96 jimmy wont start

[washbb]

I am working on a 96 jimmy with a 4.3 motor have a no start problem. seems to only start when battery is fully charged. Has new battery , ignition has plenty of spark . I checked the pressure and had 60 psi on the gauge but the gauge was leaking prety good and woudl not hold pressure so I am going to re-check with a good gauge. It seems to kick back like it is tryin gto start when you let off the key but otherwise just cranks and cranks if the Batt voltage is below 13 volts. Are ther any sensors I should be looking at for this ?

[old_master]

Is the Service Engine Soon light on when the engine runs? From the symptoms you describe, the module would be a good place to start. Most auto parts stores can check it for you at no charge. Post your results and we can help diagnose the problem, don't just throw parts at it. The results of your fuel pressure and leakdown test would be very helpful too.

[washbb]

Are you thinking the ignition module? It has good spark. what has me most curious is why it acts like it wants to start when you let off the key, kind of like an old mopar with a bad ballast resister.

[old_master]

Exactly... the module has a bypass circuit built into it. It could also be a problem with the ignition switch or a problem with the injectors not firing while cranking. It's easiest to check the module first and it's free!

[washbb]

Will get that checked then and make sure my fuel pressure is not leaking down. It only uses two injectors am wondering if I can use a test light to see if they are getting pulsed. I have read that the ignition switches can be problems too and was thinking that would be my next thing to change if I was just going to throw a part. It has 220k on it and the fuel pump was replaced once about 3 years ago.

[old_master]

1996 has CSFI controlled by OBDII and uses 6 mini injectors, should look very similar to this:




.... unless it's been changed to CMFI, (uses 2 injectors) through a TSB. DO NOT use a test light unless it is digital.

[washbb]

That sure looks like it. The part behind the throttle body must be the regulator then. Injectors are not on a fuel rail like a standard V8 very different set up am going to re-read the hanes on it.

[old_master]

The fuel pressure regulator is inside the plenum. The electrical plug on top of the plenum is for the injectors. Don't rely on Haynes for anything more than the very basic stuff, like oil changes Most of their information is either incorrect, incomplete, or totally missing.

[washbb]

Just spent some time working on the jimmy again with the following results. Fuel pressure is at 60-63 lbs with key on. Ignition module checks good and have spark to the plugs. Would not start so I charged the battery fully again to about 14 volts when I removed the charger. It started right up with no problems, added a can of sea foam just for good measure and drove about 30 miles and probably idled it around an hour. Started 6 times in a row so quit for the day. I also checked at the starter to see if I was getting full voltage and it is within a tenth of a volt both static and cranking was at 12.4 volts before I put on the charger. When I first tried to start it It cranks and then it slows down like the plugs are firing at wrong time when you let off the key you get a kick back like it's firing also. Am running out of ideas short of taking it in for a complete scan while it's still running. I get no codes at all when I check with my reader. Am thinking i have a problem with wiring or a sensor or pcm that does not show up when battery is at maximum charge.