1989 Suburban Stalling and Tranny Disengaging

Dave in GA · Jun 7, 2013

I've got a '89 Suburban 3/4 ton with the 350 with TBI and 400 tranny. It's my backup vehicle and not driven much. It's always idled strange like it struggles to hold a steady idle, trying to surge and slow down repeatedly. Now if I'm sitting at a red light, the bottom will suddenly drop out of the idle and it will stall. Starts right up again and the engine light comes on. Did that a bunch of times today. And now the tranny disengages sometimes when driving 40-50 MPH and the engine will race and all I can do is coast till it eventually kicks in again. Doubt if these are related, but not a fun day. On the engine, the distributor and IAC and O2 sensor are almost new, and all the tune-up parts are almost new. I don't want to spend a lot of money on shops trying to figure it out since the vehicle is a beater, but it's always been a reliable spare. Any ideas?

Mike in Mn. · Jun 7, 2013

I have seen them idle rough and start hard due to the shaft in the dist loose it's magnetism on the points that trigger the module, but you mentioned that yours was new. Unplug and plug back in the wires on the module, maybe a bad connecton? Make sure the module has a good ground and the dist. has a good ground to the engine. On the tranny maybe the filter is plugged?? I still run two 87's.

504-1 · Jun 7, 2013

This is not your trouble but twist the TB to see if the two halves are loose. That makes for a very fast idle, but check it anyway.

Bob · Jun 8, 2013

Some of the stuff posted here REALLY makes a guy scratch his head... there are NO "two halves" to the TBI used on a 5.7 of that era.

<img src = "http://i167.photobucket.com/albums/u125/27Grainfield/Stuff/57_TBI_zpsc9d37d48.jpg">

The body throttle body is all one piece. The injector "pod" sits on top, where a leak would NOT change idle speed, just let dirty air bypass the air filter.

There IS a gasket between the throttle body and the intake manifold and they DO fail and leak, often without any apparent looseness between the TBI and the intake manifold.

Bob · Jun 8, 2013

Not sure what's going on, but I'd say you have two separate problems, 'cuz the 400 tranny is ALL mechanical except for lockup.

I'd watch fuel pressure to see if that is lost when it dies, as well as put a test light on the red wire at the coil to see if ignition power is being lost.

If this is a 4X4, there isn't a grinding noise when the tranny appears to "drop out", is there? A failed shift fork in the transfer case can make them do stuff like that.

Allan in NE · Jun 8, 2013

Clear the codes, drive it until the check engine lite comes on or the problem arises. Then read the codes.

You can either guess and throw money at it all day long or just go see what the computer is trying to tell you with that CE light.

Repair the engine first, then see if you still have a transmission issue.

Allan

MarkB_MI · Jun 8, 2013

OK, you've got two unrelated problems. That's what happens when you don't fix things. If you're going to keep driving it, you're going to need rebuild the transmission. As for the stalling issue, this is one of those deals where you'll probably never find it on your own. My '88 had a nasty stalling problem, it would quit for a few seconds while running down the road at 70 mph, then fire back up. When it finally quit completely, I had it towed to a garage, where it fired right up! They hooked it up to their scope and left it running for several hours until it died. It turnrf out one of the wires on the distributor pickup coil was broken and making intermittent contact.

Dave Sherburne NY · Jun 8, 2013

I bought a new 88 chevy sub. and didn't drive it 2000 miles before it started acting like the transmission had real problems. Thought it would be out of service a long time for a tranny overhaul. Nope, dealer called a couple hours later said it was done, they changed the fuel filter. Ran it a lot of years after that with no problems

JimEvans · Jun 8, 2013

Fix the engine first. Sounds like a fuel problem. Could be Fuel pressure regulator, fuel filter, or fuel pump. what does the check engine light say? A paper clip and information available on the internet will let you read the codes.

fastline · Jun 9, 2013

Jeez, why was the very first reply not "what are the codes"??? Engine light on, not running right. That means the codes will likely fix your problem. Take a paper clip and short pins A and B in the diag port under the dash under the steering wheel. turn key on (not start), watch the engine light blink. The sequence tells you the code. Each is repeated 3x. Watch for ALL of them. Post them, I will tell you how to fix it.

This sounds like either a IAC circuit issue or TPS issue. The 400 is actually a 4L80 or 400 with OD. Solid trans with manual TV cable. Later models are 4L80E with full electric valve body. This truck should be stupid simple to fix. Never had a TBI chevy beat me.

Please understand this. This trans uses a eletronic TC lockup. It reads TPS to determine that value. TPS screws up, TC tries to lock, engine stalls like you dumped the clutch with no go pedal. GET THE CODES

1989 Suburban Stalling and Tranny Disengaging

Dave in GA

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Mike in Mn.

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504-1

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Bob

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Bob

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Allan in NE

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MarkB_MI

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Dave Sherburne NY

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JimEvans

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fastline

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