testing for pulse voltage to the injectors
Thread Starter
8th Gear
Joined: Oct 2011
Posts: 8
Likes: 0
testing for pulse voltage to the injectors
Is there a way to check for pulse voltage from the ecu TO the injectors? Can I stab the inj. wires with a 12v continuity light to BE SURE the problem lays with the ecu and NOT the injectors? My 1989 has had new injectors installed about 2k ago,allong with a new fuel/air filter/egr/plugs/cap/rotor/wires. Overnight, it now just cranks but will not fire. A shot of ether will let it run for seconds. Sometimes while cranking the stater motor will just stop. HAd it & the battery checked out, both good. H E L P !!
Le Mans Master
Joined: Oct 2006
Posts: 6,842
Likes: 285
From: Palmdale CA
Look up 'noid light' and you'll have your answer. You can't just plug in a DVM and get a result. There is an ohm reading for resistance of the coils, but as far as injector pulse, you'll need a 'noid light'. You can get a test set from Harbor Freight.
Finally, if you're doing the kind of things you're doing to your Vette', by all means, you should have a FSM or Factory Service Manual. You should also be looking at what, if any codes are thrown by the ECM. Go to the C4 tech forum and do a search on the problems on your 89'. Early C4's are notorious for starting, ignition and fuel problems. They are complex and you have to go step-by-step in figuring it out.
Finally, if you're doing the kind of things you're doing to your Vette', by all means, you should have a FSM or Factory Service Manual. You should also be looking at what, if any codes are thrown by the ECM. Go to the C4 tech forum and do a search on the problems on your 89'. Early C4's are notorious for starting, ignition and fuel problems. They are complex and you have to go step-by-step in figuring it out.
Thread Starter
8th Gear
Joined: Oct 2011
Posts: 8
Likes: 0
89 start problems
Thread Starter
8th Gear
Joined: Oct 2011
Posts: 8
Likes: 0
89 no start
Look up 'noid light' and you'll have your answer. You can't just plug in a DVM and get a result. There is an ohm reading for resistance of the coils, but as far as injector pulse, you'll need a 'noid light'. You can get a test set from Harbor Freight.
Finally, if you're doing the kind of things you're doing to your Vette', by all means, you should have a FSM or Factory Service Manual. You should also be looking at what, if any codes are thrown by the ECM. Go to the C4 tech forum and do a search on the problems on your 89'. Early C4's are notorious for starting, ignition and fuel problems. They are complex and you have to go step-by-step in figuring it out.
Finally, if you're doing the kind of things you're doing to your Vette', by all means, you should have a FSM or Factory Service Manual. You should also be looking at what, if any codes are thrown by the ECM. Go to the C4 tech forum and do a search on the problems on your 89'. Early C4's are notorious for starting, ignition and fuel problems. They are complex and you have to go step-by-step in figuring it out.
I WAS lucky enough to pick-up a FSM & Haynes on e-bay & it arrived yesterday
Would the TEMP sender in front of the motor have a effect on what the ecu tells the injectors?
On another note, is there an EASIER way to get at the ecu other than inverting ones self in the passenger seat and try to axcess the mounting bolts to it? The "bread-box" is next to impossible to get out of the way unless the ENTIRE dash pad is removed. No wonder they moved it into the engine compartment for the following years!
Le Mans Master
Joined: Oct 2006
Posts: 6,842
Likes: 285
From: Palmdale CA
The ECU is almost always the last thing that goes bad. What inputs it recieves from the various sensors is far more likely. Have you seen what codes it's thrown yet? Are you familiar with how to retrieve the codes from your car? It's pretty easy. You just jump the connector under the dash with a paperclip. One end goes to "A", the other to "G" and then you turn the ignition to run (don't start the car). You should get an immediate 'flashing' of the SES or Service Engine Soon light. The first three sets of flashes are the "Hello", then it will start to flash the codes three times each. Three flashes an interval and then Six flashes is Code 36. This will repeat two more times and then it will go on to the next 'set' (it's been awhile, so anybody, feel free to jump in to correct me!
Thread Starter
8th Gear
Joined: Oct 2011
Posts: 8
Likes: 0
89 no start
The ECU is almost always the last thing that goes bad. What inputs it recieves from the various sensors is far more likely. Have you seen what codes it's thrown yet? Are you familiar with how to retrieve the codes from your car? It's pretty easy. You just jump the connector under the dash with a paperclip. One end goes to "A", the other to "G" and then you turn the ignition to run (don't start the car). You should get an immediate 'flashing' of the SES or Service Engine Soon light. The first three sets of flashes are the "Hello", then it will start to flash the codes three times each. Three flashes an interval and then Six flashes is Code 36. This will repeat two more times and then it will go on to the next 'set' (it's been awhile, so anybody, feel free to jump in to correct me!
THAT'S the problem...all I'm getting is the 12 code showing the computer is working....NO other trouble codes AT ALL!
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Race Director
Joined: Jun 2004
Posts: 13,939
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From: WI
When I needed to check that I went super simple and just plugged a light bulb in the injector socket. A spare from the digi dash worked very well.
The computer is really easy to get down, I thought. Remove the hush panel, use a mirror to look up while sitting along side the car. Then with a long extension undo the two 10mm bolts. The computer drops down.
I had a reoccurring bad o2 code once. Replacing the sensor did not help. I followed the FSM chart and found the circuit good. Then followed the chart for bad ECU. I did not get the bad ECU code but that was indeed what the problem was. Replaced the ECU and it was fixed. I made a thread on it awhile back.
The computer is really easy to get down, I thought. Remove the hush panel, use a mirror to look up while sitting along side the car. Then with a long extension undo the two 10mm bolts. The computer drops down.
I had a reoccurring bad o2 code once. Replacing the sensor did not help. I followed the FSM chart and found the circuit good. Then followed the chart for bad ECU. I did not get the bad ECU code but that was indeed what the problem was. Replaced the ECU and it was fixed. I made a thread on it awhile back.
Thread Starter
8th Gear
Joined: Oct 2011
Posts: 8
Likes: 0
When I needed to check that I went super simple and just plugged a light bulb in the injector socket. A spare from the digi dash worked very well.
The computer is really easy to get down, I thought. Remove the hush panel, use a mirror to look up while sitting along side the car. Then with a long extension undo the two 10mm bolts. The computer drops down.
I had a reoccurring bad o2 code once. Replacing the sensor did not help. I followed the FSM chart and found the circuit good. Then followed the chart for bad ECU. I did not get the bad ECU code but that was indeed what the problem was. Replaced the ECU and it was fixed. I made a thread on it awhile back.
The computer is really easy to get down, I thought. Remove the hush panel, use a mirror to look up while sitting along side the car. Then with a long extension undo the two 10mm bolts. The computer drops down.
I had a reoccurring bad o2 code once. Replacing the sensor did not help. I followed the FSM chart and found the circuit good. Then followed the chart for bad ECU. I did not get the bad ECU code but that was indeed what the problem was. Replaced the ECU and it was fixed. I made a thread on it awhile back.
Thread Starter
8th Gear
Joined: Oct 2011
Posts: 8
Likes: 0
