Projection Cold Stall?

[Puslinch]

Over the pass weeks my 90GW has had a problem with the first start up. Starts fine, if I leave the truck run for 5 minutes the RPM drops and stalls.
With the Projection there is a Fast Idle soleniod it seems to retract to quickley and there is no adjustment for duration. I assume that once the coolant temp rises the to a certain temp, the soleniod retracts. Then it's on it's own to run on the idle setting 800 Hot neutral, 600 Hot in gear.
But the engine isn't hot yet.

Advise?
I've checked timing, vacuum leaks, etc. The only difference is I had a new down pipe installed and the O2 sensor is closer to the cat, much closer. But the sensor shouldn't be online until it realy gets hot or is the sensor getting hot from the cat?

[JohnnyJ]

I wonder if your O2 sensor is too far back. Mine is marginally located, so I have some problems with the idle. I want to redo the exhaust to 2.5", and if I do I will have the O2 sensor mounted reallllly close to the Y-pipe. Currently, it is about 5" back from the Y; I don't have a cat from the factory, so I can't tell you how close to the cat this would be.

I ended up bumping the idle to 900rpm to make sure the sensor was getting enough exhaust to read, at 700-800 it was not enough and it would start railing the idle arm and it would stall. I talked to one of the techs at Holley and this was his suggestion, as was moving the O2 sensor closer.

My problem became much more noticeable as I drove. It would try to stall when sitting at a stop light and the system was at idle; it was the idle solenoid doing it to me.

[Veepster]

hey Johnny....are you running or a 3+ wire O2.....

I am sure there is a method to change the duration of the cold circuit...what type of sensor is it using to tell the computer when the truck is cold?......for example, my AirSensors unit uses a sensor that mounts on one of the intake bolts, if I use the center bolts(near the exhaust crossover in the intake) the cold circuit is much shorter than if I use one of the end bolts on the intake....

[SpruceMoose]

the "choke" control on the ecu controls not only how much extra fuel to give the engine while it thinks its cold, but also the point at which it switches from "cold" operation to "hot" operation. try advancing the choke control some more. also, how does it run if you disable the closed-loop module?

remember: while on the choke circuit, the closed-loop system is inop. it is running in open-loop mode, and therefore only the settings on the ecu are in use. to help in troubleshooting (and because i'm nosey) i added some LEDs to the closed-loop box:

green for power
yellow for choke mode
green/orange for auto/manual mixture mode

nice to be able to see whats going on.

good luck, and keep us posted.

sm.

[Puslinch]

I'll try the increasing the choke, thanks Moose.

[Ralph]

You might also try replacing the coolant temperature sensor.

[Puslinch]

I spoke to Holley this morning and they also mentioned the only problem could be the temp sensor. At 72f it should read 3800 ohms and at 212f it should read 182 ohms.
I'll look at that tonight.

[SpruceMoose]

puslinch: GREAT tech info! that gets filed away for future use! keep us in the loop!

sm.

[Puslinch]

Problem solved:
It was the riser valve on the exhaust manifold, the valve was seized closed. The sensor was good.

[SpruceMoose]

great! glad you figured it out. and thanx for the other info.

sm.

[Ralph]

That's excellent information, Puslinch. When you get into EFI troubleshooting you have to out-think the dang ECU.

In your case, did it turn out that the blocked heat riser valve was preventing enough hot exhaust from passing over the O2 sensor that it couldn't get up to operating temperature?

[Puslinch]

Ralph:
The o2 sensor is still way to close to the cat, I'm going to move it next weekend. In fact the sensor was installed 2" from the cat. Holley says this is a no no. My original placement was right or the joint of the Y pipe about 10" away from the cat.
The riser valve was sorta choking the engine, poor idle, acceleration and higher engine temp. If the valve is seized closed that would mean the engine heats up quicker, but this is false the right side does. The manifold was hotter than hot! Wish I had a infared temp guage.
I wired it open and the trucks runs great! BTW, you can also be to rich on the choke circuit.
Moose - where did you install the LED's on the controller? or in the Rich Lean unit?
Thank for all the advise!

[SpruceMoose]

puslinch: i installed the LEDs in the face of the closed-loop box. i have the box mounted to the underside of the steering column, with the flanges up. the original red LED for rich/lean is facing the drivers seat, and the 3 other LEDs and the manual/auto switch are all on that same face.


switch green/orange red yellow green
man/auto man/auto mix choke power

hope that makes some sense. if i ever get a camera i intend to get some pics and post them here.

sm.