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Ask GM Tech (Cam) Your Own Question

GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27661
Experience:  GM Grand Master Technician 2007. 11 years experience.
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1996 Chevrolet: 2500 with the vortec 5.7l

Customer Question

I have a 1996 Chevrolet K-2500 with the vortec 5.7l. engine. I have installed Irridium plugs, 10mm.wires Higher voltage coil, aFe two stage enclosed cold air box, Helix power tower, V_Max riser in the intake , Replaced the SCPI injection with the GM MFI unit,Made sure that I am carrying the proper tire pressure, replaced the rear diff. with synthetic and cannot get more than 11mpg ! I drive 30 miles to work at 62mph and still cannot get better mileage. Help! what do I need to do yo improve my mpg.
Submitted: 2 years ago.
Category: Chevy
Expert:  Dr.Automotive replied 2 years ago.

snapontech :

Welcome to Justanswer, My name is XXXXX X am here to help.

snapontech :

city/highway/combined 12/16/12.9 So based on this the MPG is very close to what it should be

snapontech :

And most of the time you cannot get the estimated miles per gallon

snapontech :

The 5.7 is a gas hog 350

snapontech :

These trucks decrease massive amounts over 60 MPH

snapontech :

You show you are driving it at 62 so this makes sense

snapontech :

If you want to increase the MPG make sure oil is good new fuel filter drive it very easy and keep it under 60

Customer :

I have studied specs on the parts that I installed. All items were touted to improve HP and mpg ! I have not gone into the ecu other than to dissconnect the battery and restart the truck. No fault codes have shown up from anything I did.

snapontech :

I can understand what your saying but this vehicle is not a friendly MPG vehicle.

Customer :

If I went with all advertised promises I should have over 350 horsepower and 400+ torque.

Customer :

Along with at least 5+mpg.

snapontech :

These have good torque but the K2500 is heavy

snapontech :

Are you experiencing less power than you should have?

Customer :

No

Customer :

I can feel more power and possibly torque. Forgot to tell you about Magnaflow and headers.

snapontech :

Yes these are great for power not MPG

snapontech :

I recently had a tahoe with 38s and it was terrible

snapontech :

I had every mod done as well

snapontech :

Tried the no brake pedal and very little gas pedal and in town 5 MPG

snapontech :

So I am very familiar with your experience

snapontech :

You could do a cleaning on the engine

snapontech :

Seafoam

snapontech :

This can help the engine run smoother and gain some loss of MPG

Customer :

done already

snapontech :

Do you still have the O2 sensors?

Customer :

yes ?

snapontech :

I suspect your vehicle is doing the very best it can do I wish there was something more I could offer you have done all the small things that can help. I know its within the spec from the manufacture but this is not very good

snapontech :

You could have a lazy O2 sensor but normally it will give a code

snapontech :

Since its running great this doesnt exclude the O2

snapontech :

Because the O2 only helps when the engine is not wide open

Customer :

not one code from anypower adder.

snapontech :

I dont believe the mods will cause trouble but on the older gms the codes will only come on when there is a major problem and sometimes not even than

snapontech :

You need to have the O2 checked with a handheld scanner to verify they are not lazy

snapontech :

Bad O2 can easily lose several MPG

Customer :

If its the o2 sensors than there should be a fault code at some time .

snapontech :

No this is not true

snapontech :

The O2 can be lazy but not dropping long enough to set off the CEL

snapontech :

I see it alot.

Customer :

Well its pretty late , so I cannot at this time validate your theory. With the holidays apon us it will be at least a couple of weeks to pull the sensors and have them checked or replaced.

snapontech :

Ok, I know the MPG is very close and considered to be within range the Estimated MPG is on a brand new one back in 1996 all stock so you have to believe it will not keep that when older. The O2 is a MAJOR difference maker in MPG so if this is old and not working as it should than you get lower MPG

Customer :

I at this time do not think that the sensors could hold back all of the Power adders that much.Sorry.

snapontech :

You said the power was goos

snapontech :

good

snapontech :

The O2 sensor doesnt effect the powerband

Customer :

So if you would like to revisit this in a couple of weeks , my opinion may have changed.

snapontech :

After a highway road test, check wheel hub temperature with an infra-red temperature gun and compare to each other. Clean the Mass Air Flow (MAF) sensor elements and the fuel injectors. Verify Engine Coolant Temperature (ECT) value when driving, should remain near 190-195 degrees F. Check knock signal activity when at highway speeds, look for high timing retard values. Watch short term fuel trim and long term fuel trim values for each bank while at highway speed, should be in the +/- 10% range. Verify that the fuel type is the same as was used prior to the MPG drop.

snapontech :

At speeds above 60 MPH, it is likely that the fuel delivery will stay in an "Enrichment" mode.

snapontech :

NOTE: Not likely to obtain much better than 11 MPG at 60+ MPH with this vehicle.

Customer :

The front end has new hubs( one of the sensora for the anti-lock was bad) ,new rotors ,new pads.

snapontech :

This is the proper information I am very sorry but that is how the vehicle was designed

Customer :

Front end alignment , and I use a mid grade of Shell gas ( No knocks0.

snapontech :

You cannot find knocks with your ears

snapontech :

You need to monitor this with a scan tool

snapontech :

The system will change the timing if its falsly detecting knocking at all

snapontech :

Are you running stock size tires

Customer :

yes

Customer :

245/70 16

snapontech :

The only thing I can suspect is this is in enrichment mode which is based on the values from the sensors. If the vehicle is being driven easy than you should be able to do better but if its in enrichment mode you will need to find out why without a scan tool its impossible to tell

Customer :

I am not dissatisfied , just not hearing anything new.

snapontech :

A trick you can do without even checking is The reference low circuit can shift to cause the HO2 to sense incorrectly. If adding a ground to the reference low circuit changes operation and helps the condition, add a permanent ground to the existing reference low circuit. Do not disconnect the existing circuit.

snapontech :

Replace the fuel pressure regulator and also the PCV valve

snapontech :

Check the cam retard again need a hand held If cam retard is not 0 plus or minus 2 and no one has moved the distributor, inspect the distributor drive gear for excessive wear. Verify the reluctor wheel on the crank shaft is tight. Replace the distributor shaft; the reluctor for the cam sensor has slipped.

snapontech :

That is about everything you can possibly do to correct the problem

snapontech :

And there is nothing more I can add Let me know if I can further assist in your issue here. If I have assisted please kindly press the green ACCEPT button this is the only way I get credited for my time and effort. if not let me know. Thanks in advance Danny

snapontech :

You can come back anytime for the same problem with me at no additional charge

Customer :

Well I would like to discuss more , but without more answers to questions that have been proposed ? I just am back to the beginning. PCV and fuel reg have been changed. will have to check on the dist. wear.

snapontech :

I understand

snapontech :

I have given you all the possible causes

snapontech :

Have you also added the ground

snapontech :

If you need anything else let me know

snapontech :

I can send this to the other experts if you would like

Expert:  GM Tech (Cam) replied 2 years ago.
Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.

I have a couple questions

1- are the cats still in there?
2- what octane of fuel?
3- what st he rpm at 60 mph.
4- what is the rear end ratio?

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