I have a 1984 SE w/2.5L. The TBI injector is not getting a signal to open.

I have gone through the Factory Manual diagnostics including:

• Observe the injector during starter cranking - no spray
  
• Check fuel pump pressure - good
  
• Manually jumper the injector - good spray - injector good
  
• Probe circuit 439 (red wire) at the injector for voltage - ignition on - good voltage
  
• Test light the injector plug during cranking - no light - no signal
  
• Probe circuit 439 (PNK/BLK wire) pin 16 at the ECM - ignition on - good voltage
  
• Probe circuit 467 (BLU wire) pin 8 at the ECM w/injector plug connected - ignition on - good voltage, injector drive circuit OK
  
• Probe circuit 450 (BLK/WHT wire) pin 12 at the ECM - good ground
  
• Probe circuit 453 (BLK/RED wire) pin 3 at the ECM - good ground through distributor
  
• Check AC voltage circuit 430 (PPL/WHT wire) pin 2 at ECM - during starter cranking - 1.7 volts, good
  
• Probe circuit 430 (PPL/WHT wire) pin 2 with test light - 12 volt contact, injector cycles - ECM injector circuit OK
  
• Replaced distributor ignition module - no change
  
• Replace ECM with unit from PFF member - no change
  
• Manually priming the TBI - engine fires off and runs
  
• Manually jumping the TBI injector with ignition on - sprays - engine runs when cranked
  

I'm stumped as to what else I can check. It "seems" to me the ECM is not getting the reference pulse from the distributor module, but all my diagnostic checks would seem to indicate that circuit is good and the module is supplying reference voltage.

Any suggestions?

Marc

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Marc in sunny Titusville, FL

• 84 SE son's car, loaded
  
• 85 Coup w/V6 transplant
  
• 85 GT newly on the road
  
• 86 SE/GT "The Chameleon" - big plans!

How did you check the fuel pressure, and where?

Did you check the diaphram ?? this is common cause of 87, 88 TBI malfunction,on Fiero space craft ..it is a pain in the spleen to check because easy to damage.it only takes a barely visible slit to bring proper fuel flow to stop.
the 84 to 86 has a different style regulator but My guess! the problem is there,, Hmm better read post again..
edit,,looked at the manual,,it seems you can remove the plate and eyeball the spring and diaphram or what passes for one .
you have to hold pressure against the spring while you remove plate..it is easy to damage this style Diaphram
this kit was available at auto parts stores in 2002 for 87,88 and a kit for 84 to 86 ,,but the early models may be difficult to find now ..

[This message has been edited by uhlanstan (edited 01-24-2010).]

You Are getting an actual reference signal? You sure? Wire and module is ok but is only 1 part...
Test spark.... No spark? Look oil fill hole and see if valve rocker is moving during starter is on. No rocker movement? Bad cam gear. Is rocker movement? Bad distributor.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

I once had the same problem in an 84 Fiero (duke).Well it turned out that the brown wire at the coil pack had broak at the metal tab,that holds it on.The only thing that was holding it on was the brown plastic insulation.Try testing that wire or a jentle tug.The other sugestions are good allso.Might be the fuel pump relay (do you hear a buzz when you turn the key)?.

Glad to see lots of inputs. I really need help on this one.

To answer some and clarify:

quote From TopNotch on 01/24/2010 How did you check the fuel pressure, and where?

I checked the fuel pressure at the throttle body with a pressure gage. I should note that as a part of the repairs I was doing, I installed a new fuel pump, pick-up screen and fuel filter.

quote From uhlanstan on 01-24-2010 Did you check the diaphram ?? this is common cause of 87, 88 TBI malfunction...

Again, I have good fuel pressure. Note in my diagnostics I can turn the key on, hear the fuel pump run, see it build pressure and if I "manually" jumper the TBI injector it pulses and I get good fuel spray. If I follow through with crank starting the car with the key, the motor starts and runs until that initial prime of gas runs out. The TBI injector does not pulse on it's own however, and doesn't want to pulse even if I prime the engine with gas and start it.

quote From theogre on 01-24-2010 You Are getting an actual reference signal? You sure?

That's kind of my question now. As I followed the factory manual diagnostics, I applied a test light at the throttle body plug. Cranking the engine at the key, I'm not getting a "blinking" light which would tell me the ECM is pulsing the injector. If I check the 439 circuit (red wire at the injector plug) I "am" getting 11 volts with the key on. The power is there.

There is another diagnostic that checks the 430 circuit at pin 2 on the "Black" ECM plug, which is the distributor side plug to the ECM. According to the manual, with my test meter set to 2 "AC" volts I should get .7 volts AC or better while cranking on this circuit. I'm reading 1.4 volts AC during cranking. From what I "understand" (and at this point I'm only guessing). The "reference" signal from the distributor is in the form of voltage to the ECM. It doesn't seem to be an actual "pulse". If I understand correctly what the ECM should be doing at that point, it should be reading the fuel tables and pulsing the injector based on those tables and the inputs from it's various sensors. I'm guessing this "reference" voltage signal from the distributor is either "power off" - no reference signal, or "power on" - reference signal? I'm definately getting power from the distributor on this circuit when I crank.

I've swapped out ECMs. I suppose I could have 2 bad ECMs, but what are the chances? How can I actually test the ECMs?

The spark side of the distributor seems to be working, as I've said previously, if I manually prime the TBI, either by dumping gas down it. or manually jumping the injector after keying the fuel pump on, the engine starts and runs until it uses up the gas prime.

If I understand how the injector circuit is supposed to work, when the circuit is initially keyed "On", the ECM should pulse the injector enough to supply gas for the engine to start. Once sufficient RPM's are attained, the distributor module is supposed to turn control over to the ECM to then continue to control fuel through it's sensors and fuel tables?

I've changed modules in the distributor and also had both bench checked and they both show good. The distributor was also recently completely rebuilt includinng a new pick-up coil. The car has been driven for awhile on this distributor. By the way, the timing gear is good (I just replaced it) the distributor turns and the rockers move. Again, the engine runs when primed.

What I haven't found in any research, is a way to actually test the ECM itself?

quote From James Bond 007 I once had the same problem in an 84 Fiero (duke).Well it turned out that the brown wire at the coil pack had broak at the metal tab,that holds it on.The only thing that was holding it on was the brown plastic insulation.

I found exactly that same problem about a year ago on this car after degreasing the engine and having a "no start". I've soldered new connections on those terminals, and checked them again now with this problem. Must be a common break point.

Keep those cards and letters coming folks, I'm baffled by this, and obviously, the car's not being used! Once I solve this, I promise to post the results, even if it's through some error I've made.

Hey, that's how we learn, from our errors!

Marc

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Marc in sunny Titusville, FL

• 84 SE son's car, loaded
  
• 85 Coup w/V6 transplant
  
• 85 GT newly on the road
  
• 86 SE/GT "The Chameleon" - big plans!

Bump to the top...

Probe circuit 439 (red wire) at the injector for voltage - ignition on - good voltage
Test light the injector plug during cranking - no light - no signal


Sounds like the PCM is not grounding the injector.
If you had a breakout box I would say probe the PCM directly to see if it's giving a ground.
Sinec you don't (I'm guessing) then next check resistance of the ground ckt back to the PCM to verify the wire,if it's good but you don't get a ground from PCM then more than likely PCM injector driver's are failed.

I don't know crap about these particular engines,and have no idea if there is a subsystem that when faulted would cause the PCM to not fire injectors.
Some vehicles will not fire injectors if it know's there is an ignition system malfunction.
ie no ignition fire so the PCM shuts down fuel injector to corresponding cylinder,vortecs and taurii do it to name a couple.

quote From DefEddie on 1-25-10 Sounds like the PCM is not grounding the injector.

I agree. That's the conclusion I'm coming to. The thing that bothers me is that I picked up a second ECM and it does the same thing! That makes me suspicious there might be something else wrong.

Currently I've pulled the distributor and am carefully going over all the wires. When I replace it I'll check the ECM ground again like you've suggested. I'm suspicious too that it's a "ground" problem.

I'll keep all of you posted on my findings. Thanks again for the inputs.

Marc

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Marc in sunny Titusville, FL

• 84 SE son's car, loaded
  
• 85 Coup w/V6 transplant
  
• 85 GT newly on the road
  
• 86 SE/GT "The Chameleon" - big plans!

quote Originally posted by Gwain: I agree. That's the conclusion I'm coming to. The thing that bothers me is that I picked up a second ECM and it does the same thing! That makes me suspicious there might be something else wrong. Currently I've pulled the distributor and am carefully going over all the wires. When I replace it I'll check the ECM ground again like you've suggested. I'm suspicious too that it's a "ground" problem. I'll keep all of you posted on my findings. Thanks again for the inputs. Marc

Not the ECM ground,I meant the actual pin that goes into the pcm from the injectors.
One side of the injector is spliced to vpwr that goes to all injectors,it is actuated by the other side that is grounded by the pcm.
If it's not grounding then it is more likely internal to the pcm and not just the ECM ground.
If the ecm ground is bad enough to not allow ground to injectors your going to see alot of other stuff not working.

Again,going off basic OBDII type knowledge so make sure it applies in this case (i'm sure it does,never seen it done any other way really)

DefEddie:

I guess I'm not following you here. When you refer to the "PCM", what are we talking about?

The single throttle body injector has a 2 pin connector. One of the lines is tied into the same circuit for power as the ECM. Probing that circuit I have power to the injector and power to the ECM. So I know that circuit is good.

The other side of the injector harness goes back to the ECM plug. If it's grounded, the injector opens. I've tested that circuit at the ECM plug, and the injector opens if I ground the lead. That leads me to suspect that something internal to the ECM itself is not providing the "ground".

I don't recognize the term PCM, and I don't know of anything else in the injector harness circuit in between the ECM and the injector?

Marc

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Marc in sunny Titusville, FL

• 84 SE son's car, loaded
  
• 85 Coup w/V6 transplant
  
• 85 GT newly on the road
  
• 86 SE/GT "The Chameleon" - big plans!

Powertrain Control Module? In any case, DefEddie is speaking generically, so disregard.
If you have access to an oscilloscope, monitor each injector pin while cranking. If your injector is activated by grounding one pin while another has steady voltage applied, you should only see pulses at the grounding pin. If you see them at the other pin, you have a voltage supply problem. If you don't see them at either pin, you aren't getting the grounding pulses.

Yeah,sorry-I mean the ECM.
ECM refers to electronic/engine control module,which generally only control's the engine.
I deal with newer stuff so we call it a PCM-powertrain control module which has trans and engine control functions.


Your getting what i'm saying though.
Exactly like you said,the ECM is not grounding out the injector.
It is either due to a faulty injector driver module in the ECM,bad circuit to the ECM from injector or something is causing the ECM to not ground the injector.

I don't believe the older ECM's will shut off fuel like the newer ones because of no spark,so I would probrably disregard option 3.
Option 1 means a new ECM,but not until you verify option 2 is not the cause.

Basically all you need to do is verify the wire from injector to the ECM (ground) has .5 or less ohm's of resistance.
If it does than the only option is the ECM.

Remember after doing all your checks though to reassemble everything before you replace the ECM.
If it was a faulty connector or pin positioning than all will be well. (this has happened to me a number of times.)