Can a bad PMD = poor fuel mileage?

[mfgguru]

My trucks mileage has just been getting worse and worse. I get about 420kms(262 miles) to about 80-85 liters( 21 gallons) of fuel. It has been surging in reverse more often now than ever. The PMD was mounted on the intake for about a year(from new) and now resides behind the grill for the last 3 months. I would like input on the following:
1. Can the PMD cause poor fuel mileage?
2. Is the surging caused by a failing PMD?:incazzato:
3. Will new injectors see gains in mileage?:gnorsi:
4. Can my IP (original) be failing?:sifone:
5. Could there be any other reasons why my fuel consumption is so high?:cuss:

Thanks,
Mike

PS: I don't speed, EVER! I know, that's boring!

 

[iamdave0887]

your right foot has to do alot with fuel mileage. yes surging is a symptom of a failing PMD. eventually it will get to the stalling stage if it hasn't already. i'd say get a heath kit and never worry about it again.

 

[Acesneights1]

Check your lift pump. Don't ask me why but when mine wasn't working I saw a 3-4 MPG drop. My injectors had 165k Miles on them and new ones didn't do squat for mileage. The only mod that improved it slightly was opening up the exhaust.

 

[mfgguru]

I put a new LP in about 3 months ago. I will have to install a pressure gauge and check to see what the scoop is.

 

[JMJNet]

There are high occurences of bad OPS. My dad's suburban, he changed the OPS 2 weeks ago and drove it for about 1000 miles, guess what, it already gave up. The Sender part to send the pressure is working, the switch part that send electric is not.

There are some solution out there using an additional relay. He made up something using the existing relay hooking it with the GP fuse. Override the OPS, may not be kosher. Now the LP turns on as soon as he turns the ignition.

 

[JiFaire]

The simple answer to your questions is yes.

Failing PMD can cause misses, gaps, lags in response, pulse timing issues, the occasional heart-stopping hiccup when merging onto the freeway, etc.


You aren't running your buddy's biofuel, are ya? That will drop your mileage, too.

 

[mfgguru]

Nope, but when I run a 10% blend of bio, I see a better mileage rate than without. There seems to be a lot of controversy around BIO (real reacted biodiesel). I don't want this to be one of those thread. Thanks JiFaire.

 

[Turbine Doc]

FYI all; his is OBD-II, dead OPS will not kill all power to lift pump, on OBD-IIs there are 2lift pump power paths PCM & OPS to lose all lift pump power you have to lose both inputs, OBD-I however lose OPS you lose the lift pump power.

 

[Turbine Doc]

FSD might cause it but since IP & injectors are starting to get long in tooth as far as mileage goes my suspicions reside there more than in FSD, have you run any lubricity additives in it other than bio-D, what is your timing at, have you done an optic bump, was mpg loss before or after the B&M shift enhancer addition

 

[mfgguru]

I occasionally run some Kleen Flo fuel conditioner through it. Maybe every 10 tanks or so. I have not done any timing changes. To be honest that kinda scares me a bit. I can get a snap on scanner from a friend of mine and check it out. What needs to be done to check it and what should it be set at for best efficiency? I have noticed a drop in mileage after the shift enhancer was put in. Could that do it? I did put in a rebuilt trans as well. I guess I need to get the HPT and have all the mods right in the programming.

Injectors are going in this week. Chris K. set me up with the procedures.
Should be fun!