TBI injectors not firing

1988 CHEVROLET 3500
48,000 MILES • 7.4L • V8 • 2WD • AUTOMATIC
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PHILL WATERS
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We had the vehicle shut down and would not start due to fuel filter being blocked. replaced the filter and rebuilt the TBI but it would now start but would not run without continually pumping the gas pedal. checked fuel pressure found it was down so replaced the fuel pump. But now there is no fuel coming from the injectors vehicle will start and run while spraying fuel down the TBI. Have had it suggested that it might be a fault in the ECM. so how do I check this or what else am I missing?

Cheers,
Phill
May 20, 2019 at 11:08 PM
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ASEMASTER6371
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Good morning,

You need to use a noid light on the injectors to see if the ECM is commanding them on. You can rent one at a parts store.

What is the fuel pressure with the new pump?

Roy
May 21, 2019 at 2:37 AM
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PHILL WATERS
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Hi Roy, as I live in Australia to rent a noid light isn't possible I can purchase a kit with 10 different noid lights in it for $35.00 of eBay but do really want to do that is there another way to test them? I can see that they are not spraying any fuel out. Also the fuel pressure is about 10 psi.
May 21, 2019 at 2:59 AM
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ASEMASTER6371
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Okay, got it.

Use a test light and insert it in both terminals. Crank the engine and see if it flashes.

Roy
May 21, 2019 at 3:05 AM
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PHILL WATERS
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Okay will have to do this in the morning as it is night time over here at the moment will let you know outcome.

Just a little bit more information after fitting the new fuel pump we started the engine but would not run without pumping gas pedal both injectors were spraying fuel but have since stopped and when cranking engine over they are completely dry.
Cheers
May 21, 2019 at 3:13 AM
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ASEMASTER6371
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Make sure the new pump is working. You said 10 lbs. Is that on the new one?

Roy
May 21, 2019 at 3:15 AM
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PHILL WATERS
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Pump working can hear it plus disconnected inlet line on TBI and turned on ignition and had a steady flow of fuel flowing from the line. So know that pump is working.
May 21, 2019 at 3:19 AM
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ASEMASTER6371
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Okay, do the test on the injectors.

It does sound like the quad drivers in the ECM failed.

Roy
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May 21, 2019 at 3:35 AM
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PHILL WATERS
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Hi Roy , did as you suggested and put a test light on the lead to the injectors and cranked the engine over but did not get anything. so is it the drivers and will I have to replace the whole unit or is there something else that may need investigating?
Cheers,
Phill
May 22, 2019 at 12:59 AM
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ASEMASTER6371
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The ECM needs to be replaced. It is the whole unit.

Roy

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May 22, 2019 at 2:59 AM
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PHILL WATERS
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Hi Roy,
managed to find someone who had a noid light not the correct one but with the use of alligator clips etc., managed to jury rig a working light, on first crank over light flashed once then nothing so disconnected ECM and re-plugged it back in and again got single flash on crank over then nothing. so would that be still the ECM?
May 23, 2019 at 4:10 AM
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ASEMASTER6371
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Yes that is correct.

Roy
May 23, 2019 at 4:37 AM
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PHILL WATERS
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Okay, have ordered new ECM, but it will take about 10 to 15 days to reach me. will let you know how it goes., thanks for all your help.
Cheers,
Phill
May 23, 2019 at 3:30 PM
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ASEMASTER6371
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You are welcome.

Always glad to help.

Roy
May 23, 2019 at 3:32 PM
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JAY TACKETT
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Curious to know If the ECM fixed the problem? Having similar problem myself thanks.
Dec 14, 2020 at 9:09 PM
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ASEMASTER6371
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Usually we only hear back when it does not fix it.

If you like, start a new question and we would be happy to help you.

Roy
Dec 15, 2020 at 5:21 AM