4.3 CPI Stalls in gear

[randolphtpr]

what would happen if you left the fuel pressure gauge hooked up and observed what the pressure did when the engine was running and shifted...i would say from your results the fuel pressure and delivery is well within the limits to function....just a shot in the dark but there must be some kind of neutral saftey switch...it could be part of the shifting and key business in the column...i have to know what this is...please keep posting

[old_master]

No problem leaving it connected to watch as a reference only. GM does not publish any specification for fuel pressure while the engine is running.

[randolphtpr]

do you have these vac lines...check out this link for tranny vac lines...does vac check out???
i'm still thinking on this one....any news????


http://www.automotiveforums.com/vbul...ghlight=vacuum

[Sinful7]

Well, I've still been wrestling with this problem, I have yet to pinpoint an answer. Thus far, I've replaced just about everything on the top end, save for an additional spider replacement.. The conditions just aren't indicative of spider failure.

I'm wondering now, how does the engine know to increase RPM to compensate for additional load when the transmission is put in gear?

[old_master]

The ECM receives a signal from the neutral safety switch when you shift in or out of park/neutral. The ECM increases or decreases RPM as necessary. Same with the AC compressor when you turn on/off the AC or defrost.

[Sinful7]

Through the diagnosis I initially performed, aided by the FSM, I primarily considered the PN switch to be the culprit. I think I'll start tearing into that bad boy tomorrow. Is that located in the steering column?

(Posted from my Blackberry)

[old_master]

It's mounted on the transmission, the shift linkage goes through it.

[s10manic]

i might also recommend that you check the MAF Sensor if you havent already

[Sinful7]

Originally Posted by s10manic

i might also recommend that you check the MAF Sensor if you havent already

Thanks for the suggestion. It's actually a MAP sensor, and I've checked it.

[Sinful7]

Originally Posted by old_master

It's mounted on the transmission, the shift linkage goes through it.

The only P/N Safety switch I can find in the FSM is located on the steering column. Is there another thing I should be looking for? This is a 4.3CPI with a 4L60.

[old_master]

If you're using a FSM, (GM factory shop manual) for the correct year vehicle, it will tell you exactly where it is. If you're using a Chilton or Haynes repair manual, there's no telling what they say, they're just about worthless. If it's not on the transmission where the shift linkage attaches, it's probably on the steering column.

[bearcat58]

Did you ever get this problem resolved? I have the same problem with an older chevy.

[Sinful7]

Nope, still hitting it. I was studying a wiring diagram for the P/N switch and discovered that when it's closed (in P or N), it supplies a ground to the rear gate glass. The glass will not operate in any gear or reverse, so the switch itself is functioning. Now I'm suspecting the culprit is either a seperated wire to the ECM or a bad ECM. I've had to replace it (the ECM) once before, so I kinda hope that's not it.

[Sinful7]

Not to bring random dead threads back to life, but it's been three years and I'm finally getting back around to digging at this problem.

After a rebuild from the long block up, I'm certain that there's no leaks and everything is running correctly (except the idle).

So far, I've done-
(2) Knock sensors
Coolant temperature sensor
Ignition control module
Fuel filter
Fuel pressure test - 60PSI on, drops to 58 PSI when idling in park. Leakdown- pressure drops to 52 PSI after 30 minutes.
Electronic Spark Timing (ICM) test

Along with the mechanical-
Upper plenum gasket
Lower intake gaskets
Rocker cover gaskets
PCV
Crankcase breather filter
Hand cleaned UIM, LIM, heads
E-Fan Conversion

It started right back up and ran rough for a day, then I think the ECM regained consciousness and the idle characteristics evened out.

So, it's back to starting and idling fine in Park, but it dies in gear when the engine is warm.

-If I unplug the 'bypass' wire for the electronic spark timing, the engine idles in gear, just like it should... Does that perhaps indicate a bad distributor pickup or ECM?

I may just hobble this thing down to my nearest GM indy shop... three years and $100's in replaced parts to no avail- I just hate the thought that this CPI POS beat me...

[Sinful7]

Originally Posted by Sinful7

-If I unplug the 'bypass' wire for the electronic spark timing, the engine idles in gear, just like it should... Does that perhaps indicate a bad distributor pickup or ECM?

Well, it's not the pickup coil.

I unplugged the MAP sensor and re-plugged it, and the engine will crank and start, but won't hold. Now I'm beginning to suspect a fuel issue... argh. I'm taking this thing to a shop Monday for a bit o' diagnosis... heck, it's only been three years... think of all the money I've saved not driving it during that time! :-)

I'll be sure to post whatever the problem ends up being. This has been a total 'ghost' problem - all the sensors and controls check out, all of everything is functioning fine, even fuel pressure. Hopefully what I learn can be googled by others after me.