no start condition with the intake disassembled and the MAF is so out of whack that it dies as soon as it starts. I think it’s time to get back to the basics. Fuel, air, spark. Those three requirements haven’t changed in a hundred years. Even with computer controls. I’d go in that direction.

Check the basics. Is there spark? Fuel pressure? Injector pulse?

A shorted injector will take out the quad driver in the ECM and you have 2 injectors under spec… shorted. This is a common problem on the 3.1.

You probably don’t have the injector pulse and if you don’t then the quad driver in the ECM has been taken out by the shorted injectors.

Get a injector test noid or a 12 volt test light, plug it into one of the injector harnesses, crank the engine over and see if the light pulses. If it doesn’t pulse more than likely it’s the quad driver.

In this case the fix is replacement of the ECM and shorted injectors. Given the age, mileage,and accessiblity I would replace all of the injectors.

First, the injector resistance I first posted was indeed for Injector #5, taken with a $2 voltmeter I picked up at Harbor Freight. The list of all 6 I posted were performed by the second diagnostics mechanic, and noted on my paperwork. I didn’t look up the allowances, but rather took it for what it says on the papers. I myself didn’t believe it to be injectors for the longest time either.

Basics… okay.


Yes, we definitely spark. It tries to start. Plugs fire bright and with perfect rhythm when the engine is cranked and the plug is on the block. It also purrs like a kitten on WD-40 sprayed into the throttle body. For 10 seconds anyway.

Fuel pressure?

Good when tested at the rail, both at key-on and when cranking. It doesn’t plummet like I’d expect when it stumbles and dies. Pump looks good, sounds fine. Swapped relay. Changed filter. Pump is new with 1 yr / 10,000 mi on it. Strainer is new. Fuel is correctly colored and smells normal. No visible fuel or fuel smells in vacuum lines.


Yep, again runs on WD-40. Intake attached or removed, no difference. Has a new IAC that I checked to be clean with no visible damaged. Swapped the MAF with no change, so I swapped back.

Injector pulse?

Hard to say. Would love to hook up a light, but I don’t see any way to access any injectors other than #1 and #5 without removing the plenum, and even those two are touch to reach. I just don’t have a torque wrench nor the gasket to do that on a whim. I’m amazed that the mechanic was able to get in there.

As far as why it failed after a cross-country trip, and a few hours after a CA Smog Test, I have no idea. I can only guess that the 3-minute 2500rpm test stressed something to the point of failure. It did make it about 50 miles that day after the smog test before sputtering out at a gas station (no, I didn’t purchase fuel that day).

Willey basically summed up the issue. Bad injectors = good chance of no injector pulse at all. You don’t need to get at all of the injectors to find this out. Just pull one of the ones you can get to & plug in a noid light (which you said you have).

Although, I have to say that you probably just need to junk the car or have someone else deal with working on it since you’re all hung up on doing what you need to do to get at the injectors. You can stand there and peer at them through the plenum all you want, but you won’t figure anything out that way.

Perhaps you’re just thinking “well, maybe that’s not the problem, so all that work for nothing…”

Ok - well there may be some other problem as well - but you know that you have 2 bad injectors in there. So the thing just has to come off. Period.

I don’t have a noid light, nor did I say I have one. I just researched what they were last night so I could look into getting one.

I know what I need to do to get at the injectors to replace them. What I didn’t want to do was to remove the plenum, buy the gasket, and buy a torque wrench just to be able to measure resistance of the injectors. Since the mechanic was nice enough to write them down for me (and now that I’ve found them), it’s a moot point. All the same, tearing into an engine when inexperienced is a daunting task.

The reason why I even bothered to try to diagnose this far is because the mechanic said that it wouldn’t run because of the alternator, and that it failed the smog test because of the injectors. Three alternator tests and an alternator swap proved that half of the diagnosis to be dead wrong with me by the roadside, so I indeed doubted the other half.

Willey: Is there any way to test the quad driver in the ECM? If it’s burned out, then the cost of parts alone is going to cost me what the vehicle is worth to get it running again. If it’s fine, I’ll probably move ahead with an injector swap.