I've got an 89 Sierra. 5.7l 4wd Auto. When it gets up to normal operating temp. it stalls if left to idle. It runs fine if you are manually feeding it gas with the pedal. I drag a trailer with it and have no lack of power. It just dies when I come to a light or have to stop to change from drive to reverse.

I'm not much of a mechanic so that doesn't help. My haynes manual suggests checking several things. I've replaced the distributor, rotor,wires and plugs. I've checked all the vacuum lines. I've replaced all the emissions components. The only thing left to check according to the manual is the fuel filter for water etc.

You guys know better than I do, but it seems to me that if it were a fuel filter problem I would see other types of syptoms like struggling with a load or trouble starting. Maybe I have that way wrong.

I've read that it could be related to the torque converter, but the quick check of disconecting the wire has not improved the situation at all.

So, I know. Check the fuel filter. Fine I'll do that. In the mean time is there anything else I should consider? Fuel Pump?

The dern thing starts and runs fine as long as I don't have to stop or put it in gear while idleing. I get around OK, but I know this can't be good for the tranny and I can't let the lady drive it to get me candy wich is all I really want.

Any ideas?

Test the fuel pressure regulator. There is a vaccuum hose on top that should come off easily, if there is gasoline in the line, it is bad...replace it.

I'm sorry.

I've looked high and low along the fuel line and can not find a fuel presure regulator.

As best I can tell, the vacuum sustem in this truck only runs the emissions system. There are maybe 4 or 5 vacuum lines, tops, and they all connect to the TBI. None of these lead to a fuel pressure regulator.

I've read that these fuel pressure regulators are typically mounted to the firewall, but I can't find one on my vehicle to save my life.

Can you describe a better way of finding the fuel pressure regulator than following the fuel line from the TBI, down the back of the engine block and along the undercariage to the filter?

Is it possible that my vehicle doesn't employ this technology?

Thanks for the reply.

:banghead:

TBI's do not have a test port. You need to remove the fuel filter and install a special tool to test the fuel pressure.

The regulator is built into the TBI itself on the back where the fuel lines attach.

Has the pickup coil been checked or replaced? A bad ECT sensor (intake manifold) can also cause a low idle. Check all of the vacuum hoses for leaks.

//2000CAYukon

Also make sure the EGR solenoid holds a vacuum on the TBI side. I would also test the EGR (engine off, apply vacuum to the EGR, start engine, vacuum should have dropped to zero). EGR should hold a vacuum, with engine off.

//2000CAYukon

The EGR tests good. I even swapped it with one from another GMC I have and there was no change in performance.

The vacuum lines are all in in good condition.

I have not yet checked the pickup coil. I'd always thought I would begin to lack power if these things were malunctioning. I can swap it with one from my other truck tomorrow and have the old one tested and replaced if necessary. I'll report the results on completion.

I hate draining the radiator because it's winter here. Cold and wet are two great tastes that don't taste great together. But, I will replace the ECT and report the results.

Do I still need to have the fuel pressure tested if I do not have a vacuum actuated fuel pressure regulator?

I'd not said this before, but the truck functions completely normally when cold. Starts up fine, and does not stall when put into gear. The problem only presents itself when the engine is warm.

Thanks.

:banghead:

When the engine is warm, it runs in closed loop looking at 02 sensor values to figure out fuel trims. The ECT sensor is also looked at. Have it scanned to see what the engine is doing and what temp is being reported.

The idle is also lower when warmer and a weak pickup coil can cause a stall at idle. It goes away at higher rpms.

This does not sound fuel pressure related to me.

//2000CAYukon

I've put a new O2 sensor in. No change.

I'll go ahead and replace the ECT and pickup coil.

I'll have the computer scanned while running and report the results.

Thank you.

Take a good look at the vacuum hose going to the MAP. On my 90, the glue no longer held and it leaked between the elbow and the plastic hose. I only found this with a vacuum pump (would not hold vacuum).

A scan will tell you what the MAP is reading.

The PCV gromet is also a place where a vacuum leak can occur. They get hard and do not seal well.

//2000CAYukon

I replaced the pickup coil today. No improvement.

I'll have to do the ECT sonsor this weekend. I'll then report the results.

I'm betting this will not solve my problem so I will begin today the task of finding a mechanic who takes pride in his talent. Wish me luck. I'll need it.

Thanks for your help.
If any other ideas come to mind let me know.

:banghead: