No start, no codes, I'm stumped

[alan]

Hi guys,
I normally just lurk around learning from others but now I have a problem. It's a 96 w/ LT4, 77800 miles. It turns over but will not start, and there are no codes from scanning. I pulled the connector from the MAF and it did show a 0100 code for MAF. If you let it try to start it turns over and acts like it wants to start sometimes, and sometimes sounds like a backfire thru air cleaner. I have good fuel pressure at the regulator and it does not leak down when key is turned off. I have spark at the coil, but this is as far as i got. I've been all over the FSM without any luck. I am beginning to think Opti, but would like to confirm it. !'m 60 years old and have been turning wrenchs since my first car at 12 years old (54 Chevy), and did a lot of drag racing when young. I've worked on cars boats and bikes and now don't know what to do next.
I would appreciate any input that anybody can give. It must know I was thinking of selling or trading for an automatic C4 or C5 due to bad back.
Thanks in advance,
Alan

 

[Hib Halverson]

Do you have the factory service manual?

If so, look in Section 6E for the diagnostic instructions for a cranks-but-won't-run-condition.

Performing those diagnostic procedures may lead you to a solution, but if they don't, please post the results to this thread and then, perhaps, some CAC members will post some suggested solutions.

 

[alan]

Thanks Hib. I have a FSM and was trying to work my way through the diagnostics. I will continue with 6E as I started with. I think it is pointing to the opti, but hope not.I'll check the vacuum line on the FPR. I didn't think of that.
Thanks
Alan

 

[John Robinson]

Read the section that covers the TPS. If it is bad the ecm will think the engine is flooded and wont provide fuel to the injectors. This happened to me it cost me the price of an ecm because I did not have any codes and the mechanic said it was bad. And yes if he had not found the tps bad he was going for the opti because of the rep they have.

 

[John Robinson]

I will save you the time to look up the TPS in your FSM

Hope this sheds some light on the tps for you

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Throttle Position Sensor (TPS)
Copied from 1993 Service Manual
The Throttle Position sensor (TPS) is a potentiometer connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts
from the ECM and the other to ECM ground. A third wire is connected to the ECM to measure the voltage from the TP sensor. As the throttle valve angle is changed (accelerator pedal moved), the voltage output of the TP sensor also changes. At a closed throttle position, the voltage output of the TP sensor is low (approximately .5 volt). As the throttle valve opens, the output voltage should be approximately 5 volts.

By monitoring the output voltage from the TP sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent burst of fuel from the injectors and cause an unstable idle, because the ECM detects the throttle is moving.

If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensor circuit is shorted a DTC 21 will be set. A problem in any of the TP sensor circuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use a default value for TP sensor, and some vehicle performance will return.

A personal note, when my TPS failed it DID NOT set a code other than to tell me the ECM was bad.

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[vetteoz]

I have good fuel pressure at the regulator
I have spark at the coil,

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Lt1 No Start Diagnostic - Mainstreamtopics - Your General Forum

 

[Itshakes]

"I have spark at the coil"

My '96 LT4 did the same thing! It was a bad coil wire going into the Opti. The boot on the wire was split, and shorted out on the back of the waterpump! Look closely at the wire, and twist the boots to see if they are cracked.

 

[alan]

Thanks for all the responses. I have to fit in working after work and in between the rain that is part of So Florida afternoons, but I have spark at the coil and I pulled a plug wire and have spark there. I also have a MSD 6A box and Blaster coil, and I'm thinking about disconnecting them and going back to stock. Throttle position sensor didn't throw a code bur it did light the ASR on and off on the panel which it did before when the original went bad. I replaced the sensor but didn't help.
I probaly won't get much time till the weekend to spend some serious time with all the forum answers and the FSM.
The best advise I have ever gotten was from here. Buy and use the FSM!!
Thanks,
Alan

 

[boomdriver]

no real useful advice here except to say that if you keep going thru the FSM flow charts to their conclusion you will know whats wrong...

IMHO, it smells of optispark. The opti can still produce spark, and not lite a kleenex soaked in gas. As precise as they are designed to be in operation, they can be as "off" in failure...spark at weird times, dwell thats across the BDC...everything thats opposite of precise. Many many folks get the ol spark tester out and see a nice arc and assume that all is well...and they all think someones scamming them when they have to lay out 2-$300 for a new optispark, but it runs like new again.
Strange...

Good luck

 

[alan]

Update - It runs now

First let me thank everyone that tried to help me, there was some great advice and I appreciate it.
Now I must apologize for my stupidity. I did not mention that I had a MSD 6A box and old style Blaster coil, which I'm sure someone would've me to remove and then troubleshoot the problem. Saturday morning when I started to work on it, I realized that I needed to remove MAD stuff and go back to stock. It now is stock and runs great. I have always used the Kiss method since the 60's, and when applied to this problem it still works.
Thanks again and I'm sorry to have wasted your time on a dumb problem.
Sunday was a beautiful day for a ride and I love to hear the LT4 scream thru the gears from the muffler elims.
Thanks for all the great responses. Now I can put it up for sale anf find one with auto trans that I can drive more, as the clutch really bothers my bad back.
Thanks again,
Alan

 

[John Robinson]

That's good to hear thanks for the update.