87 R10 Cuts off at stop lights

[Jims86]

Thats where the VSS and IAC work together the most. As the vehicles speed reduces, the IAC stays open a little more so the engine doesn't stall.
Then after stopped, Idle settles to normal after a few seconds.

 

[MrMarty51]

So it let's the butterflies close gradually kinda like poop being tappered on the ends so your ******* don't slam shut. Right? Yeah, I know exactly what you're talking about. Maybe they do too now.

 

[MrMarty51]

Thats where the VSS and IAC work together the most. As the vehicles speed reduces, the IAC stays open a little more so the engine doesn't stall.
Then after stopped, Idle settles to normal after a few seconds.

I would like to shorten that time, when the IAC valve closes, sometimes I would like the extra braking power, like when pulling through the hills. it sounds Kooler too, when deceling and then, with the pipes I have, it gives off a different tone, that unwinding rappppp.

 

[Jims86]

I would like to shorten that time, when the IAC valve closes, sometimes I would like the extra braking power, like when pulling through the hills. it sounds Kooler too, when deceling and then, with the pipes I have, it gives off a different tone, that unwinding rappppp.

Its already programed to close all the way when the throttle is closed for a certain amount of time, at slow decelleration.

 

[cjbiondo89]

I appreciate everyones help...if it is fuel pressure issue why does it only do this when its at operating temp

 

[lee0123567]

Mine did the same exact thing. Check your fuel pressure. My dad and i checked it and it was at 7, depending on who you talk to TBI is suppose to run between 10-13/15. So we ran up to O'Reilly's and got a kit thing to rebuild the fuel pressure regulator. Runs like a raped ape now!!

 

[HotRodPC]

I appreciate everyones help...if it is fuel pressure issue why does it only do this when its at operating temp

You bring up a good point. That would lead me to believe it's going to be something controlled by the ECM. Most directions and monitoring do not take place until the water temp has gotten hot enough, and then the system goes into full closed loop operation. This is why it's important to know the that Temp sensor is not failing which Retro suggested. Things like TPS and VSS are monitored the second the truck is started. At any rate, I don't consider myself good enough with TBI, as there are others here much more fluent in TBI and TPI so I"ll let them walk you through this. I think TBI is supposed to be 14-19PSI fuel pressure IIRC. I'd still check the fuel pressure both cold and hot if you can. You may have a fuel pump that is thermally failing. Meaning it's getting hot, then weak. Rare but it does happen. Also, does it run any better with close to a full tank? Hate to have you fill it, then have to empty it if you need to drop it. But, this could help keep the pump cool if that's the issue on the heat, and if it's the soggy rubber hose which is not likely, it should be able to suck plenty of fuel. But, if it runs good on a full tank or close to a full than, then you pretty much know the problem is in the fuel tank.

 

[Jims86]

You bring up a good point. That would lead me to believe it's going to be something controlled by the ECM. Most directions and monitoring do not take place until the water temp has gotten hot enough, and then the system goes into full closed loop operation. This is why it's important to know the that Temp sensor is not failing which Retro suggested. Things like TPS and VSS are monitored the second the truck is started. At any rate, I don't consider myself good enough with TBI, as there are others here much more fluent in TBI and TPI so I"ll let them walk you through this. I think TBI is supposed to be 14-19PSI fuel pressure IIRC. I'd still check the fuel pressure both cold and hot if you can. You may have a fuel pump that is thermally failing. Meaning it's getting hot, then weak. Rare but it does happen. Also, does it run any better with close to a full tank? Hate to have you fill it, then have to empty it if you need to drop it. But, this could help keep the pump cool if that's the issue on the heat, and if it's the soggy rubber hose which is not likely, it should be able to suck plenty of fuel. But, if it runs good on a full tank or close to a full than, then you pretty much know the problem is in the fuel tank.

18-20 un regulated, 9-13 regulated at TBI. O2 is the only one ignored until closed loop. Quick way to check for a bad in tank hose, Is to hook up a pressure gauge at the filter. Lst guy that did it, only got a reading of 8 Psi, and when he dropped the tank, there was a pinky sized hole in the hose,

 

[HotRodPC]

Then I'm thinking of another system on the closed loop theory. What about the EGR? What's it doing until closed loop? Is it or is it not controlled by the ECM or is it just controlled by TVS? Could it be EGR Related? What else is controlled by TVS on a TBI system?

I think I've decided if I convert a truck to an ECM controlled system, I'm going to SFI Vortec or above.

 

[cjbiondo89]

borrowed a obd1 scanner...pulled code 34 map/vac sens lo and I pulled data and noticed it was rapidly running lean then rich lean then rich.....Map sensor reading were 38kpa @ 1.54v and TPS .82 (idle)

While in Drive with foot on brake Map is 55kpa @ 2.38v Temp @ 185 degrees (running for about 10 mins)


also when the scan tool starts pulling data check the truck instantly starts running perfect no almost cutting off hardly noticeable when you switch from park to drive as soon as you exit out of data check it instantly starts running like crap again???? Weird?

 

[Jims86]

borrowed a obd1 scanner...pulled code 34 map/vac sens lo and I pulled data and noticed it was rapidly running lean then rich lean then rich.....Map sensor reading were 38kpa @ 1.54v and TPS .82 (idle)

While in Drive with foot on brake Map is 55kpa @ 2.38v Temp @ 185 degrees (running for about 10 mins)


also when the scan tool starts pulling data check the truck instantly starts running perfect no almost cutting off hardly noticeable when you switch from park to drive as soon as you exit out of data check it instantly starts running like crap again???? Weird?

First, check for a leak in the vac line going to the map sensor, if its ok, get another sensor.

 

[benjaminearle]

borrowed a obd1 scanner...pulled code 34 map/vac sens lo and I pulled data and noticed it was rapidly running lean then rich lean then rich.....Map sensor reading were 38kpa @ 1.54v and TPS .82 (idle)

While in Drive with foot on brake Map is 55kpa @ 2.38v Temp @ 185 degrees (running for about 10 mins)


also when the scan tool starts pulling data check the truck instantly starts running perfect no almost cutting off hardly noticeable when you switch from park to drive as soon as you exit out of data check it instantly starts running like crap again???? Weird?

You might also try pulling the plug from the O2 sensor(s) and forcing open loop to isolate any potential feedback loop. That is, after you've checked the MAP sensor and fuel pressures (don't recall if you already did the fuel pressure bit)