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Arench
Arench, Master Technician
Category: Pontiac
Satisfied Customers: 1490
Experience:  30-years experience auto and truck repair.
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Pontiac: 85 Pontiac Fiero, 2.8, 6cyl. GT, manual trans. The

Customer Question

85 Pontiac Fiero, 2.8, 6cyl. GT, manual trans. The fuel injectors are pulsing simultaneously. Rather than alternating. All grounds have been checked. Have not been able to find any shorts anywhere. Two computers are being used to test with the same result. The tan ground wire, C1/D6 on the computer connection has a very high resistance. Your thoughts?
Submitted: 1 year ago.
Category: Pontiac
Expert:  Arench replied 1 year ago.
Good morning this is Mike again. This is normal operation.This system is a simultaneous injector fire even though there is a two bank electrical scheme.Half the fuel charge is delivered per revolution.
Customer: replied 1 year ago.

Are you saying that 3 of the injectors are pulsing together while the other 3 are not? Then the other 3 pulse? so, it goes back and forth? What about the tan ground with high resistance?

Expert:  Arench replied 1 year ago.
All 6 injectors spray at the same time, therefore the term simultaneous. Half the fuel charge is delivered to the intake valve per crankshaft revolution. Grounds can not be resistance measured on a car. Grounds must be voltage measured when active (under load). Expect grounds to have 100mv or less when hooked up and active. If the ground circuit reading is not close to zero then replace the circuit or "back it up" it a new ground wire added to the circuit.Some good learning about this car can be found here:http://www.pontiacperformance.net/techarticles/osg/FI.html
Customer: replied 1 year ago.

Is there any way that the entire fuel charge can be delivered to the intake valve accidently?

Expert:  Arench replied 1 year ago.
It's not likely.Perhaps if the car has wrong injectors delivering too much or the computer has too long a duration by double on the injector pulse. I think you should start at step 1 by measuring voltage on the grounds at the ecu with engine running. Write it all down. Record circuit number and voltage.
Customer: replied 1 year ago.

Thanks. I'll get back to you in a day or two.

Expert:  Arench replied 1 year ago.
Good luck, I know you will figure this out in time.
Customer: replied 1 year ago.

Hello. Just to let you know I haven't forgotten you. We still have not found the problem yet. Will let you know when we do. Thanks.

Expert:  Arench replied 1 year ago.
I'm hopeful you will get it working. It might be useful to have a scan tool that works with this car as I have not heard mention of any fault codes.
Customer: replied 1 year ago.

The only consistent code is for the coolant temp. sensor. The one in there now is new.

Expert:  Arench replied 1 year ago.
measure voltage at both wires at the coolant sensor with key on and report here. faulty coolant sensor value will make the car burn too much fuel.
Customer: replied 1 year ago.

Thanks. I will. But it won't be 'till Monday. It's my next day off. How about a MAT sensor?

Expert:  Arench replied 1 year ago.
Oh no, we are going to focus on our friend the coolant sensor only. No progress can be made until that code 15 is gone. There is a fish on the hook and it's going to get our full attention.
Customer: replied 1 year ago.

I got lucky. Here's the info. you want. Battery voltage is 12.22 with charger on. Yellow wire is 4.75 volt and black is 0.00 volt.

Expert:  Arench replied 1 year ago.

This is the wrong reading with it plugged in. With that reading the computer thinks the engine temp is -40f (fault minimum).

Make sure its plugged in for readings. Replace coolant temp sensor and wire connector with new parts and retest.

Expect to see 1.5 to 2.0 volts with it plugged in. Hotter engine lower volts on yellow wire.

TX3 sensor and TX3A connector (standard ignition)

Customer: replied 1 year ago.

I unplugged the wire from he sensor and tested it for the readings I sent you. I'll try it again with wire connected. The sensor is brand new. I'll have to wait till my day off to change the wire.

Expert:  Arench replied 1 year ago.
For future reference always measure circuits with EVERYTHING put together unless otherwise instructed. The point was to see the coolant sensor voltage reading (it has to be plugged in for that!)
Customer: replied 1 year ago.

I plugged the wire onto the sensor. With a battery voltage of 9.69. I measured 1.9 volts on the sensor wire.

Here's a separate problem on another car, if you want it. Of course, I'll pay extra for your help. I've already decided to pay you in full regardless of the outcome with the Fiero since you've been of great help. I just want you to hang with me until the end. Any way, I have another car, a 1979 AMC Pacer. I put the multi meter to the charging system. It's only charging at 11 or 12 volts. So, I went and got a new alternator. It's charging at about 13 volts. The battery and wires are all new. I go back to the auto parts store. They test it in the car and now all of a sudden it's charging at 14.5 volts. Later on in the day the battery was dead. What do you think?

Expert:  Arench replied 1 year ago.

it sounds like it was charging but you may have a battery drain. It must be a big drain to kill a new battery that quickly. With everything in the car turned off perform a battery draw test by putting a teslight in between a battery terminal and the battery. If the light lights up then there is a draw. Remove fuses one at a time until the draw goes away then figure out what is on that circuit that would be drawing power with the key off. If all fuses are out and there is still a draw look at unfused items like the alternator itself.

As for the fiero, charge the battery and recheck and record the coolant temp voltage (both wires) with engine running. Recheck for codes in the computer record and report codes.

Customer: replied 1 year ago.

Will do.

Expert:  Arench replied 1 year ago.
okay, good luck.
Customer: replied 1 year ago.

Hi. It's me again. I think I spoke too soon. Car running rough and coding 14 and 15. Friday I will get you the voltage you were asking for.

Expert:  Arench replied 1 year ago.
wow 14 and 15, cts high and low! best check ecu connectors and measure cts voltage there also.
Customer: replied 1 year ago.

The car is back at my house, now. So, I'll do the work. Can you tell me exactly how to do these things? I have a good multi meter. I set it to 20 volts DC. Correct? Then what?

Expert:  Arench replied 1 year ago.
Print this if you don't have one
Expert:  Arench replied 1 year ago.
Ground the multimeter to a good clean ground, use a file if you have to and make a list of every ecm terminal appearing in the graphic and record the voltage of each by back probing with engine running and everything hooked up. Mechanic should have done this already as step one. Post a graphic or transpose every reading here. I'm especially interested in the ground at A1, D1, D6, D12, D13,
Customer: replied 1 year ago.

Exactly where do to touch the red probe? Right at the ECM/wire connection?

Expert:  Arench replied 1 year ago.
to the back of each wire at the ecm where it contacts the metal terminal. look: http://2.bp.blogspot.com/-hbcsbSauW8s/TtXm_mWkxOI/AAAAAAAAADk/k9r9VvMb4Aw/s1600/back+probe.jpg
Customer: replied 1 year ago.

That's what I was thinking. Thanks. I'll have the info for you Friday. Talk to you then. Good night.

Expert:  Arench replied 1 year ago.
okay good luck, again.
Customer: replied 1 year ago.

Hello. I need to let you know, I won't have those numbers until Monday. I have to work Fri. Sat., Su.. Get back to you on Monday. Thanks for your patience.

Expert:  Arench replied 1 year ago.
It's all good. I plan on living at least until then.
Customer: replied 1 year ago.

You know, just before I sent you that message, I was thinking ' My God , I hope he doesn't die before then! Then again, I hope I don't either!

Expert:  Arench replied 1 year ago.
LOL it's a plan then.

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