stalling with low gas in OD but not in D

[roadwolf]

1987 silverado 5.0 th700 r4 35x12.5x15 not cat glasspack

sometimes when cuising at low speed in OD the engine stall, it never happends if i am in D. do you already have the same trouble or an idea of what could it be ?

bad TPS ?
timing advance ?
fuel line trouble ?
trany trouble ?

 

[89Suburban]

EGR issues maybe?

Getting a check engine light on when this happens?

 

[roadwolf]

No check engine light, but i never seen the check light even when i put power on, it is probably not wired.

 

[sticman]

1987 silverado 5.0 th700 r4 35x12.5x15 not cat glasspack

sometimes when cuising at low speed in OD the engine stall, it never happends if i am in D. do you already have the same trouble or an idea of what could it be ?

bad TPS ?
timing advance ?
fuel line trouble ?
trany trouble ?

Since the low fuel condition and D doesn't cause the stall condition while cruising.

I assume your are cruising down the hwy at, over, or somewhere around the 45mph (70km) range. Some cruse speed that causes the problem when the transmission is in, or shifts into overdrive. The motor starts to slow down, possibly lugs to its stall point. If the motor just quits randomly then a different direction may be needed.

If i guessed close, then..

I'm going down the rpm is too low during cruise in overdrive path.

Cruising in OD should net the motor rpm somewhere around 1500rpm mark for starters.
Sector in D when transmission shifted through all gears = higher final cruise rpm then having the sector in OD = lower final cruise rpm .

I my self would confirm the rpm of the motor while cruising and just before the motor stalls (probably under the 600rpm at stall point) while in overdrive, selector in OD. To confirm whats happening to the motor rpm while cruising.

Wire in a temporary tach or if your truck still has its on-board computer plug in with a scanner and see what's the live rpm of the motor.

I got a cheap tach for $26 its a great tool to have in the tool box.

If the motor sounds like its lugging while cruising, the rpm is too low.

With a 700R4 in D you should only have 3speed operation in OD you should have 4speed operation.

Final ratio? Tire size, axle ratio and 4th gear overdrive ratio combination might be the problem.
HWY gears less than 3.73 gear ratio and 35's would most likely be not be a good combo. Eg. 3.08, 2.73 ratios ect.

There's all sorts of online final ratio calculators where you can calculate where the rpm will end up for a given final ratio.

I cant remember if the early 700r4's had lockup torque converter operation, this could also be the problem, or problem with the electro / vacuum circuit that controls the converter locking unlocking.

 

[roadwolf]

sticman, i think the same thing, to low rpm due to big tires.

i does not happend often to me but my wife that drives slowly have the problem.

i don't have tach in my truck, but i'll try with digimoto software and a "obd" interface that i use for my 1999 silverado.

 

[Jims86]

When did you install the 35's, and did you change the speedo gear when you did it?
Speedometer also determines 3rd gear and OD lockup via the Vehicle Speed Sensor.
I dont think that ODB interface will work with OBD 1...most dont, they are all for obd 2.

 

[sticman]

Jims86 has a good direction as well. Computer should know speed of the truck as well.

If your scanner is obd2 only, you'll need an older scanner or you can use WinALDL - 160 baud ALDL reader and build your self a simple interface cable with a computer that has a "real" serial port to get the live data that way.
I've had success with this software.

 

[Jims86]

Jims86 has a good direction as well. Computer should know speed of the truck as well.

If your scanner is obd2 only, you'll need an older scanner or you can use WinALDL - 160 baud ALDL reader and build your self a simple interface cable with a computer that has a "real" serial port to get the live data that way.
I've had success with this software.

^^^^This is a neccessity for any OBD1 vehicle owner, IMO.
the ECM PROM is programmed to lock the TC at about (aboat for Canadians)31 mph in 3rd, and 38 mph in 4th based on a 3.42 gear ratio, ad stock tires which were 235/75-15. should only unlock about 2mph under those speeds in the respective gear, if the brake pedal is depressed, or the throttle is increased.
That said, with 35's, that thing sould take a mighty long time to go through the gears. And, 700r4 dont like those low rpms...will burn it up quick.

 

[roadwolf]

I bought it with the 35 tires on it, so i don't know if mods've been done to the speedo gear,

i am planing to buy a actron cp 9190