1997 Lumina no start

[amanaman1]

Hi folks...new to the forum.

Got a 97 Lumina 3.1 that cranks but won't start.

Battery is new and I replaced the ignition coils, ignition module, spark plugs and wires since there was a bit of corrosion. Still no start. I have spark, I have fuel (43 psi at the rail). Checked the crank sensor and it reads within specs ( 850 ohms and between .4 - .5 vac when cranking).

It cranks, but won't even sputter. Only time it even came close to sputtering was when I shot starting fluid directly into the intake and she sputtered and backfired once or twice. Plugs are getting wet with fuel but she just won't start.

OBD code of PO442 (small evap leak) has been there a while but car always ran fine. Now since it won't start, now have a PO141 (O2 heater) but that won't prevent it from starting. Thought maybe it jumped timing so was advised to do a compression test. Did that:

2= 160
4= 165
6= 175
1= 175
3= 105
5= 170

Did each one twice to be sure. Obviously the #3 has an issue but I don't know what is a "good" compression pressure for this engine anyway to determine if the timing has jumped. Also, the #3 could mean a valve or seal issue but I would think it would still start or at least try to. Any thoughts or suggestions you have are appreciated. Thanks!

[bszopi]

Welcome.

The numbers (besides #3) are good for compression. They are also within 10% of each other (again, ignoring 3). Which crank sensor did you check, and where did you get those values to prove that it is good? Also, how have you verified spark?

[amanaman1]

I checked the 7x crank sensor at the two wire plug at the ignition module. The values came from a GM service manual PDF page I found stating the resistance should be between 800-1200 ohms. The same GM page says the voltage should be around 2 volts when cranking but I read elsewhere that it only needs to be .3 at a minimum. Is that incorrect? I'm getting almost .5

I have two different gap type spark testers that both indicate the spark. I wasn't getting much of spark at first (would barely jump 1/4" ) which is why I replaced the coils and module. Now it sparks much better. It does seem to be gettting fuel (43psi at the rail) into the cylinders as the plugs are wet with fuel when remove them after cranking.

Maybe I am wrong but I thought the 7x crank sensor had to be working in order for it to allow the spark? What about the cam position sensor? Does that affect the spark as well or just the injectors? Someone also mentioned the coolant temp sensor and the 24x crank sensor but I don't know if either of those would prevent a start. Like I said, it is sparking so that confuses me.

Sorry to just throw all this out there but I am just trying to learn as much as I can so I know what it is I am looking for. I appreciate your input.

Thanks so much.

[86FieroSEv6]

Check the TPS voltage, key on engine off.

[amanaman1]

Well....even though the crank pos sensor checked ok according to the service info I had, I went ahead and replaced it just to ease my mind and the damn thing started right up. Thanks for the help anyways though, I appreciate it.

By the way, what a friggen pain that was to change. How is it normally done? I removed the ignition module and laid across the engine like a playboy centerfold and reached down and around the exhaust by feel. Of course it was stuck and took an hour to get out but did it all by feel but crap there's got to be an easier way.

Also, if the crank sensor was bad (which it obviously was), why was I still getting a spark? I didn't think the ignition module would fire the coils if it didn't see the crank voltage? Maybe I'm wrong. Anyway the spark I am getting now is way hotter and brighter than what I had before when it wouldn't start.

[86FieroSEv6]

A weak/intermittant signal will "confuse" the spark timing because it is effectively switching the module on and off at odd times relative to it's programmed firing order which is trying to occur each time it is "switched on".

[amanaman1]

I got it. So just because I had the close to the right "ohmage" and voltage across the sensor won't tell the whole story. That makes it hard to diagnose since I was still getting a spark, albeit not correctly. I hate to play parts changer but in this case it worked! Well....after I replaced the module, coils, plugs and wires.

Thanks again.

[86FieroSEv6]

we serve the machine masters.....