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94' 2WD Pickup
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Discussion Starter · #1 ·
Just looking for a little input on why my mileage my be off.
First I will address what I have done to the truck as of late and throw out suggest as the next direction to take.
I have have recently installed new NGK plugs and wires, Factory distributor cap and rotor, Factory O2 sensor (in Spring 06), Factory fuel filter and PCV valve, Factory belt, Seafoam and Chevron w/Techron treatments, and an Oil and filter change. The truck is running smooth and no real noticable problems except for one. Very sub par fuel mileage, on average I get about 21-23mpg on average, with city and highway combined. The norm was at one time around 27-28highway and 23-25city.
I ran the codes recently and the only thing that came up was the EGR code (71).
I am getting ready to perform a coolant flush and refill with Factory Red antifreeze, new thermostat and new hoses. On Monday I am going to send out my injectors to be cleaned, rebuilt, and balanced. Then am going to fully clean and rebuild the intake manifold next weekend. I am also planning to adjust the valves tomorrow morning (No work tomorrow...sweet!).
What I am looking for is advice on what to look for to correct the poor mileage. See truck info below!
I know I also need to take into account the fact that the engine has 235K on it and the cold weather also affects things.
Any suggestions would be greatly appreciated.
 

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code 71 usually pertains to exhaust gas temps being too high. its commonly associated with the egr gas temp sensor or a lean condition. im not sure how that would make sense since your mileage is off but if i was getting that kind of mileage i would be incredibly happy. im curious to see what happens after you get your injectors serviced. if you have a vacuum leak it can also throw a 71. sometimes the vacuum lines can have cracks without much indication. another thing to look at is the cold start time switch / cold start injector and the coolant temp sensor(not the switch ) it could be allowing the cold start to actually richen your mixture causing poor mileage. your throttlle bod would be another place to look specificly the iac which is a non servicable non adjustable part. its an expensive part to replace and i dont think its your issue.
 

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94' 2WD Pickup
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Discussion Starter · #3 · (Edited)
Sub,
Thanks for the info, I've had the egr issue for some time now and am fairly certian that is not my problem. But one question, what is "iac"?
 

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94' 2WD Pickup
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Discussion Starter · #5 ·
Alright....where is it located?
 

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Discussion Starter · #7 ·
There are several place that do this. I would look around on the net.
Here are a few links with further information:
www.rceng.com
www.cruzinperformance.com

Check them out a lot of good info.
 

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the idle air controller is a temerature controlled air valve that is attached to the bottom of the throrttle body. it has a small 5/16" coolant bypass hose that uses coolant temp to adjust your fast idle speed and idle mixture. it is not adjustable and is not servicable if its worn, im not sure how to test it either. i bet a fuel injector ballance or fixing a possible vacuum problem will help your mileage. have you tried a new egr? i mean try it if it doesnt help use the warranty to return it. ive done that before, it seems petty but i just tell them that one of the other guys told me that the part i needed and it didnt work. plus if it does work then you dont have to bother with returning it. does your truck have the egr temp sensor? if so you might want to try that too.

i know that the egr is really sensitive to vacuum preassure also if your compression dropped or isnt within the factory specs. you may also have a bad or clogged egr modulator or the filter inside the modulator. you may also have a bad vsv for the egr and or pair valve system. all that emissions stuff can be a real bitch , i remember having to take the ohio e chack every 2 years, did your truck pass? im assuming it did.
 

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Did you have the 17" rims when you were getting better gas mileage? I couple of mpg is going to be lost by using fat sticky tires over skinny 14" 75 or 70 series rubber.

In the winter it takes longer for the fluids to get up to normal operating temperature. Colder temperatures also mean less air pressure in your tires.

Many communities mandate "winter" gas. Two or three MPG is lost right there.
 

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94' 2WD Pickup
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Discussion Starter · #10 ·
Sub,
I plan on going through the EGR system tomorrow, so we'll see what develops. As for the echeck the last time I went I did pass, however echeck no longer exsists in Ohio, at least in southern Ohio.

TurboJim,
I have 16's on right now, but some of my best mileage has been with my 17's. Also I have heard that winter gas formulas worsen gas mileage.
 

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Discussion Starter · #11 ·
Well I never got around to checking the EGR and I have to go out of town for a week for work therefore won't get to work on it any this week, maybe a little on the weekend. We shall see.

If anyone else has any suggestions or thoughts on the matter I would really appreciate it.
 

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Languishing in Virginia
1994 XtraCab 4x4 P/U
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I vote vacuum leak like subliminal said; there are ten miles of vacuum hose on these puppies...
 

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YOTA Master
'93 2wd P/U
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2,434 Posts
First:
Code 71 EGR system malfunction. This code happens when the ECM thinks the EGR should be working and it does not see a corresponding increase in temperature as measuered by the EGR temp sensor. This can be caused by a problem with the EGR valve, Clogged EGR passage, no vacuum signal to the EGR valve or a problem with the EGR temp sensor. If the EGR valve is not working the most likely symptom would be pinging. Which could result in the ECM retarding timing. this would have a negative impact on fuel consumption.

So it would be a good idea to find out what is wrong and fix it.

Second:
Exhaust leaks (even small ones) upstream of the O2 sensor will drive the fuel mixture richer and hurt your fuel economy.

Third:
Cold weather is a notorious mileage killer. This usually has a bigger effect on vehicles with shorter drive cycles. if this is the primary culprit you will find on an extended highway trip that your mileage will be closer to normal.

Finally:
Injectors on older vehicles like ours are subject to fouling and poor fuel atomization which to varying degrees can also affect fuel economy. but if you have been using good fuel and have already run techroline through it then I wouldn't expect much of an improvement by having them cleaned. But it will probably help a little.

Check the Vf voltage at the diagnostic connector while you are at idle and cruising. It should be around 2.5V If it is about 5V then something is wrong telling the ecm to add more fuel.
 

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94SRUNNER said:
Well I never got around to checking the EGR and I have to go out of town for a week for work therefore won't get to work on it any this week, maybe a little on the weekend. We shall see.

If anyone else has any suggestions or thoughts on the matter I would really appreciate it.
Lots of city miles combined with low octane fuel & no Techtron fuel additive (cleaner) creates excessive throttle body carbon build up (gunk) so throttle body must be cleaned.

To clean the throttle body remove the air intake hose and examine the intake and throttle body for excessive carbon build up if found then buy a can of throttle body cleaner labeled "safe on oxygen sensors,TPS's and catalytic converters" do not use carb cleaner make sure your engine is fully warmed up prior to using as when the throttle body is hot it dissolves the carbon easily and quickly.

The labels usually specify to park the vehicle at ground level (0 degrees,no inclination) and have the engine running but I disagree I instead park the vehicle on a hill facing down and shut the engine off and hold a rag below the lip of the throttle body and poor the stuff and use a tooth brush.You can also use "Sea Foam" the best engine cleaner:

http://www.seafoamsales.com

available in Canada through UAP/NAPA Auto Parts Stores.

Sidney® ™
Repairs tv's,vcr's,home/car audio out of my home
E-mail:[email protected]
Dartmouth,Nova Scotia
Canada
1985 Toyota 4-Runner,solid front straight axle,factory cruise control,sunroof,22R-E,W56,RN60LV-MSEK,253 000 KM

:kingme: for I am :canada:
 

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Discussion Starter · #16 ·
Hi Guys,
Well I have an update regard my fuel mileage concerns. A few weeks ago a installed a new fuel filter and dumped a can of seafoam into the intake manifold and let her blow smoke for a while. After several tanks of gas the gas mileage has really improved city/highway combined is around 25-28mpg. All in all I am really happy.

I am going to do a second seafoam treatment when I get a chance, we'll have to wait and see if that does anything.

Just thought I pass along the update!
 

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Discussion Starter · #18 ·
Already did that
 
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