Eliminate open loop prob after tans swap

[BowtieBlazer]

88 blazer just swapped a 700 r4 for a th400 since then my idle seems high and I was told that possibly the ECM needs to be told by a new chip with manual trans that the 700 is no longer there....do I have any other options where is the ECM located on this truck

 

[dyeager535]

I don't think that is your problem.

Pull the ECM fuse for 10 seconds, reinsert, start truck, but don't move it or put it in gear. What happens?

 

[BowtieBlazer]

I don't think that is your problem.

Pull the ECM fuse for 10 seconds, reinsert, start truck, but don't move it or put it in gear. What happens?

no difference

 

[southernspeed]

I don't think that is your problem.

Pull the ECM fuse for 10 seconds, reinsert, start truck, but don't move it or put it in gear. What happens?

Dorian, in the ECM Constants table there is a function for 'speed to enable open loop idle'. I'm wondering if, with out the 700 hooked up it won't drop into the warmed up, lower idle it might usually do? just guessing as I've not dealt with that function before.

 

[southernspeed]

88 blazer just swapped a 700 r4 for a th400 since then my idle seems high and I was told that possibly the ECM needs to be told by a new chip with manual trans that the 700 is no longer there....do I have any other options where is the ECM located on this truck

Is it higher in P/N or normal in P/N but high in D?
The ECM uses a different IAC setting for D and P/N. If the ECM doesn't 'know' it's in P/N it may be using the wrong value.
Don't quote me on this as all of the tuning I've done hasn't touched on these functions.

 

[dyeager535]

P/N is taken off the column, so if that was monkeyed with, it's possible I suppose, but I would imagine that target idle would compensate. The load on the engine from the converter is going to be pretty similar, and I've not heard of people with high stall converters running into idle issues.

 

[Thunder]

Just a off beat thing but. Beings it is winter. Is your heater set to defrost? That will jump the idle up.
Also check all your vaccum lines mabe something got knocked off or broke during the swap.

 

[BowtieBlazer]

it seems higher in P/N not in D I have looked all over at vacume issues and found non to speak of....

 

[dyeager535]

So no modifications to your P/N switch? How does the shifter "gate" work now with the 3 speed vs. 4?

 

[southernspeed]

it seems higher in P/N not in D I have looked all over at vacume issues and found non to speak of....

Have you actually driven it since the swap or disconnecting the battery? The IAC re sets after driving at 30 mph (I think) for a short steady distance.

 

[BowtieBlazer]

So no modifications to your P/N switch? How does the shifter "gate" work now with the 3 speed vs. 4?

I have not made any physical changes to the P/N switch the selector is obviously off visually

Have you actually driven it since the swap or disconnecting the battery? The IAC re sets after driving at 30 mph (I think) for a short steady distance.

I have driven it about 1000miles since the swap, since pulling the ECM fuses the in gear idle seems to have compensated and dropped even more the P/N idle has dropped some but is still high I am thinking about checking the timing again