I have a 90 BII 4x4,2.9 automatic.The problem is that it idles very rich,even after it gets hot.I have checked and no codes.I have replaced the O2 sensor,map sensor,fuel pressure regulator,and even put in new plugs.Problem is still there. Any ideas?

 

Maybe your thermostat is sticking open. I had this condition once and it tricks the computer into running rich some how. Does your gauge read in the middle of the Hot Cold range? Don't forget your PCV valve too.

 

I have changed thermostats,and replaced pcv vavle some time back.Gauge reads in the normal range.

 

You may have to start running pin point tests on the sensors. There is a temperature sensor on the intake that can be checked. Use the procedures in like a Hayne's manual to check it. What is your MPG? If it is around 17-18 city you are not too rich. How does the truck run? The more info you give, maybe it will click with someone who had a similar experience. LOL

 

The gas mileage is'nt good.I get around 12 miles per gallon,but thats on short runs.I don't usually go very long distances.Also I'm running 33 inch tires,so I expect my mileage to suffer some. I have also noticed that on initial start up,say when its pretty cold outside,the truck idles high for awhile then cuts down to normal after awhile like its supposed to.But when the outside temp is moderate it doesnt rev up much and idles rough until it warms up.

 

[QUOTE=shiloh66]I have a 90 BII 4x4,2.9 automatic.The problem is that it idles very rich,even after it gets hot.I have checked and no codes

what do you mean by that do you get any codes? you must get pass codes
if you don't get you have problems there and must be resolved first.

running rich can be quite of few things but wasting money on sensors that you don't need to change . one question do you have striaght pipe for exhuast or do you have your cats still in place. when was the last time you did engine timing

how does a thermostat change your rich problem ? it doesn't
but it does cool the engine and the sensors .

 

I had a thermostat stuck open and it took the truck longer to warm up. It ran rich, because I noticed that my oil was being deluted by raw gas getting by the rings I guess. The new thermostat instantly cured the problem and now I can run my oil changes back to 3k intervals. This was over 60K miles ago and it has run like a top ever since, with regular maintenance.

Shilo, larger tires will impact your MPG in several ways, some you alread have guessed. However your odometer reading will indicate fewer miles than you have actually driven. You can sometimes change out the spedo gearing to compensate, however my B2 was at its max gearing on the spedometer. I had to calculate the difference, using the difference in tire diameters. For instance my B2 came with 205 75 R15 tires. I now run 235 75 15 tires so I have to add .08% to my odometer reading to be accurate, also my speed is off logerithmically so at 60MPH indicated I'm actually doing 64.5 MPH, important to know if you want to avoid speeding. I think there are web sites where you can plug in your tire sizes before and after and it will tell you the difference. Ever hear of The Ranger Station, I think they have one.

Good luck,
Tim