My car gave out on me one day, i drove it home fine and the
next day i went out to start it up I couldn't get it to do anything
but run a second or two and then die, I replaced alot of parts
and still got no where, I even checked for error codes and nothing
would come up, I finally broke down and took it to chevron
to have them take a look at it, they told me the injectors were
staying wide open and dumping too much fuel to the point of
where it was filling my oil up with fuel, so they said it was
the fuel pressure regulator, they changed it and it did the same
sh*t, so they said the only other thing it could be is the computer
and then they told me they wanted $650 to change it! I decided
to take my car back before anymore damn part changes that
aren't fixing sh*t. Anyway I've looked in to doin the computer my
self its only $152 after the core exchange and it only took me 5
minutes to pull, I am gonna hold off a little while though before
i buy the new one because i'm not sure i can trust chevrons
diagnosis.... ANYONE else have any suggestions??

 

Yukon,

ECM's rarely go bad. It happens, but they get blamed for failure a lot more often than they actually fail.

Do some diagnosis first. Did the technician tell you how he/she determined that the injectors were staying open?

There are two ways injectors can be open all the time. They are either mechanically stuck open, or are being held open electrically (by the ECM or wiring). Presuming they are right, and the injectors are being held open electrically, the ECM isn't the only possible cause.

If it were the fault of the ECM, four of them would stay open, not just one. The injectors are batch-fired in banks of four (keft and right). The 12VDC power source is routed to the injectors when the ignition is ON. The ECM provides the ground path for the injectors to complete the circuit and operate them.

This means that any grounding in the negative side of the injector circuit will cause the injectors to open. Grounding can be caused by a wire that is pinched or has the insulation worn through. Grounding can also be caused by a failure of the ECM switching transistors for the injector circuits. Grounding can also be caused by a single injector that has failed and has the solenoid coil shorted to ground.

If you suspect that injectors are staying open you can use an ohmmeter to perform some simple diagnostics:

1. Disconnect the injector electrical connectors and test the resistance of the injector coils between the two pins. This should yield a reading of between 12-18 ohms.

2. Test the resistance of each injector pin to a good engine ground. You should get no reading (infinite resistance).

3. Meter the wiring harness for shorts to ground. With the ignition off, the ground side of the injector harness should be at least 40 ohms to ground.

If everything checks out, chances are you don't have an electrical problem with the injector circuits. If you do find a suspect injector, keep it unplugged and try starting the engine. It will run a little unevenly since one cylinder will be getting no fuel, but it should be a LOT better than before. If this is the case, you have identified an injector that needs a replacement.

If you have a fuel pressure gauge, you can test the system pressure. If the pressure drops within 90 seconds after turning off the ignition switch, you probably have a leak, and it isn't an electrical nor ECM problem.

Let us know what happens from there.

You stated that you replaced a "lot of parts". What exactly did you replace, so that we don't spin our wheels here?

And, for the record, what year/engine/fuel system do you have?

 

AK TA,

when did it start giving you fits??? what was the temp (ambient)...

this is an "89 5.7l l98 tpi" right??? no cold start injector...

any one know off hand what controls cold start enrichment on one of these??? I have seen a whacked out CTS blow black smoke like a mother on cold start in cold temps... fouled the plugs and then become a general PIA...

set up some perameters of when and how the condition came to be...

the climate you live in is hard on cars...

zroc

 

I had a similar problem wiht my Z. My AFPR was dumping tons of fuel into the crank and the engine would not turn over. The fuel filled the cylinders and i had to remove all plugs and replace the oil and the fuel pressure regulator.

 

Craiger,

I remember your "holy regulator". If you look closely at Yukon's original post, he said the shop already changed his regulator, so I doubt that's it.

You still with us, Alaska?

 

My 89Z did the same thing last year, and after following almost the same diagnostic procedure Vader suggested, (this is outlined in the factory shop manual), I found that the injector driver circuit in the computer was faulty. Since I couldn't find a value on the transistor(s) responsible for the failure, I replaced the computer for around $100. BTW, for this type of troubleshooting, at a minimum, you should get a digital Volt/Ohm Meter, a fuel pressure gage and maybe a noid light. Then you won't be replacing good parts anymore.

 

Yea, I just was confirming that the fuel regular could cause the symptoms. I realize that the shop had stated that this could be one of the problems and now that he know's this, he should start looking elsewhere.... BTW, how do you do step #3?

 

ok the temp when this first started to happen was probable
around -20 to -10 degree's, as for new parts that have been
put on since, 02 sensor, cap and rotor, plugs and wires,
the year old plugs that were in did have a bunch
of black gunk on them, i did an ignition module the horse
shoe like thing under the distributor cap, i tried a new mass
air flow sensor, chevon put on a new fuel pressure regulator
and i have since went with the new computer wich did not
change the situation besides the fact that it doesnt even
attempt to start anymore like it did before with the old
computer. I have not yet had the chance to go through
the steps that vader had mentioned and will probable
have time sunday before or after work to get in to that
thanks for the feed back and comments

 

AK,

Hopefully you didn't get charged for the replacement ECM due to their mis-diagnosis. As I said, ECMs get blamed for problems a lot more frequently than they actually have problems.

Keep us posted on your findings.

 

I'm not sure I'd trust Chevron's word of changing the FPR if they quoted him $650 to change the ECM. I wouldn't step foot in that shop again, ever!

 

I know I am adding to a super old thread here, but it helped me figure out why my 89 IROC was dumping tons of fuel into my engine causing it to flood and hydro lock. At first I thought it might be stuck injectors, but it was not. For anyone having this same issue, please check for a torn diaphragm inside the fuel pressure regulator first. There is a rubber diaphragm inside the fuel pressure regulator which can tear, allowing fuel to leak out of the regulator through it's vacuum port. This fuel will then enter your intake through the vacuum hose connection, causing the excessive fuel dump into your intake and cylinders. You can check for a torn diaphragm by doing the following. (1) - With the ignition set to the OFF position, disconnect the rubber vacuum hose that connects between the fuel pressure regulator and the upper intake. I recommend disconnecting it at the intake vacuum port. (2) - Then have someone turn the key to the ON position while you check for fuel exiting this vacuum line/hose. If fuel leaks from this vacuum line, then the rubber diaphragm inside your fuel pressure regulator has torn and needs to be replaced. The tear is allowing fuel to leak through the regulator and into your intake via the vacuum line, causing the excessive fuel dump into your engine. No fuel should flow through this vacuum line, only air. (3) - If you find that no fuel flows out of the vacuum line during this test, then your regulator is likely OK and you should follow Vador's suggestions to help you figure out the injector, electrical or ECM problem. I noticed that leaks were discussed in the threads above, but non-technical people may not fully understand what the leak was referring to, and from where, so I tried to clear it up with this additional info. Great job and appreciation to everyone that commented here, as this old thread helped me figure out an issue in 2023. Long live the Thirdgens.

 

Yep, it's an old thread, but since you added helpful info to it for some future searcher to find, I think that's cool

Your vacuum line check should of course be the first thing to check in a "fuel dumping" situation, cause the regulator is a common failure and it don't cost anything to do.

I am kinda surprised that no one earlier in the thread mentioned a Noid Light, which would have been my second check if checking the regulator found it to be OK

 

I agree. I didn't have a noid light available which would have at least ruled out stuck or faulty injector operation. I figured out the problem by chance, as I decided to remove the FPR vacuum line at the intake vacuum port, when I connected the fuel pressure gauge to the fuel rail to check fuel pressure. I didn't really need to disconnect it, but I am glad I did, because it allowed me to see fuel squirt out of the rubber hose when I hit the ignition to ON. Some folks may not be aware of the diaphragm inside the FPR, or know how it works, and may skip this check all together, which is why I decide to post my comments. Checking the FPR was not covered in much detail in the threads above and I hope our additions will help someone in the future. Take care.

 

Agreed... you'd be surprised how much old threads come in handy. TONS of useful info in a lot of them just waiting to be searched on.