I have a 97.5 Turbo that I'm having stalling issues with. I was having a starting issue, the truck would only start intermittently even in neutral. I replaced the neutral safety switch and now it will almost always start. However lately I'll be driving around town and it will stall out on me as I'm coming to a stop or stopped waiting at a light. After stalling the truck won't start up again for about 10 minutes. My idle rpm seems kind of low(650rpm) and they drop even more whenever I press on the brake almost to the point of stalling, theres some hesitation. I need a new vacuum pump as my AC doesn't blow through the vents, and I'm about to replace it. Would the Vacuum pump be enough to make me stall out? I've read about the PMD and it's issues which sound similar, and mine is still in the stock location. I've had the truck for two years and haven't gotten around to relocating it. Any help or insight would be appreciated thanks!

 

The vacuum pump shouldn't cause you to stall unless it is seizing up. You can do a quick check by undoing the belt tensioner and trying to rotate the vacuum pump by hand. It should be fairly easy to rotate with little resistance. My vacuum pump completely died a few months back, but was still able to rotate freely. I only lost boost to the turbo and the HVAC vents would not change position.

 

Alright so I changed out the vacuum pump today and still nothing coming out of my HVAC vents. Also changed the blower motor resistor and the blower motor relay? What else could be causing my vents to not blow air, and also still stalling out even at idle. Wait 5 minutes and it cranks right back up. Is it more than likely going to be the PMD/FSD?

 

For your HVAC, there is a fuse underneath where your knees are in the driver seat fuse box for the low fan speeds, and an inline fuse under the hood coming off of the alternator for the high speed fan speed. Check to see if those are blown or not. If your blower motor is working but you can't switch head/feet/defrost modes, it is likely a cracked vacuum line coming from the turbo to the boost solenoid valve, or from the boost solenoid valve to the vacuum pump. Otherwise the boost solenoid valve could be dead.

 

Alright so when I disconnect the line coming from the vacuum pump to the boost solenoid I can feel it sucking air. However I can't feel anything on the left side of the solenoid where there is a small black hose connected to it. Should I be able to feel suction? Is there another connection at the solenoid that I might be missing? Also air will only blow out the defrost vents on the high setting and not on any of the others. I have checked all fuses, and all the relays that I am aware of and I replaced the resistor on the firewall.

 

Stalling issue sounds like a failing PMD. You can speed up the restart by pouring cool water on it but the PMD is telling you to replace it before it fails ompletely.

 

I plan in replacing the PMD soon with a relocation kit. I noticed today that the current one is one of the grey stanadyne units and I've read a lot of bad things about those.

However I made a small breakthrough in the A/C but Im even more confused now. I cleaned the connector to the blower resistor and I am now getting air through the dash vents on High speed only, whereas before it would only blow through the defroster vents on high speed. I thought it only defaulted to defrost when there was a vacuum issue? How can I get my low speeds to work now? I think they are controlled by fuse 7D right? I tested it on a meter and it's still good. What else would I be missing?

 

Still sounds like a vacuum issue.

 

So the low speeds not working would be a vacuum issue? Why would it blow out the vents on high but not low if there was a vacuum leak?

 

The vacuum line only controls the louvers in the HVAC system to select between vent modes. If you have that working, there isn't a vacuum issue.

The low/med/high speeds on the fan control are either a wiring issue, resistor block issue, or a HVAC control unit issue (the thing with the speed/vent ***** on it).