Fixing TH350 idle dip when shifting from park/neutral into gear

[dville_gt]

Any way to fix this issue. Running a th350 and a 0411 pcm. When I shift out of park into reverse or a forward gear the load up on the motor messes with the idle. It will eventually figure it out, but sometimes (especially if I am in a hurry and don't take it easy) it will die.

Any way to adjust for this or to let the PCM know that the car is not in park/neutral anymore? I do have a park/neutral safety switch that I could use if it is simply grounding a wire to the pcm.

Thanks.

[mecanicman]

Do you have a speed signal generator?

[dville_gt]

Yes, I do have a pulse generator hooked up that reads correctly.

I see that the express van (what my PCM is from) has a Park/Neutral position switch. Any way to use this? The pin out is as follows:

32 - PRND A Signal
34 - PRND P Signal

and on the other connector

62 - PRND C Signal

[mecanicman]

I have had similar issues after swap. I used a 4 pulse per revolution signal generator and no park/neutral switch. I am not sure what the pcm looks for to switch between idle/moving tables, but at 4 pulse per mile takes a little longer(stock is 40). I compensated by turning idle portion timing up in all tables, turning idle up from stock 525 to 650, and open throttle blade more so relied on iac less. This was on a stock engine swap.

[dville_gt]

ya, mine is "okay", just have to be nice to it when you first start it up and let it have some time to learn. i'd like to get it "factory-like" so when i shift into gear it knows to expect additional load on the engine.

this car has a pretty big cam 235/240 .648"/.609" 111lsa so it the cam probably doesn't help me out at all with idle issues!

[mecanicman]

What year wiring pcm are you using, I will try post up wiring diagram for trans switch. You should be able to wire it up.

[dville_gt]

2004 Chevrolet Chevy Express G2500 6.0 L PCM.

I have the wiring scheme for it, but there are 4 wires that go to it.

PRND - A Signal

PRND - P Signal

PRND - B Signal

PRND - C Signal

I need to know what needs to be grounded/powered to indicate park vs. drive.

[mecanicman]

here you go

[dville_gt]

JEEEZ, that makes it a tad more complicated. If I only have a park/neutral safety switch that goes hot when I am in Park/Neutral can you think of a way to wire this up?

Since it is a combination of -/+ signals I'd need to figure out how I can make the switch. I dont care what gear it thinks it's in, as long as it thinks it is in either park/neutral when it is not in gear and in a gear when it is.

Any idea?

[mecanicman]

If you look at the wiring diagram, power is supplied in the pcm to each range. If you scanned those pids as you have them now, they would all show hi. To make them read low, you just have to provide a ground. So, for park/neutral just pick 2 to ground(either park or neutral, cant do both but wont matter for your purpose). For drive just pick one range and ground the required. Should be pretty easy.

[dville_gt]

So currently does the car believe it is in park or drive? If it thinks park would I just need to ground this inputs required to make it believe it is in gear?

[mecanicman]

currently it does not know what the hell is going on, I assume you have the codes disabled. With all 4 switches showing high it does not correspond to any shift pattern. I believe it would default to park neutral settings, and in the case of stock trans, you would only have manual reverse and manual 3rd.

If you just ground them to think it is in gear, you will have no change between loads and it will be no different.

[mecanicman]

K, If it were me I think I would hook the stock th350 park neutral switch up to A and P, so when you were in park the pcm will know it. I would then build a little bracket with wot switch being held closed when in park. When shifted out of park wot switch would ground all 4 pins signalling switch to gear. This would not allow for seeing a differance when in neutral, but how ofter do you use it?