Vacuume modulator?

[Kellyboy]

So while driving my panty melter to work yesterday if I let off the throttle to coast when I got back on it it had no response for like 3 seconds then bang it would kick back on. It happened every time I let off. If I rolled to a stop it would idle fine and take off like normal. After work I popped the hood and found the vacuume line from the vacuume pump was cracked real bad where it hooked up to the modulator on the IP. I cut a couple inches off of it and hooked it back up. So far 3 one way trips to and from work have been flawless. My question is would a vac leak cause a hesitation on the IP or was this just a fluke fix that I can expect to return? Not really sure if the mod does anything to the IP or just controls the tranny.
thanks.

 

[goldneagle]

I would recommend you replace all the vacuum lines on that CUCV. Also replace the modulator on the tranny. It cost me less than $20 for all the parts and the truck shifts flawlessly.

 

[Kellyboy]

I would recommend you replace all the vacuum lines on that CUCV. Also replace the modulator on the tranny. It cost me less than $20 for all the parts and the truck shifts flawlessly.

Thanks. Definitely have to replace everything rubber on this thing. Good to know about the modulator on the tranny itself. Do you know if the modulator on the IP would kill the fuel supply if there were a vac leak?

 

[Rvitko]

There is a switch on the fuel pump which actuates the modulator to shift but I don't believe it would affect fuel delivery. The engine could bob down from being in a lower gear, my guess is you have a couple issues. A clogged fuel strainer or filter and vacuum leak. I would guess that as I just changed my fuel sending unit and the strainer and while I was down their I changed my modulator and hose which had a small hole in it. The difference is night and day, while it always drove ok, shifts were harsh but they happened, it feels now like I am driving a much newer vehicle and the shifts are barely noticeable and it is a lot faster to get going. The bad part is changing the fuel sender is probably the worst job I have tackled, one of those if it could go wrong it did, broken bolts, tore the first strainer I bought getting it in and I was working alone so I worked like a monkey holding the tank with my knees while blindly threading on nuts.

 

[Kellyboy]

Thanks. It shifts smooth and at appropriate speeds. Runs like a top except the quirky thing yesterday at highway speeds when letting off the throttle. Can anyone confirm the vacuume modulator in the IP would or not affect my ability to BRRRRAAAP!

 

[superB]

I had a bad vacuum pump which is at the back of the engine where the distributor is on a gas chevy engine, on my 6.2 diesel. It caused my transmission (400 turbo), to shift very, very hard, meaning like BANG, not smooth and easy, replaced it and all is good again..

 

[cucvrus]

When I have slow throttle response it makes me think of the metering valve, an air leak ,return line, or a fuel filter. Also lift pump could be weak. As long as you don't run out of fuel the injection pump has enough lift to keep the engine going even with a bad lift pump. Worth a look see. Does it shut off if you rev the engine at idle and then allow it to return to idle?

 

[Kellyboy]

When I have slow throttle response it makes me think of the metering valve, an air leak ,return line, or a fuel filter. Also lift pump could be weak. As long as you don't run out of fuel the injection pump has enough lift to keep the engine going even with a bad lift pump. Worth a look see. Does it shut off if you rev the engine at idle and then allow it to return to idle?

Runs perfect now. When it was acting up it would run normal at a stop and I could blip the throttle with no problems. Only acted up when getting back on it at highway speeds. No problems since I cut the bad vacuum line out. I have a screw on fuel filter waiting to put on as the stock filter was removed by previous owner and he just put a metal small engine inline filter on it. Lol. Probably not helping things.

 

[Kellyboy]

I had a bad vacuum pump which is at the back of the engine where the distributor is on a gas chevy engine, on my 6.2 diesel. It caused my transmission (400 turbo), to shift very, very hard, meaning like BANG, not smooth and easy, replaced it and all is good again..

Thanks, mine does shift hard at times. Not as bad now after fixing the vacuum line. Going to check the line on the tranny and replace the modulator on that end if it's easy enough.

 

[cucvrus]

The vacuum lines have no correlation to the fuel and acceleration of the engine. The small inline fuel filter maybe. But I am think it would really have to be clogged. many times I was glad I had the stock filter. I just had 2 bases repaired that I picked up a few years back. I had a machine shop tap and plug the pressure switch port. Total cost $50. for both. I pushed the switch back in to maintain the stock appearance and wiring.