Hey everyone,
I'm new to the forum. I just bought a 1991 F250 XLT Supercab 5.8L, 5 speed, 4x4. It has roughly 91376 miles on it. The speedometer and odometer stopped working fairly recently so it's roughly that mileage. I took it to get an emissions today and failed pretty bad on the Hydrocarbons. What I find kind of odd is that the lower RPM reading is higher than the HIGH RPM reading. Below are my results;

High Speed RPM = 2324
Reading Limit
HC 1772 400
CO 0.65 3.00
CO2 12.9
O2 2.50

Low Speed RPM = 0835
Reading Limit
HC 3099 400
CO 3.75 4.00
CO2 12.9
O2 2.50

From the research I've done, I've gathered that High hydrocarbons can be caused by faulty ignition system/components, leaking vacuum lines, off engine timing, and catalytic converter failure. I know that the spark plugs, spark wires, and distributor cap have been replaced very recently. They look very new in the truck (also the previous owner informed me he had it done). So I don't think it's that. I intend on checking and adjusting the timing. I'm gonna check the vacuum lines using the starting fluid spray method as well as use a hand vacuum pump to check any I can't verify with the starting fluid spray.

I also want to add that it does smell like it is a bit rich in the fuel/air mixture. The smell of gas is quite apparent. When driving it, I have no issues. And as soon as I pulled into the emissions place the check engine light came on. I read a tutorial in a forum on how to pull codes from this generation of trucks. Below is the link. Any suggestions/tips on this?

Code Reader..... - 80-96 Ford Bronco - Ford Bronco Zone Early Bronco Classic FullSize Broncos

I was hoping I can get some feedback and more suggestions from members here. This is my first Ford ever. First truck for that matter. So some help from experienced folks would be greatly appreciated.

Thanks yall!

 

I didn't read through the link. Are you needing some clarification on the procedure? When my truck failed emissions, I performed the KOEO and ER test, and it displayed a fault code even though I didn't trigger a CEL. In my case, it was a fault in with one of the AIR solenoids. Replaced it and ran another self test with no codes displayed. Passed emissions test, but at a different station.

Look through this post https://www.ford-trucks.com/forums/9...em-solved.html where you will find a somewhat detailed discription of my procedure.

 

The truck may have 191k on it or more, the odometer is only a 5 digit read out. If the smell of gas is obvious, then you probably have an issue. Pull the codes and come back with the results and we can likely help you out. Not too much we can do before that. I wouldn't bother checking anything else until that is done.