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Amedee
Amedee, Cadillac Technician
Category: Cadillac
Satisfied Customers: 24801
Experience:  ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
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It cranks, has fuel to the injectors, will run when starter

Customer Question

It cranks, has fuel to the injectors, will run when starter spray is applies so it has spark. There is voltage to the injector. Will only run until the starter spray is exhausted
JA: Tell me a bit more about what's going on so he can help you best.
Customer: I just did, what specifically did I not tell you?
JA: Are you hoping to fix this yourself?
Customer: YES
JA: Great! What have you tried so far?
Customer: It has a new fuel pump, new fuel pressure regulator. It has fuel pressure. and spark. It doesn't seem that the injectors are firing...though I don't know, I'm open to trying anything
JA: Is there anything else important you think the Cadillac Mechanic should know about your Cadillac?
Customer: Its a 1990 Cadillac Allante 4.5, 175k miles up until it just stopped running suddenly without warning it ran GREAT. Had just driven it about 40 miles, parked the car and came back to it about an hour later and it would not start. No warning of any kind
JA: I'm sending you to a secure page on JustAnswer so you can place the $5 fully refundable deposit now. While you're filling out that form, I'll tell the Cadillac Mechanic about your situation and connect you two.
Submitted: 9 months ago.
Category: Cadillac
Expert:  Amedee replied 9 months ago.

Hello and welcome! My name is ***** ***** I can assist you with your question. Are you saying that the injectors are not getting pulsed to open fuel into the cylinders? Can I start by getting your VIN? Thank you!

Customer: replied 9 months ago.
That it what it appears. There is voltage to one lead of the injector, when the ignition switch is on. I don't know if it is pulsing. It has gas flow to the injector rail. VIN: 1G6VS3383LU127182
Expert:  Amedee replied 9 months ago.

Hello! Are you able to check injector pulse using a noid light?

Customer: replied 9 months ago.
No, I did not check with a noid light. I just checked the supply power to see if it was hot. Which it was. I do not have a noid light, however, if that is the next step, maybe I should get a set.
Expert:  Amedee replied 9 months ago.

I suspect there is no pulse from the computer.. but I would just want to verify this. Does the engine have spark and fuel pressure when cranking?

Customer: replied 9 months ago.
it has spark. If you spray starter fluid into the air filter intake, it will start and run until it has exhausted the fuel supply from the spray. It has good fuel pressure to the injector rail. When the ignition is on, it will spray gas if not connected. The fuel pump is new as is the fuel pressure regulator
Expert:  Amedee replied 9 months ago.

Ok, does the check engine light come on with the key on? Does the Throttle position sensor have a 5 volt reference going to it with the key on?

Customer: replied 9 months ago.
The check engine light is always on, so that isn't an indicator of this problem. Ill have to check the voltage at the throttle position sensor, Ill let you know...stay tuned
Expert:  Amedee replied 9 months ago.

That sounds good. As long as there are no security issues going on preventing the injectors from firing and the TPS is in fact getting a good reference voltage, you could have a bad TPS or even a bad PCM/computer. Were either of those replaced as of yet?

Customer: replied 9 months ago.
No, the PCM computer has not been replaced. and there have been no issues with the security system that I know of. However, if that were the case, would it still be getting spark to run with the starting fluid? All other systems seem to be working with the exception of the fuel delivery at the injectors. TPS? I'm not familiar with that abbreviation. What is the TPS?
Expert:  Amedee replied 9 months ago.

The TPS is the throttle position sensor. The PCM needs to see a correct signal from the TPS in order to pulse the fuel injectors.

Expert:  Amedee replied 9 months ago.

Its been a while since I have worked on this old of a cadillac, so if memory servs me correct, the security system shuts off the injectors or it cuts power to the starter. Either way, if it is a security issue, there should be a security light on or flashing on the dash with the key on or when trying to start the engine.

Customer: replied 9 months ago.
Thanks. There is no indication of security failure. No indicator lights or any other issue. I have had past issues with the security and then it cut the power to the starter. Not to say it doesn't cut the injector flow as well. Just no indication. I need to do the trouble shooting on the throttle sensor and get back to you.
Customer: replied 9 months ago.
Ok, I know it qualifies as an antique. So hopefully you can dust off the remote corners of you memory. Yes, dinosaurs roamed the Earth when it was new....
Expert:  Amedee replied 9 months ago.

Good morning and sorry for the delay! I did some research for you and found out the security system prevents power to the starter motor. Since your engine is cranking over, the security system is not going to be an issue.

Expert:  Amedee replied 9 months ago.

It sounds to me like this is going to be related to the TPS or the computer. Also be sure to check the MAP or MAF sensor (which ever this vehicle has) as this can affect injector pulse as well.

Expert:  Amedee replied 9 months ago.

I do work all day today and will not get homt until late this evening. Please post your results/findings on this page and I will reply back tonight after work. Good luck and have a great day!

Customer: replied 9 months ago.
Ok, now I'm totally lost. Checked power to the TPS. Of the three leads the power input is 5.6v. I got a noid light and plugged it into one injector and did get a pulse. It has fuel at the injector rail. It still does not start. Turns over fine, not firing at all.
Expert:  Amedee replied 9 months ago.

Are the injectors spraying fuel while cranking?

Expert:  Amedee replied 9 months ago.

If so, you might just have bad gas. IF not, the fuel injectors might just be bad/clogged

Customer: replied 9 months ago.
I just confirmed that I have spark to the plugs. So all lights pulsing. Injector test light and the plug test light. I had a loose connection for the fuel inlet to the injector rail and gas was spraying out until I tightened it. It has a few gallons of fresh gas....or so its supposed to be. So now it looks like bad gas?
Customer: replied 9 months ago.
When I push the vent valve on the pressure regulator, no gas comes out, though I didn't test that with the engine turning over. Just with it stationary. Don't know if that is an indicator of anything
Customer: replied 9 months ago.
with everything seemingly having power as shown with the test lights, the TPS is good I can assume?
Customer: replied 9 months ago.
Would all the injectors be bad/clogged at once?
Expert:  Amedee replied 9 months ago.

Thats correct. It sounds like everything is working normal. If fuel is being pulsed from the injectors into the engine while cranking, it sure sounds like bad gas. No, the injectors do not all plug up and once.. unless one of them shorts out pulling the rest down.. electronically. But if you have pulse, it should not be an issue/

Customer: replied 9 months ago.
I didn't check all the injectors, just one
Customer: replied 9 months ago.
Should I check all of them?
Expert:  Amedee replied 9 months ago.

I would just to be sure..

Customer: replied 9 months ago.
ok. Ill let you know the verdict...stay tuned...
Expert:  Amedee replied 9 months ago.

Sound good! Have a great night!

Customer: replied 9 months ago.
Fyi...I didn't check them all as it was a real pain to get them off and after checking three it seemed very unlikely that any of them would be bad. And even more unlikely would be that all of the injectors would fail at exactly the same time and the exact same way. In which case it would run but very erratic and very badly. I even took the injector rail loose to see if it was indeed getting gas into the rail, which it was. It seems now the only common denominator that would have such a global effect would be the gas....that is very weird but what else?
Expert:  Amedee replied 9 months ago.

Hello and good morning! Bad gas sounds like the only possible cause at this point. I work again all day today but will be back online tonight.

Customer: replied 9 months ago.
It still is not starting. I have been checking the gas and I don't think it is possible for the gas to be bad. Even if it were bad, which I'm almost certain it isn't, it would at least try to run. You could run kerosene through it and it would at least fire. The problem is definitely fuel distribution related, as it will run when starter spray is used. Do you know what the fuel pressure should be at the injector rail> Maybe the pressure is low?
Expert:  Amedee replied 9 months ago.

YES, I can look it up. How much fuel pressure do you have?