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Truck stall when come to a stop, 87 FI 454

Eric M.

Eric M.

1/2 ton status
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87 V3500, Fuel injected, 454. It starts fine, runs fine when cold, if fact runs fine when at temp. too, but, dies when I come to a stop. It will run a few seconds, and then, RPM drops and engine dies. If I kick it into neutral, it's fine.

Any ideas before I start disassembling all the wrong stuff?

I was thinking IAC?

Thanks,

Eric M.

THE FIX
The distributor needed to be replaced.

From what I got from the Service Manual, the IAC uses 3 sensors, the temp., TPS and distributor.
If the TPS is fully closed the IAC will function, if it is open at all, it won’t function.
If the engine temp is low (cold engine), the IAC will adjust for less air at idle.
The IAC will adjust for more or less air to maintain the proper RPM based on RPM signal from the distributor.

Apparently, the distributor was not sending a correct RPM signal to the ECM at lower RPMS (idle).
I did check the RPM reading on my scan tool while trouble shooting and it looked correct. I was never able to get the engine to remain at lower RPMS long enough to see if the reading as erratic.
 
Last edited:
Any trouble codes?
You could try cleaning the IAC. Check the EGR for proper function should be fully closed at idle.. Vaccum leaks? TB base gasket?
 
ONLY coming to a stop? Stabbing the throttle in park/neutral doesn't cause it?

Cruise control? Does it work? (assuming it hasn't been butchered)
 
Thanks.

I didn't think about the EGR, I'll look into that one first then check for vac. leaks and TB base gasket.

Dyeager, to answer your questions:
-No codes.
-Only when I come to a stop while in gear will it die. If I put it in neutral when coming to a stop sign, it won't die.
-Stabbing the throttle in park or neutral won't make it die.
-Cruise Control is hooked up and working (I think, haven't used it for some time now). Should I take it out and try the Cruise Control?

Thanks,

Eric M.
 
Not sure about TBI but when i did a TPI conversion years ago i forgot to hook the VSS up and it did the exact thing your's is doing and it did not throw a code.
 
Yep. VSS may not throw a code, I've driven around without mine hooked up for testing/proving purposes, and the longer driven, the worse idle/stopping was. Manual transmission somewhat changes dynamics of stall, but idle quality deteriorated quite rapidly.

Cruise uses VSS, so if cruise doesn't work, it MIGHT be VSS. Even if cruise does work, a scanner is your best bet to see that the ECM is getting the speed signal.
 
I'm thinking I don't have a VSS on my rig. It's a Turbo 400 and a 205. I've got a speedo cable, a 4WD light switch and a neutral safty switch - that's all I can remember without crawling under te truck. Doesn't the cruise control on the 87 get it's info. from a sensor mounted in the back of the speedometer?

Let me know if I'm right about this, I can take a look under the truck as well.

Thanks,

Eric M.
 
Eric M. said:
I'm thinking I don't have a VSS on my rig. It's a Turbo 400 and a 205. I've got a speedo cable, a 4WD light switch and a neutral safty switch - that's all I can remember without crawling under te truck. Doesn't the cruise control on the 87 get it's info. from a sensor mounted in the back of the speedometer?

Let me know if I'm right about this, I can take a look under the truck as well.

Thanks,

Eric M.
Click to expand...

Green rectangal box behind speedo is the VSS. There is a plug that connects just to the side of the speedo cable.
 
Ahhh, thank you!

I haven't dove into this yet, Maybe tomorrow or Thursday. I'll post up what happens.

Eric M.
 
x2 the green box, one line goes to the ECM, the other feeds the cruise box. All injected GM vehicles have VSS.

Better off checking it with a scanner, it's a circuit board, no way to figure if its working or not unless the wire(s) are cut, which is unlikely. Autozone has scanners that are free for use.
 
dyeager535 said:
Autozone has scanners that are free for use.
Click to expand...

I've got a scanner, I'll plug it in today and check it out. As far as checking the VSS, am I looking for the MPH reading while driving? Is that the bst way to check the VSS.

Thanks,

Eric M.
 
Yep, speed signal while driving. If the problem is consistent, then you'll know whether VSS is the cause/culprit. It should match up to your speedometer, but speed accuracy is AFAIK irrelevant to anything other than converter lockup in the 700R4.
 
Right, but as long as the ECM knows the vehicle is moving, if the MPH are off (gear or tire change without speedometer correction) it's not going to matter. It still knows idle in gear vs. moving/coasting/stopping.

If you were getting an intermittent speed signal, or none, then IAC would be affected.

As many people that disagreed with me on the importance of VSS to TBI trucks, I do have to say that VSS being the issue is probably unlikely. I suppose I could test on my TBI truck at some point, but based on what others have experienced, VSS is quite unimportant to TBI, which is not true for TPI, which is what I have more experience with.
 
dyeager535 said:
I do have to say that VSS being the issue is probably unlikely. I suppose I could test on my TBI truck at some point, but based on what others have experienced, VSS is quite unimportant to TBI, which is not true for TPI, which is what I have more experience with.
Click to expand...

Thanks, unfortunatly, I haven't had time to take a look - work and a baby a month away has me running around. I'mtrying to get some time today, but I'll keep in mind it may not be the VSS. I'm leaning towards EGR or maybe IAC.

I'll post up, hopefully later today.

Thanks again,

Eric M.
 
Just in terms of actual problem/resolution, EGR is FAR more likely than IAC to be a problem. IAC is pretty easy to play around with of course, if you just feel like removing and cleaning it. :)

But since you've got a scanner, VSS is easy to rule out.

EGR is usually pretty easy too, disconnect it, (I'd disconnect the vac line to the solenoid, and plug it in case of a bad solenoid) see if the problem stops.
 
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