87 Cranks, but no start!

[sdhd97]

My 87 cranks hard but won't start. I plugged my scanner in and I got a code #46. I do have the GM electrical book and the shop manual as well. The Vats decoder module seems to be bad, but I would like your opinion. I found a new Delco one for $75.00.

[c4c5specialist]

HI there,
If your engine is cranking, your VATS is not the problem.
The first thing to do is to check the resistance of each fuel injector, 16.5 ohms is what you should have.
Next, check for spark, making sure its white and very bright.
Allthebest, c4c5

[sdhd97]

Thanks for the response. I have a couple of questions from reading the electronic service manual. Why would code 46 appear and in following this code to my sysmptom table, it point out the VATS control module, stating there's no command to pulse the injectors. I have had the injectors on my wish list to change out, but I have an accel super ram intake and manifold so getting at the injectors would mean dis-assembling the manifold to get at the injectors or is there another way to read the ohms?

[sdhd97]

Spark is very bright haven't checked resistance on the injectors yet, I had previously inquired with you on the best way to check them since I have never done that before. Any advice would be greatly appreciated. I turn my own wrenches and this has been a definite learning experience going from all carberated to all computer. HAL seems to be in control of my vette.....

[aquaholic]

you dont say what spark tester that has been used. if it's the in line spark plug wire type or the pencil type that rest on the wire then either could possibly show spark when there is very little. i've seen both of those show spark alot of times when there is almost none. the key is that the light on either tester should light brightly. if you used either one of those, test them on a working car first to see what a good bright spark light should look like then evaluate yours.

[sdhd97]

Spark looks good, I have a MSD all billet distributor that was refreshed a year ago and I just tuned the car up a month ago (new cap, rotor, plugs, wires).

Thanks for the reply

[bradfordsvettes]

you need a fuel pressure test and like c4c5 stated check the resistance of the injectors 1 bad one will take it down or a few borderline injectors out of spec will do the same or if it does start it will run horrible Steve

[c4c5specialist]

I have a couple of questions from reading the electronic service manual. Why would code 46 appear and in following this code to my sysmptom table, it point out the VATS control module, stating there's no command to pulse the injectors.


HI there,
Page 8a-133-8 is the wiring diagram for the VATS system in the GM electrical diagnosis supplement.
You can see the starter enable relayto the left and the ECM cranking fuel enable circuit to the upper right.
If the VATS code is correct, it allows BOTH at the exact same time.
That being said, this is why I have explained that your looking at the system not being functional.
However, if someone BYPASSED the VATS, then there is a larger problem.
Allthebest, c4c5

[sdhd97]

Thnaks C4C5, the VATS has not been bypassed, the only thing I haven't done yet is the injector ohm test. I need the easiest way you can explain on how to, for this test. Also listening to what you said about VATS not shutting a running car down, the car was idleing nice in the driveway and then it just sounded like someone just pulled the plug on her. Two hours later she started back up and I pulled her back in the garage. Since then she will not turn over just crank, with good oil pressure, strong fuel pressure, good bright spark. Could it be the ECM. She has 90,000 on her. The guy at my local GM dealership parts counter says 9 times out of ten it's the lock cylinder. Would you entertain this and is there any test for it. I hate to just buy parts.

Thanks

[c4c5specialist]

HI there,
Once again, if it was the VATS, you would not be able to CRANK the engine.
You are going to have to get to the injectors.
You will unplug them and use your digital mulitimeter to test the resistance between the 2 pins of the injector connection.
16.5 ohms is your specification.
Now, considering you have a tunnel ram, I would suggest the following.
If you reference page 8-20-6, this is your wiring for your fuel injectors.
Now, if you want to, you can resistance check each bank from the fuse location to the ECM circuit, behind the dash.
Simply apply your red lead to INJ1 or INJ2 fuse on the injector side, NOT THE POWER SIDE!!! This is done by removing the fuse and then testing for voltage. Which ever pin HAD voltage, tape off so you dont test it.
Then, remove the negative battery cable.
Once that is accomplished, you disconnect the ECM connectors. C1, pins D15 and D16 are your grounding circuits to the ECM.
So, you simply attach your red lead to INJ1 at the fuse block and D15, record your results.
Then, INJ2 at the fuse block and D16, record your results.
NOW REMEMBER, you are testing your 4 injectors for each bank, YOUR READINGS ARE NOT ACTUAL. You must multiply by 4 to get your reading. So, if you had a reading of 4.1 ohms, you would multiply that by 4, giving you your average resistance of each injector.
If ANY of this is unclear, ask further information.
Allthebest, c4c5