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Truck stall when come to a stop, 87 FI 454

I know that rigs with the 700R4 trans have a solenoid in the tranny to unlock the converter when you come to a stop. TCC solenoid or Torque Converter Clutch Solenoid. If this doesn't unlock your converter when you come to a stop it is like stopping in a standard without pushing the clutch in. Just a thought. I'm not too familiar with the 400 tranny in that truck but maybe worth looking into. :thinking:

Phil
 
Just disconnecting the vac line to the EGR won’t rule it out. Last one that I had that failed would not close all the way due to carbon buildup. This caused the stalling on deceleration, which is typical of a EGR valve not closing fully.
 
EGR....mine did the same crap i changed the IAC and TPS checked all vacuum lines no dice. Threw on a new EGR and fixed all stumbling at idle problems, but i still have the habit of throwing it N when i stop at lights! :crazy:
 
Your EGR had to open up before it could attempt to close, no?

I know there are some negative backpressure EGR's, I don't really understand how they work, I suppose I could google it.

Eh, no different in reality. Vacuum applied, valve opens. If the valve gets no vacuum through the EGR solenoid, it can't open, therefore not stick open.
 
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OK, here's some info.

-VSS looks fine, follows speedo closely when driving.
-Swappd IAC, no difference.
-Plugged EGR hose as it left EGR solonoid. Truck stalled much less, mostly when stopped in gear and turning the steering wheel (power steering load).
I'm going to swap the EGR valve right now.

I'll post up.

Thanks,
Eric M.
 
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Pulled the EGR and cleaned it up a bit. Took a vac pump to it and it seems to operate well. I tried to blow through with it shut and it seals tight. Not sure if I'm going to bother replacing it unless one of you think it's wise.

Eric M.
 
I cleaned up the mounting surface and reinstalled the EGR with some Hi Temp RTV. I took it out and drove it around and could only get it to stall when I was backing into my driveway -Brake while turn - stalls.

I'm thinking this might be an intermitent problem that seems to be working properly for now ... I doubt cleaning and reinstalling the EGR was the issue. I'll take it out a few more times over the weekend and see if I can get it to stall more.

Something I remember from working on the TBI a little while back. I noticed the TPS was a bit slow to move back when the throttle was released. Not as free moving as the one in my other truck. I was thinking of changing it but ended up cleaning it with Brake Clean and got it to work a bit better. Could this be causing the problem? I could swap it with the newer unit in the other truck and se if it makes a difference.

Thanks,

Eric M.
 
I wonder if you've got a booster leak or something? If it stalls when breaking and turning, it's a possibility.

For the TPS, are you saying it doesn't "follow" the throttle linkage, or is the throttle linkage itself the problem? If it doesn't follow accurately, it's probably not helping things, thinking the throttle input is greater than it is.
 
The valve is normally closed, and has a little pintle that closes off an oriface. The problem is the pintle and pintle seat gets caked with carbon, and even when there is no vaccum the valve does not seal in the closed position. Sometimes you can just take the valve out and clean it with brake cleaner and will seal up ok.

dyeager535 said:
Your EGR had to open up before it could attempt to close, no?

I know there are some negative backpressure EGR's, I don't really understand how they work, I suppose I could google it.

Eh, no different in reality. Vacuum applied, valve opens. If the valve gets no vacuum through the EGR solenoid, it can't open, therefore not stick open.
Click to expand...
 
dyeager535 said:
I wonder if you've got a booster leak or something?

For the TPS, are you saying it doesn't "follow" the throttle linkage, or is the throttle linkage itself the problem?
Click to expand...

When you say booster, do you mean brake booster? I've got Hydroboost.

As for the TPS, the TPS itself is slow to pop back to the "no throttle" position. I took it off and worked it manually and it was slower to go back to the throttle closed position when released than the other unit I had. Throttle linkage is fine. I cleaned it up several months ago and it worked better, maybe it's sticky again and if so, that might be sending the wrong signal??


Eric M.
 
Definately replace the TPS switch. The ECM uses that for several functions and it needs to have a smooth movement and IIRC it goes from .5 volts at idle to 5 volts at WOT.
 
4X4HIGH said:
Definately replace the TPS switch. The ECM uses that for several functions and it needs to have a smooth movement and IIRC it goes from .5 volts at idle to 5 volts at WOT.
Click to expand...


OK, makes sense. I don't think I'll bother swapping the TPS with the other truck since I know it's gotta be replaced anyways. I probably won't get the part until Monday (got two baby showers this weekend, both ours!)

I'll post up when it's in.


Thanks,

Eric M.
 
Besides the TPS. Try unplugging the vac line to the EGR solonoid. See if that makes a diference. Sometines when they fail they stick open and apply vaccum at idle causing the EGR to open slightly.
Also you should not use any type of silicone where it can get in your intake system. Even a small ammount can take out the 02 sensor.
 
Thunder said:
Also you should not use any type of silicone where it can get in your intake system. Even a small ammount can take out the 02 sensor.
Click to expand...

Woops, too late. What's the error code for bad O2 sensor, 13? I guess I've got that to look forward to as well. Does the silicon have to break away and travel through the exhast system to cause an O2 sensor failure or is it just the silicon funes mixed with combustion that causes the failure?

I ran the truck with the EGR disconnected and still had the problem (not as much, but it was still stalling). I doubt it would be the solonoid if that was removed from the equation and it still stalled.

Thanks,

Eric M.
 
OK. Changed TPS and problem is still around. Stalls from time to time when coming to a stop. Sometimes stalls when turning the wheel while not moving (getting in and out of parking spots). Stalled once when decelerating while getting off a freeway ramp.

It is an intermittent thing.

Any more suggestions?


Thanks,

Eric M.
 
Almost sounds like your idle is too low. I would assume you'd post up if it were...?
 
dyeager535 said:
Almost sounds like your idle is too low. I would assume you'd post up if it were...?
Click to expand...


Yes, the idle seems fine, scan tool shows it is where it should be.

I'm wondering if I have a leak in the throttle body, a bad gasket or seal that is allowing fuel to pass into the TBI flooding the engine. Does that make sense?


Eric M.
 
Throttle body vacuum leak could cause issues. You can test them (I like the propane method myself), it never hurts to verify. It is a problem with these setups.
 
Things are worse now. Engine will not idle in park or drive. It drives fine, all is well as long as my foot is in the throttle a bit. But, let up on the gas and it sputters and dies every time now.
I have another 87 TBI, 454 truck that runs fine. I'm swapping parts to locate the problem. What I have done so far:


Disconnected EGR solonoid from EGR valve
Swapped EGR valves
Swapped TBI (entire unit, unbolted from manifold on one truck, bolted to the other)
Checked for vac. leaks with carb cleaner (manifold, surrounding area, EGR, TBI, etc.)
Checked timing
Swapped MAP sensor
Plugged all vac. ports at TBI
Plugged manifold vac. outlet
Vacuum at manifold is 15 to 18 with idle is as low as I can get it before it stalls
Voltage is OK
No codes
Scan tool shows all sensors working within their perameters, except, IAC will go beyond 60 count when engine tries to idle (before stall)
Swapped oxygen sensor
Swapped ECM


Thanks,

Eric M.
 
Here is what i would check next. Paperclip the A & B terminals on the ALDL connector then turn the key to the on position and go listen to the IAC motor and make sure you can hear it. If you can hear it leave it like that for 30 seconds then with the key still in the on position disconnect the IAC plug, this seats the IAC motor and prevents a vacuum leak at this point, (IAC is a controlled vacuum leak through the ECM). Now turn the ignition off and remove paperclip and start engine. If it idles now then there is something wrong with the IAC motor or the ECM (doubtful of IAC if you have same symptoms with different TBI unit installed).

If you don't hear the IAC motor when the ALDL connector is jumped and the ignition in the on position then it's probably and ECM problem.

Have you swapped the ECM's ?
 
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