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1989 Grand prix no injector pulse
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61suburban
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Jun 4, 2008, 4:24 PM
Post #1 of 14
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1989 Grand prix no injector pulse
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I have a 1989 Grand Prix 3.1 no start condition .I have no injector pulse but voltage at the injector on both sides like it should since it is wired in parallel.The unit will run on carb cleaner .We have 40 psi fuel pressure,a crank signal, correct TPS voltage,no noid light activation.I have run down the ALLdata trouble tree as they suggest .Voltage at the mini harness,power at the module,good grounds,no back feed of voltage from the ECM.I have a 2.5 volt reference from the module to the ECM is this enough ?? Should it be 5 volts as most sensors are.Replaced the Module and the ECM no change.Anybody run into this or any ideas.
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DanD
Veteran
/ Moderator
Jun 5, 2008, 6:59 AM
Post #2 of 14
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Re: 1989 Grand prix no injector pulse
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Have you checked TPS voltage at closed throttle? A shorted to reference voltage, TPS could put the ECM into a clear flood mode and turn off injector pulse.
Should be around .5 (1/2) volt at closed throttle and 4.5 volts at wide open.
Test this at the signal return wire, at the ECM; it should be a dark blue wire at terminal 15. Not sure witch one of the two connectors; my wiring diagram doesn’t have the connectors labeled for some reason.
Why I say test it at the ECM, is that you’ll also be testing the harness as well for short to power.
Dan.
Canadian "EH"
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61suburban
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Jun 5, 2008, 4:14 PM
Post #3 of 14
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Re: 1989 Grand prix no injector pulse
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Closed throttle TPS is .68 volts and the WOT is 4.68 volts as per my scanner.I'l get back on the voltage at the ECM .Any ideas on the voltage from the module ? Do you think 2.5 volts is enough
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61suburban
User
Jun 5, 2008, 8:24 PM
Post #4 of 14
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Re: 1989 Grand prix no injector pulse
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The voltage is .6 volts closed throttle and 4.1 volts @ WOT .I tried holding at WOT with a Noid light and no signal either. Do you have pin out voltage for the ecm, alldata does not list for this year. I reallly think I have a open wire somewhere but where is the question.
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61suburban
User
Jun 6, 2008, 7:32 PM
Post #6 of 14
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Re: 1989 Grand prix no injector pulse
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The ECM connector in question with 2.5 volts is connector 430 from the module.I have not disconnected the harness under the plenum.I did check at the mini harness behind the ecm checking for voltage at conector A ,K,E,F then checked the resistance of the injector harness .How do you suggest to fire the injector ? Ground the ECM side of the injector ? And as for the antitheft I don't see one since it is so old.Unless someone added One ? I'll look at it Saturday.Thanks for the help Dan.
Eric
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DanD
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/ Moderator
Jun 7, 2008, 3:34 AM
Post #7 of 14
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Re: 1989 Grand prix no injector pulse
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I’m down at the lake for the weekend and don’t have access to my manuals to see what this circuit is. Need high speed internet and all that’s available along this section of the north shore of lake Erie is dial up. Maybe there’s a reason they call this village “Turkey Point”. LOL
Yea to fire one of the banks of injectors is too momentarily ground the driver side of the harness and I mean momentarily. I usually have a pressure gauge connected to the fuel rail; pressurize the system, fire the injector(s) and compare the pressure loss, difference between the banks.
I never thought of after market security systems; well worth a look. You never know what someone may have added too the system that has long been forgotten or never known about, by this owner of the vehicle?
Dan.
Canadian "EH"
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61suburban
User
Jun 9, 2008, 5:14 PM
Post #8 of 14
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Re: 1989 Grand prix no injector pulse
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Hey Dan the puzzle has not been solved.I pulled the upper plenum and verified voltage on circuit 639/839 all good.Checked for continuity at 467/468 all good.Checked resitance of injector .6 ohms all injectors.verified ground at D4,D10.No theft system .I did not test for injector spray due to I know I have power and continuity so what gives I'm stumped .
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DanD
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Jun 9, 2008, 6:34 PM
Post #9 of 14
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Re: 1989 Grand prix no injector pulse
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Not sure what to suggest, other then possibly one of the replacement parts were defective? It wouldn’t be the first time finding a defective module right out of the box?
Dan.
Canadian "EH"
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DanD
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Jun 10, 2008, 5:56 AM
Post #10 of 14
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Re: 1989 Grand prix no injector pulse
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This is bugging me as well; the system isn’t that complicated?
Can or have you checked for continuity of the injector circuits at terminals D9 and D3 of the ECM connector?
Disconnect the ECM, turn the ignition on, with a test light connected to ground, probe terminals D9 and D3 of the harness. The test light should light on both terminals.
If you have good spark on all three coils, that tells us the ignition module should be ok.
Does the check engine light come on with the ignition in the run position?
Have you tried jumpering terminals A&B of the ALDL and see if the check engine light will flash codes? It should always at least flash a code 12. (No codes) Are there any codes?
Most scan tools will run a diagnostic circuit check that will walk you through a test of commanding the computer to flash code 12; will yours and did the test pass?
Now don’t laugh at this one but reconnect everything other than maybe one injector, so you can attach your noide light. Place the ECM in the palm of one hand and have someone crank the engine for you. With the other hand slap the ECM, with a good firm smack; not enough to dent the case but damn near.
While you’re slapping Fred, watch the noide light or listen if there any sound of a firing of a cylinder.
Believe it or not but GM called this simulating road shock and was considered a viable test. The cold solider on the ECM boards would go open and cause intermittent running issues until the circuit would stay open and stall out the engine.
Dan.
Canadian "EH"
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61suburban
User
Jun 10, 2008, 3:01 PM
Post #11 of 14
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Re: 1989 Grand prix no injector pulse
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I did check for power at the D3,D9 with a volt meter and was fine.The check engine light is on with key on I did verify that.I will take another look at it tonight and see if I can get the ECm to flash code 12 and also I want to check the injector resistance I don't think my multimeter was reading correctly at the .6 ohms so I borrowed one from a friend.I'm not sure if my scanner will run that test but I can manually do it.
In regards the slapping trick I forgot about that one .I worked in a dealership in 1980-83 and remember doing that a few times after you mentioned it.I'll get back
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DanD
Veteran
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Jun 10, 2008, 6:56 PM
Post #12 of 14
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Re: 1989 Grand prix no injector pulse
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Check D3&9 with a test light; the test light will put a small amount of load on the system, where a 10 mega-ohm DVOM will not.
The DVOM will read whatever voltage that is on that circuit without being intrusive to that circuit. A test light requires current flow to light the light; if there’s high resistance in the circuit, a test light will not light; where a “good” voltmeter will show system voltage.
Dan.
Canadian "EH"
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61suburban
User
Jun 11, 2008, 2:40 PM
Post #13 of 14
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Re: 1989 Grand prix no injector pulse
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 Okay we be smilin now I got it figured out.I did the test with the test light and both have power at the ECM.I went again and checked my harness resistence and had 4.5 ohms spec is 4-5 ohms with injectors harness connected.I then ohmed each injector and found 1 that was .6 ohms and the rest where 11.5-12 ohms.I disconnected the injectors from the harness and installed the noid light on each connector .BOOM I got power.Checked each one on the rear bank and all flashed the light  HUM .Did the same with the front bank all flashed until I connected the injector with .6 ohms .It must be shorted out and must be grounding the common ground in the driver for the other bank.Odd the harness test didn't show a difference compard to the other bank.
So anyway I have'nt installed the injector yet may have an oppurtunity tonight or tomorrow.I really appreciate all your help and will drop in from time to time and see if I can be of any help. Eric
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DanD
Veteran
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Jun 11, 2008, 4:26 PM
Post #14 of 14
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Re: 1989 Grand prix no injector pulse
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Good stuff, let us know the end resault.
Dan.
Canadian "EH"
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