So I just posted about transfer case oil, but since then my D1 has come down with a bad bucking and stalling issue. Under moderate throttle the engine loses all power and often will stall if I don't press hard on the gas. When I do push down on the gas it will roar back to life briefly and then go back to almost now power. Keeping it moving is a delicate balance on the gas.

I took a look at the common replacement items when I got the truck and it appeared like the fuel filter had never been changed, so I did that first. I was hoping that it would solve the issue and that it was just poor fuel delivery. I just gave it a spin around the block and it hasn't improved much if at all.

Searching around I see a few people mentioning the wheel speed sensor (or VSS) as a culprit in a few cases, but this was a somewhat sudden issue and I don't want to go down a rabbit hole of replacing parts if I don't know what the cause is. I've also seen multiple people mention it online, with very few answers about how the problem was fixed.

So if anyone has any experience with this, please please drop me a reply.

Thanks!

 

- check fuel pressure at the schrader valve on the fuel rail. should be >34 lbs/sq ft
- if you want to rule out the VSS just unplug it. You will lose the speedometer but if it is the problem, the truck will not display the symptoms you describe. I personally doubt this is your issue.

I would remove the air intake from the plenum and examine the butterfly valve. Have some carb cleaner at the ready. I'd also carefully remove the IACV and gently clean the pintle (important....try not too move the pintle in or out while you clean it).

Also check the wiring to your crank position sensor which located on the driver's side of the bell housing. It is often faulty due to the proximity to the exhaust pipes.


What year is the truck? (put it in your signature so everyone knows all the time)

 

Thanks very much for the reply. I'm learning quite a bit very quickly. Hell, I didn't know that the top cover was refereed to as the plenum. Truck is a 1996 SE with the standard evaporator system. I'm going to go buy or borrow a fuel pressure gauge today and check it. Then if it reads as normal I'll try and unplug the VSS.

Some more info: The idle seems normal as far as I can tell, issues only arise when I try and drive it around. It seems like it is more likely to stall when pulling up an incline, but I'm not 100% on that, it might just be that I'm needing to give it lots of gas to move it forward.

I highly suspect that this is a fuel delivery issue rather than an air issue. It seems to do it consistently.

I did just purchase the truck, so I cannot say if the hesitation was intermittent before this. But previous owner did not notice it (or is lying) and I did not notice it when I test drove it, or drove it home.

As I mentioned before, I did just change the fuel filter, and when I turn on the key to start the fuel pump I do not see any leakage around the new filter or clamps, so I would hope that it isn't just a failure on my part. The issue was present before I installed it, but I had already gotten the filter just because it's good to change.

Anyway, I'll report back if I get any more info. Thank you again.

 

also check the PCV oil separator on the passenger side valve cover, the hose which connects it to the plenum AND the 'S' shaped hose from the driver's side valve cover to the air intake near the IACV.

Us caution when pulling the oil separator out of the valve cover. Those little plastic pieces become fragile.

 

okay, update: I put the fuel pressure gauge on and got a reading of about 30lbs (5lbs below what you recommended) and it dropped pretty quickly down to the 20's. This is with the car off and the key in the on position. Based on my reading of the situation that means that there is either a blockage, between the tank and the injectors, or the fuel pump is on it's last legs.

Whatcha think?

Edit: Some details that should be mentioned. When the car is in Neutral it runs fine, reverses fine I can rev the engine and it will not die in either. It is only once it is moving forward in drive that the issue shows up. This makes me wonder if it is related to the MAF sensor.

Also because I am unable to purchase a car and not immediately have multiple issues, I also had a dead battery yesterday that I charged up and found dead again today. I swapped that out and I hope it's just an old battery, not a drain happening somewhere.

 

The fuel pump will shut off if there is no oil pressure, (motor running) after about 15 sec..

Had a similar issue where the truck would slow down to about 35 mph and then go back up to 55, i could watch the vss on my OBD scanner and see it jump al over the place. replacing the VSS took care of the problem. It is located where the speedometer cable used to go in the rear of the transmission.

 

very very interesting. I'll try and unplug the VSS shortly and test it out.

Edit: Tried unplugging it, didn't seem to eliminate the issue. I might be imagining it but it did seem better, but it still hesitated and threatened to stall under acceleration when doing a short loop in the parking lot. I'll check the fuel pressure when running next to verify that it is at the proper level.

 

Any codes? Check MAF, replacement corrected a very similar issue on mine. Created another issue, but that’s another thread.

 

Had a similar issue recently, I swapped the fuel pump (96 corvette works and only cost $21) and I found my crankshaft position sensor as well as the wiring to it was bad. No issues since repairing the wiring. 400 miles later, one roadtrip and some city driving.

 

Yea, I ended up taking it to a shop to do some diagnosis since I'm a bit too busy to hunt down the problem. They seem to think it's the MAF. I see from another thread that people suggest buying used ones off ebay, or trying to hunt down from other suppliers. I just called Rovah Farm and was told that the only real option are the reproduction ones, which he said have about a 1 in 5 chance of failing as soon as you put them in. So I'm a bit torn about what to do. There are one or two on ebay that are used and might be worthwhile, or I can spin the wheel of cheap ones and hope I find something worthwhile.

The shop claimed that the only source they could find with a genuine one quoted him $1600 for it, which is just nuts.