Es_91rs

Hey guys. My 91 rs 305tbi randomly died on me Friday and I'm a bit confused. I changed the fuel filter and verified that I have fuel at the throttle boddy, which I do. How do I test to make sure the ecm is firing the injectors and what would causethis to happen? I had someone else try to crank the car but the injectors aren't firing any fuel. I know this could also be the fpr but how should I test everything from here? As a side note, it could be me, but it feels like the gas pedal is a good bit easier to press after the car stalled but again that could just be me.

Thanks for the help guys.

aliceempire

iTrader: (14)

I'd start with finding out if the injectors are being told to fire. You can get a device called a noid light that goes into the injector connector and blinks when to crank the engine. Or you can use a test light and do the same thing with a helper to crank the key. Power should be there when ever the key is on and the ecm provides the ground when it wants the injector to fire. If it doesn't blink you need to find out if it's the power or the ground that the injectors aren't getting.

Es_91rs

Alright weather permitting I'll throw the test light on it and check them this afternoon. Almost rather hope it's a throttle body issue than a wiring issue.

cardo0

Check your fuel pressure. Many auto parts store lend these fuel press gauges out. U want to observe fuel pressure w/engine running and watch it for some time after s/d to see if it bleeds down. A good fuel sys will hold press for hours. Sorry i dont know what the TPI norm fuel presss should be and u will have to look that up. Low fuel press will be either fuel pump, regulator, blocked fuel filter or leaking fuel lines. I wouldnt bother with the TB as i dont see how this could stall the car. Bad TPS maybe but u can test that w/a voltmeter.

I always look back to the last item i worked on when a new problem shows up. Did u get this new problem just after u replaced the FF? Or was this a problem before changing the FF and FF just part of troubleshooting?

BTW troubleshooting by replacing parts is very expensive. Learn to diagnose and use the diagnostic tools.

aliceempire

iTrader: (14)

He's working with tbi not tpi. There is no Schrader valve to test pressure easily. Though it does need approximately 12 psi.

Es_91rs

This is a TBI not a TPI so there is no schrader valve to check pressure, I would have to pipe on in line, but currently there is pressure to the TB and nothing coming out of the injectors meaning it won't start. I changed the fuel filter #1 because I could still hear the pump prime even though there was no fuel coming from the injectors and #2 because that is the only thing in line between the pump and TB and it's about a year old so I needed to change it anyway.

I know that diagnostics comes before replacing parts, I am merely asking for tests that can be run to help pinpoint the exact issue before just rebuilding the TB.

cardo0

Ooops, must'a looked at the wrong profile.

Es_91rs

Ok so I just tested and my injectors are not receiving ground. They have power though. Why would the ecm stop applying ground to fire the injectors?

Es_91rs

Just checked the ecm by swapping it with my known good stock ecm and still the injectors don't pulse. All grounds to the motor seem good. Everything else appears to work. Noticed that my tach bottoms out when I try to start it and doesn't bounce or anything. Could that wire to the tach have broken because my of my air cleaner rubbing it or something? Could that cause the ecm to cut the signal to the injectors?

aliceempire

iTrader: (14)

The wire that the tach uses is just the negative side of the coil. If the coil is not being told to function then no tach. The coil and injectors(through the ecm) are referring to the distributor to tell them to act. Do you have spark? Maybe a distributor problem.

Es_91rs

I do have spark. I checked that the old fashioned way by letting the tb sip gas out of a cup and it ran perfectly fine till the cup ran out. Don't remember if the tach was working or not though.

bigal55

iTrader: (1)

Yes and yes. The ECM needs to see signal from the distributor to verify the engine is cranking/running and then will fire the injectors to supply fuel. Car cranks so probably not a VATS problem as the ECM would disable the starter relay along with the injectors. Probably looking at an ICM problem or wire as you stated. Even if the wiring is good, get that wire away from the air cleaner and secure it down to prevent future problems. You can maybe get your ICM tested at a local parts store but they can test good and still not work properly. I would inspect the wire first then have the ICM tested. If you do purchase a new ICM, don't skimp here, get a good quality unit and be sure to use heat sink compound. GL!

Es_91rs

Well the ICM is just over a month old and I would believe that would be good since it shows no signs of failure and the car never stumbled like a failing ICM usually does. I will have to get a pigtail for that side of the coil and go from there then... fingers crossed that that's all it is.

aliceempire

iTrader: (14)

incase you don't have a wiring diagram.....http://austinthirdgen.org/mkportal/m...ine_wiring.gif