Sarah's 1991 Camaro

TransAmDan

Forum Admin
Staff member
It's all working progress. I may find once the ECU earth is looking good there will be another area to improve on. Was hoping to get some time on it tonight, but some work has come up that will consume my evenings until the weekend.
 

Will

Core Member
If I pull the injector it can't fire anything as no fuel can be connected to it.
The oil pressure sender dosn't appear to be causing any issues. There is 12V on the injector, the other side is pulled to ground from the ECU which isn't reaching true ground, its about 4 volts off, indicating a bad earth somewhere.Still searching for that earth, which is why my next step is to check the ECU earth while cranking. As earth are saying zero ohms, but this is when there is no load, pretty sure there is a rotton one when pulling current.
Absolutely Dan...if the oil pressure switch circuit was causing the ECU to inhibit fuel injection, there would be no waveform accross the injectors, not a low amplitude one. I'd say don't waste your time looking for fuel in the cylinders, you've already proved that there isn't any.
 

Will

Core Member
You could ultimately have a fault with the fuel injection firing side of the ECU. If so, it might be worth having a crack at repairing it as it's not overly complicated. I have been looking at various injector switching schematics on the web. I couldn't find one for the Camaro (and I'm guessing the wiring diagram in the manual probably doesn't show the inside of the ECU anyway?).
Firing the injectors by grounding them seems to be a standard way of doing it. Most systems appear to have a low value resistor between the switching transistor and earth, presumably to limit the current through the transistor. If the resistor was to go O/C or fail high, this would stop the injector being pulled to ground and from firing. Some system have separate resistors for each transistor and it would obviously be very unlikely for all 6 to fail. But some have one common resistor in the ground line for all of the transistors. If the Camaro's ECU is like that it may be something to consider.
 

TransAmDan

Forum Admin
Staff member
You could ultimately have a fault with the fuel injection firing side of the ECU. If so, it might be worth having a crack at repairing it as it's not overly complicated. I have been looking at various injector switching schematics on the web. I couldn't find one for the Camaro (and I'm guessing the wiring diagram in the manual probably doesn't show the inside of the ECU anyway?).
Firing the injectors by grounding them seems to be a standard way of doing it. Most systems appear to have a low value resistor between the switching transistor and earth, presumably to limit the current through the transistor. If the resistor was to go O/C or fail high, this would stop the injector being pulled to ground and from firing. Some system have separate resistors for each transistor and it would obviously be very unlikely for all 6 to fail. But some have one common resistor in the ground line for all of the transistors. If the Camaro's ECU is like that it may be something to consider.
Yes very possible. The ECU has 2 switched outputs for the injectors, one for each side. When looking at the volts it's switching the neg side seeing 8 volts across the injector. It dosn't appear to be switching complely to ground. Once ECU ground checked/sorted and still not working the next step is checking for a failed component in the ECU. It's old tech nice big components. Should be easy to put in a modern MOSFET or something similar, I actually have tubes of them laying about in the TO220 package.
Tech from early 90's
IMG_20201011_131958.jpg
 

AmericanThunder

Super Moderator
The point is it won’t switch the injectors to ground unless pre-conditions are met.
Those are:
1: it see’s a signal indicating that the fuel pump is running during cranking
2: it see a signal from the oil pressure switch to indicate pressure

Page 6-101 if you have the Chiltons manual
Page 10-20 if you have the Haynes manual
For the pin outs to test.
You are checking for a ground issue you may or may not have but the operation of essential items to test has not been done.
Put your scope on the pins indicated and tell us what you find.
 

TransAmDan

Forum Admin
Staff member
The point is it won’t switch the injectors to ground unless pre-conditions are met.
Those are:
1: it see’s a signal indicating that the fuel pump is running during cranking
2: it see a signal from the oil pressure switch to indicate pressure

Page 6-101 if you have the Chiltons manual
Page 10-20 if you have the Haynes manual
For the pin outs to test.
You are checking for a ground issue you may or may not have but the operation of essential items to test has not been done.
Put your scope on the pins indicated and tell us what you find.
Yes good valid points and things to test. What I have found so far is the ECU is trying to switch to ground on the 2 injector control pins, but it dosn't quite make it like its not strong enough to do so. it gets about 4 volts away from ground.

Measured an injector ohms this morning, its 12.1ohms for the easist to get to injector. Joined one of its pins to ground, and the other side using an volt meter in current mode and a probe on battery+, connected to the other side of the injector I could hear a faint click, and draws just over 1Amp. Think there is a good chance the injector is working. What is dosn't rule out is a blockage in the fuel rails.

Got more hardware coming today, for firmware development, so I may not be able to get back out in the garage until Friday.
 

AmericanThunder

Super Moderator
Yes good valid points and things to test. What I have found so far is the ECU is trying to switch to ground on the 2 injector control pins, but it dosn't quite make it like its not strong enough to do so. it gets about 4 volts away from ground.

Think there is a good chance the injector is working. What is dosn't rule out is a blockage in the fuel rails.

I suspect the reason the ECU doesn’t ground the injectors is because other conditions are not met.
My other suggestion was to crudely test the injectors in-situ.
A fuel pressure gauge would help too if you can borrow one?
 

saleen 192

Core Member
Tow the car to Wales lol oh shit we are in lockdown Friday tow to to 3 bridges then lol
 

TransAmDan

Forum Admin
Staff member
The point is it won’t switch the injectors to ground unless pre-conditions are met.
Those are:
1: it see’s a signal indicating that the fuel pump is running during cranking
2: it see a signal from the oil pressure switch to indicate pressure

Page 6-101 if you have the Chiltons manual
Page 10-20 if you have the Haynes manual
For the pin outs to test.
You are checking for a ground issue you may or may not have but the operation of essential items to test has not been done.
Put your scope on the pins indicated and tell us what you find.
I have the 1991 Camaro Service manual.
Looking under the V6 Multiport fuel injections VIN code T
There is no oil pressure switch going to the ECU, nor is it in the circuit, the +12 comes from the fuse to the injectors, the neg side come from the ECU. So on this model the oil pressure switch dosn't appear to play a part.
For the fuel pump, there is an output to control the relay, and a signal labelled 'fuel pump control unit' this is a grey wire to indicate the fuel pump has power. I can check that.. There are 3 wires going to the pump, +12V, 0V and fuel sender level.
 
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Will

Core Member
The point is it won’t switch the injectors to ground unless pre-conditions are met.
Those are:
1: it see’s a signal indicating that the fuel pump is running during cranking
2: it see a signal from the oil pressure switch to indicate pressure

Page 6-101 if you have the Chiltons manual
Page 10-20 if you have the Haynes manual
For the pin outs to test.
You are checking for a ground issue you may or may not have but the operation of essential items to test has not been done.
Put your scope on the pins indicated and tell us what you find.
I agree, anything the ECU needs to be present to fire the injectors should be checked for. My point was about how it inhibits injection activation? Assuming something is missing, electronically speaking it seems strange for there to be any waveform at the injectors at all if they aren't supposed to be firing. That was all.
 

TransAmDan

Forum Admin
Staff member
Grey wire pin E13 on the ecu, fuel pump feed back goes high when key turned to first position for a few seconds. then goes high during cranking.
 

TransAmDan

Forum Admin
Staff member
1603214512355.png
signal from the vats system. 20ms per division. Frequency is 29.12hz. Is this what we expect from the vats system. The security light does go out on the dash.
 

TransAmDan

Forum Admin
Staff member
Injector pulses, got two traces here, Red and Blue, it appears red and blue are the same waveform.
1603215071334.png
pulling it very close to 0v now with a better ECU earth. still no go. 50ms per division.

Perhaps the injectors working fine and there is a flue blockage, odd that all 6 should be effected.
 

AmericanThunder

Super Moderator
This may help. It’s a V8 Tahoe but the circuit design and even the colours of wires used is identical.

I’m assuming the car has an oil pressure gauge?
 

TransAmDan

Forum Admin
Staff member
Red signals is the injector control signal. Happy that the injector control is getting near to zero. There should be anough voltage across this now for it to fire.
The blue trace is Spark timing Output signal. appears to be only reaching 1 volt, not sure if this is correct, which is why i tried to fire the car up with carb cleaner to probe spark is present.
1603215726716.png
The above signal is when turning the key with carb cleaner in the intake manifold.

1603217987864.png
 

AmericanThunder

Super Moderator
Rockauto list an oil pressure sender for the car.
Located next to the oil filter?
Pin e13 / grey is correct. What are pins B1 and C16 doing?

But this looking good to me, so we are back to fuel delivery. You really need to verify fuel pressure at the rail and an injectors ability to deliver. If fuel pressure is ok I would think it’s worth throwing money at the regulator.
 

TransAmDan

Forum Admin
Staff member
Both my circuit diagrams and the one I found on-line show the oil pressure switch and concur on the pins they use.

Ah, tested the Grey wire some time ago, i saw Fuel Pump, and sent with that, didn't see it said Oil Pressure below it.
1603218068854.png


1603218141885.png

I can hear the pump prime and checked voltage when cranking, the fuel pump stays active. Think we are all good there.
 

TransAmDan

Forum Admin
Staff member
Rockauto list an oil pressure sender for the car.
Located next to the oil filter?
Pin e13 / grey is correct. What are pins B1 and C16 doing?

But this looking good to me, so we are back to fuel delivery. You really need to verify fuel pressure at the rail and an injectors ability to deliver. If fuel pressure is ok I would think it’s worth throwing money at the regulator.
Yes, that's my thought pattern too. I am happy the electrics are looking good now. Earth improvements to the ECU has given a better switch to the Injector.

I know there is pressure in the fuel rails, but how much pressure I do not know. I can say a quick short press on the Schrader value squirts fuel and hits the bonnet. So pressure at one end of the rail, but why not getting to the injectors? perhaps a blockage? Fuel turned to sludge? I haven't found more info on the regulator yet. It is a tiny hole, surely that isn't all the fuel the car needs comes through that tiny pin hole? Is the regulator like a secondary carb? only kicks in when extra fuel is needed and there is enough base fuel when it is closed?

B1 and C16, I haven't checked since the ECU ground improvements, there were measuring around 12V and dropped a little while cranking. I could measure again.

Maybe worth taking the fuel rail off and giving bits a clean, check all the internal can pass fuel through them. Exhausted many other things now. Always great to prove things it not, then it makes more certainty to what it is.
 
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