I just took my 89 351w 4x4 with c6 transmission truck on a small road trip this weekend. I checked mpg for the trip which was all highway @ 70 mph and averaged around 10 mpg. I don't think that's what I should be getting, so I checked for codes tonight. I counted a 23 and then a 33 in the memory. The truck drives great, plenty of power, idles strong but high, around 1000 RPM.

Looking online I found that the 23 says the TPS is out of range. Is it time to fork out $35 for a new one? The 33 seems to be EGR related, but not sure where to go from here. I read the other EGR thread but my truck doesn't have any of the bad side effects described there.

 

You will have to go through the tests that aliens8mycow has done to check the EGR. Fixing it will help gas mileage. You can test and if needed adjust the TPS before replacing it.

 

how do I test and when do I know the TPS is correct?

 

Probe the ground and signal wire. Turn the key on (engine not running). The sensor should read 0.50 to 1.0 volts closed and 4.0 to 5.0 fully open.

 

thanks, that sounds easy enough, I'll check it out tonight before buying a new one. The voltages you listed have a range, if I were to adjust it to the lower or higher side of that range will it make the truck run lean or rich? Or will the rest of the system learn the calibration and run the way it wants to run?

I did unplug the TPS and the truck wouldn't idle smootly, so I think it's working, just needs adjusting.

 

I'm not sure if it gets you into a rich/lean situation, but they say that 0.98v is the sweet spot.

 

.98v+ is on the lean side of 14.7:1 ratio and closer to Ping city.

 

I think I'm so far from lean city right now... my exhaust smells rich when I run. There's also an exhaust leak, I'm going to run it by a muffler shop today.

It poured down rain all evening yesterday, so instead of working outside on the truck, I worked inside on the scooter. I'll attack the truck tonight if all goes well.

 

A's8C set his adventures w/ error code#33 aside for the moment and currently is doing battle w/ the most diabolical of all Injectors of fuel, "#3". Tune in to his thread later today where he should be able to easily pass the 20 pages of posts for a single subject milestone and continues to demonstrate a level of dedication & determination I haven't seen since the neighbors pit bull decided to make the new Mailman his favorite chew toy! Anyway, depending on which code def. book used as referance, #33 is EGR failure, or my personal fav,"EGR fails to close properly. Which can occure when carbon buildup does not allow the inner piston from seating properly. You could remove it and clean out the flow restrictions w/a solvent while working the valve w/fingers to insure valve seats & seals as this is a normally closed valve. If it doesn't, the return spring has worn out. If it does seat & seal, check it's diaphragm for leakage and reinstall. Next suspect would be the EGR position sensor itself(there's more than one resistance version & color coded) These have a rather low failure rate as do most of the sensors & many times mimic failure due to poor connection quality(Including where their circuit connects to ground. The cheapest way to deal w/ them is go to a pick your part junkyard and pull 2 or three off their trucks. They'll cost you 2 or 3 bucks each & I've yet to bring home 1 dud. If you clear your codes and your compression is fairly ballanced , if your O2 sensor has 30k or so, replace it. If newer or in the mean time, remove it & douche it w/electronic contact cleaner & reinstall.There will be some improvement. However, obd I systems are limited by use of MAP rather than MAF sensors for alot of reasons. Pick up a can of Seafoam & use in air intake as directed to reduce deposits in combustion deposits, always produces a little better idle &throttle response. Stick w/ 87 octane. If you want I can tell you the correct method to increase your initial base timeing but you have to have all the other ducks in a a row first . Most people don't, which is why stock initial timing is detuned to 10 BTDC, right from the factory.

 

I pulled the TPS off to check it and see how to adjust it. I found that there's no adjustment for it at all, I also found that the voltages were about 15% off of what was listed here. I went ahead and got a new one just to be thorough.

About the EGR, I've got an exhaust leak in the air tube going to the cat, so I'm going to fix that before I dig into the EGR more. The parts are currently on order. I already read the first 10 pages of the egr thread. I feel I understand the functionality of that system a lot better now.

I don't think I need to worry about carbon buildup yet because my engine only has about 300 miles on a rebuild. I have no clue when the o2 sensor was ever changed, should I replace it even without a code? What kind of MPG should I be getting? is 15 mpg highway reasonable for a 5.8L truck? I'm nowhere near that now.