Hi, Its been a while since I posted on this board. My firebird has stopped being my daily driver oh about 8 years ago, but I never could bring myself to sell it. The fuel pump went out a couple of years ago and I let the car sit for about 8 months before replacing it. The injectors have since had a sticking issue.

This may be more of a fuel pump wiring than injector problem.

Here is the list of "new"
I just rebuilt the Throttle body, with new GM injectors and all new gaskets. (I will replace the IAC valve when it comes in, the tps tests good)
New Fuel filter (after market)
New fuel pump (GM)
New fuel stranner (in tank)

The fuel pump kicks in for the 2-3 seconds when you turn on the ignition to the run position.

When the car is cold I can spin the starter for 3-4 seconds and the oil pressure will build up to the point where the injectors start firing, so I assume the fuel pump is being activated by the Oil pressure sensor/switch.

Once the engine fires it runs great (considering 212k miles on a 305).

I assume the relay is good as to the pump kicking on with the ignition switch is at run position.

The only known problem with the car is a bad EGR valve (the only code the computer is storing is the EGR) and the fan switch has gone bad, the fan switch will be replaced shortly.

What are the other components that I should look at? What tells the injectors and fuel pump to engages during starting?

Also where can you buy a new pigtail for the fuel pump relay?

 

found the relay pigtail at hawks and ordered it. So just need help with the issues.

 

found a diagram


looking at this there seems to be the fuel pump prime lead at the relay that goes off some where, this is working as the pump primes when the ignition switch is set from off to acc.

The 12+ is hot and proper voltage, the grounds test well.

so it appears to be the lead going to the computer, I will this weekend trace this wire back to the computer and test for Resistance/short to ground. If the ECM isn't engaging the fuel pump during start up, is this a bad computer or is there another sensor that tells the computer to power the pump?


Once I get these "ghost" issues worked out I am either rebuilding or replacing the 305, but I want to solve all these issues so I have a known starting point first.

 

Im lost on what the complaint is? Slow start up?

 

i to am somewhat lost as to what your asking

 

The injectors are not firing when cranking the car, and I think its due to the fact its not running the fuel pump when cranking the car. I think my main question is "is this a bad computer or is there another sensor that tells the computer to power the pump during starting the engine"

It will crank on its own if you let the starter spin until you build oil pressure and the OPS engages the fuel pump. If the car is warm, you can't build enough oil pressure off the starter for the OPS to engage the fuel pump. So yes in a way slow starting.

When the car is warm you can turn the ignition to the run position, hear the fuel pump do its 3-4 second prime. Then if you turn it over (crank the car) you see one little spray of fuel then nothing from the injector. If you pour a little gas into the TB it cranks up and runs fine, or if you manually override the fuel pump to always on it cranks fine.

 

Just realized that wiring diagram is TPI, anyone have it for the TBI?

 

The ECM activates the fuel pump relay for a 2-3 second prime when the key is turned on. There is a decay timer in the ECM that will prevent the prime sequence from taking place if the key is cycled on-off-on quickly more than once. Once the prime sequence has finished, the ECM waits to see the crank reference signal from the distributor before reactivating the relay.

Use a test light to verify the 12v signal from the ECM while cranking. Later GMs switched to using a grounding signal rather than a 12v signal. Either way it's fairly easy to verify this signal using a test light. You either attach the test light's clamp to batt + or ground. You may have a defective relay.

If the relay is not getting a signal from the ECM while cranking, you are right to check the circuit back to the ECM. You are obviously getting the crank reference signal at the ECM because your injectors are operating.

For diagrams, check the Tech info pages on this site. Better yet, find a Helm's Publishing factory service manual. You obviously are keeping this car and you want to own this book. It is the bible for this car.

 

You can look for my "Wiring Diagrams" thread in the electronics forum. There is a link to the eaglemark EFI forum where you will find a wealth of EFI diagrams.

 

Just looked at Mitchell and there is one control circuit from the ECM to the relay. If the prime function is working, then the circuit is obviously okay. It is a 12v + signal too BTW.

One thing that you may want to look at is the CRK fuse in the fuse panel. The ECM receives a 12v signal from the ign switch in the Start position without this signal the ECM is likely not activating the engine start functions.

 

Thanks ASE doc that is the information I needed, I will investigate this weekend. I am trying to avoid rigging it up. Figgured push comes to shove, I can always put a signal wire from the starter solenoid to the fuel pump relay, not elegant so I don't want to do it. I know the computers very rarely die, and its usually some other signal or wiring.

 

You are correct in beleiving that the ECMs rarely fail. Also, we want to avoid rigging our vehicles simply because it makes it difficult to diagnose issues down the road. Plus we want to be proud of our cars and the work we have done. It's hard to be proud of wires and patches strung here and there.

 

OK did some investigating last night, the relay pigtail definitely needs to be replaced however it isn't the current issue, but a new one is on the way.

The issue seems to be voltage drop during starting, I need to get it over to one of the parts stores and get them to check the starter amp and battery, although the battery is only 2 years old.

The following tests were done 3 inches below the relay plug on the wire.

If I pull the wiring harness and plug in my multimeter turn on the ignition the ecm wire is sending slightly less than battery voltage. When I engage the starter and the ecm sets the relay to power on the ecm wire is only getting 7 volts. The voltage drop is worse with the relay plug up its around 6 volts. Voltage drop to the hot wire at the relay w/o the relay is something like 11v (starter spinning) and with the relay I think it was 10.5, at the battery at the time I was seeing 12.10v ignition off and 11.3 with the starter running.

So I either have a grounding issue or some other electrical issue.

The battery cables are less than 5 years old, with factory molded on ends.
The starter is oh probably 8-9 years old. (wow how time flies)
The engine although high mileage has no smoke and the oil is clean, and runs fine so I don't think its straining the starter.

Everything seems to be worse when hot.

Does the car have a voltage regulator (not the one in the alt, but one to the computer)?

There is a little wiring block beside the battery where the fuel pump power plugs in and then goes to the fuse behind the battery on the inner finder rail, If I pull that fuse the check engine light doesn't illuminate when key is set to run (just thought that was odd).

All fuses are good in the car.

Just as a side note I did notice the electric windows have gotten exceptionally slow, so that leads back to the idea of a grounding issue. Where should I investigate to check for proper grounding?.

My multimeter can do up to 10A draw tests so I will put it inline to the fp relay and ECM to see if maybe the relay is just drawing too much amperage, but the sharp voltage drop out of the computer is a concern. I will test the voltage at the computer sometime today.

Oh how I hate electrical issues.

 

I cleaned up the relay wiring the voltage drop is less now but still a concern, it is worse when I allow the car to get to 220 degrees. In fact I discovered the OPS has a temperature fault and stops powering the fuel pump when its hot, the oil pressure is still around 30psi when hot so I think its the switch in the OPS, or the voltage issue I've noted.

Also what is this wiring block's part number, Its a little warn and since its right beside the radiator it may be part of the heat related voltage drop.

I tested the alternator and it tested good using my altanator tester, and also with a clamp on amp meter I was getting around 70 amps, its capable of doing 100 amps but I don't think it does unless there is demand.

Starting the car the starter only drew 220 Amps using a clamp on amp meter on the positive battery cable.

The battery is on the charger right now I gave it a lot of a work out tonight, I will take it by Autozone and have them test it tomorrow.

I am starting to wonder if it could be a bad fuse block as the interior light seems to flicker dim and back bright if you turn on anything else in the car.

I'm truly lost on what to test next.

 

That part is a junction block. It looks real dirty. You need to verify good clean wire connections there and everywhere else between the battery and the ECM. For grounding, check the connection to the block from the batt-. Also check the ground strap from the block to the body at the rear of the pass side head. Check the grounds at the rear of the pass side and driver's side heads. Definitely check the amp draw to the relay coil. It may be partially shorted and drawing high current. You can also check this by swapping the fuel pump relay for the MAF power relay. Check the relay numbers to be sure they're the same.

 

Yes its really dirty, I only put 250 miles on the car last year and about the same the year before just doing occasional trips around the house, and thus haven't been keeping it as clean as I should. The only rust on the car is right there around the battery, although the paint in the engine bay is getting pretty bad.

Tracing the wiring diagrams I see there is a signal wire between the computer and the starter solenoid does that have anything to do with the fuel pump within the computer controls. The manual calls it the "crank signal".

My plan although probably next weekend is this.

Verify the grounding as you suggested, and disconnect each point and clean the contacts and reassemble. (although I tried a temp ground wire from the battery to the engine block)

Will be taking the junction block apart and cleaning it, the battery cables are clean and the battery contacts are clean.

I'll probably take the wires loose at the starter and clean and reinstall.

I see that there is a +12 that splits out and goes to the computer, fp relay, and ops from the junction block, through a 20amp fuse. Is this the voltage that the computer in turn feeds to the relay to enable the pump, or is it using the computers main 12v source?

Stupid question what switches the power on to the fuse block? I am seeing a major voltage drop throughout the electrical system when the starter is engaged. I don't recall if the ignition switch handles it, or if it engages a relay to supply +12 to the accessories within the car.

If cleaning up the contacts doesn't help, my next plan is to start at the battery and work forward testing for the voltage drop, what points do you suggest primary targets?

 

The crank signal is used by the ECM as part of the fuel pump relay testing. It is also used when in limp mode for cranking enrichment.

This is the main power feed to the ECM. The IGN+ to the ECM goes to the power control chip.

Switched ignition power to the fuse block is via the ignition switch. No relays involved.

To test for where the voltage drop occurs, connect a DVM on the volts scale between two points in the system. Such as at the battery - terminal and the engine block. Then crank the starter over. More then a 1/2 volt and you found a problem.

Can do the same between the battery + terminal and the starter lug. Then between the starter lug and a location on the fuse block, and so on.

Note that there are three or four fusible links on the starter lug. These feed to various areas of the cars electrical system.

RBob.

 

Also where is the junction for this split in the wiring harness?

BTW RBob checked your site, very impressive what you have done to the OBD computer.

 

The '92 Camaro FSM shows it in the wiring harness behind the strut tower. Basically RH side under the hood to the rear of the engine compartment. The picture points to the location where another section of harness T's out and goes toward the front of the car.

Not sure if it is in the same place on your car.

Thanks, it has been keeping me busy.

RBob.

 

Rbob has provided a very good explanation of the volt drop test.

 

thanks for all the help guys I will get back to you when I get a chance to dig into it again.

 

Ok, pulled apart the wiring at the battery cleaned all the connectors, and at the junction block, pulled the ground wires and cleaned the contact points.

Replaced the fuel pump relay pigtail.
Replaced the fuel pump relay.

Car starts up normally, but after getting it warm it would not still.

So I disconnected the oil pressure switch and it would start up without any issues hot or cold. So I replaced it and now the car starts up nicely. It seems it was faulting around 220 and causing a short in the circuit.

I still have a major voltage drop on the ecm to fp relay during cranking its around 9v but the new relay engages with less voltage than the old one. The +12 at the relay is within .5v of the battery voltage during cranking, strictly speaking this should be within .2 but close enough.

Question has anyone ever tested the voltage here (+12 and ecm signal at the relay) if so what was it during cranking the car (spinning the starter).

I wanted to pull the computer and test the +12 and see how much voltage drop I'm getting at the computer but ran out of time.

I think the computer may be the cause of the under volt at the relay, but for now I will live with the voltage drop, I'm just glade I can drive the car and not have to pop the hood to crank it. It will never be my daily driver again but at least now I can trust it to do some weekend hops.

 

Because of the transistor in the ECM that drives the FP relay there will be some additional drop. A half volt wouldn't be out of the question.

RBob.

 

I'm not so worried about the +12 at the relay being off its within reason, its the ecm to relay wire, when cranking the car its dropping to 9v still (at battery with starter running its 11.6, its 12.5 with the switch off). And when the car is running its around 10.5-11v so the computer is eating up a lot of current in its internal switching, assuming its getting proper +12 current. When I get a chance I'll pop the computer out and test its in voltage, if its proper then I know I have a issue in the computer.

I'm pretty good with electronics I build Arduino circuits and computers for a hobby. So if it turns out the be the computer I should be able to repair it. Assuming its only a single or double layer board inside of it. If not the reman computers are relatively cheap for these cars.

 

could be having a vats problem.the eprom in the ecm controls two things 1)start enable. 2)fuel injector firing.

 

VATS checks out, I've got the car cranking and running correctly. The voltage is just a little lower than I would like at the relay. Since that wire goes from the relay to the computer its going to either be an issue with the wire or the computer.

 

dvom and a wiggle test on the wire from fp relay to ecm.also try unplugging the two harnesses to the ecm 2 or 3 times as this may correct your problem.good luck.