I have an 89 tbi v6 swb truck. I took it to get it inspected for the first time since I owned it. It failed miserably and the guy suggested a tune-up and a new catalytic converter. So I did a tune up, catalytic converter, and changed the map sensor hose because it looked rotted. Checked for vacuum leaks and haven't found any.

Took it back and it passed the HC and the NOx with flying colors with the new cat!... Failed the CO% though. I was wondering if anybody had any experience with this.

From what I have read it seems to be running rich to fail co% which would explain the poor gas mileage, but I thought changing the map sensor hose would have fixed that.

what should i try? bigger air cleaner? msd coil? new 02 sensor? all the above?

CO% standard-2.51 actual-25 mph(rpm1336) 5.86 15mph (rpm1355) 7.11

FAIL.

 

i would guess that with as old as the truck is it might need a new o2 sensor if you have not replaced it. you can order a ntk o2 sensor from rockauto.com for cheap if they are expensive locally. these truck like the ntk brand o2 sensor best. also how old is the air filter? a dirty air filter could cause it to not burn as clean as it should. also did you bring the truck in hot? when going into emission testing you should bring your truck to the emission testing place as hot as you can so it will be burning nice and clean. a good run down the highway to get it hot is usually the best way to do it.

 

Is your truck missing at all? Mine does under certain conditions, which include conditions relevant to an emissions test. I usually end up with a waiver. I think I have a bad valve or spring. Its not a tune-up or 02 or MAP sensor issue in my case. What did help was retarding the timing a lot. That and actually unbelting the smog pump (can't pass visuals, but ran still run it as a diagnostic test). Lol

 

@crazzywolfie I'll go ahead and replace the o2 sensor, Ill be sure to pickup an ntk. The o2 is original and all, so It couldn't hurt. The air filter is a new one, but in the stock airfilter box, I was wondering if an open element would work better? I made sure I had everything heated up nice before I made it to the inspection place, so that wasnt the case.


@wontacceptthis Its not misfiring under any condition.


Ill get a vacuum reading at idle and check the fuel pressure to make sure the return is working. gas mileage sucks btw. I got less than 120 miles to a full tank. wtf.

 

i think an open element air cleaner would definitely help it by not restricting how much air it could breath in but i don't think it could help that much. if you can only go about 120 miles per tank of gas you must be dumping it out the tail pipe. i know even at 9mpg you should at least get 200 miles out of a tank of gas. i would guess if the old o2 sensor is giving the computer incorrect readings it could explain why it is allowing fuel to be dumped out the tail pipe.

 

You could try unplugging the o2 sensor, and the truck should stay in closed loop mode. That should make it run closer to normal than whatever you have going on thats getting you 5 mpg . . . providing the o2 sensor is the problem.

 

I think Im going to just park it till I get my check later this week and find some time to fix it correctly. I really don't want to ruin this new cat converter. Ill post my findings when I tear into it again.

It has a new coolant sensor, both of them.

Is there a volts meter test I can do on the map, tps and o2 sensor to get an idea of their condition?

Maybe I should look at the pressure regulator vacuum line? I got a v8 360 tbi unit with new injectors in it and all the other sensors on it, are they compatible?

 

Okay. So I've put new plugs, plug wires, cap, rotor, msd blaster 2 coil, 14" air cleaner, and a new o2 sensor. The old 02 sensor ports were clogged.

I can still taste fuel while its idling. The injectors just look like they are spraying too much at idle, and it does load up and bog when you rev up and down on it. I have v8 tb, map, tps, and injectors to swap in if they are compatible? maybe I'll check rock auto part numbers to figure that out.


I'm going to check to fuel pressure tomarro. I cant find my damn vacuum gauges. Had 4 of them to sync the carburetors on my motorcycle. Nowhere to be found.... What should the fuel pressure be regulated around? 15 PSI?

Is there a procedure to check the TPS and MAP sensor? By voltage? I couldn't find a haynes for the truck at either parts store I went to.

 

i would guess the tb off the 360 would have bigger injectors in it to feed the thirsty 360. i know rock auto show different injectors for all there TBI engines. could maybe check the timing.

 

Just went through part numbers. The TPS, MAP and fuel pressure regulator are the same number. Ill try swapping them. Only code 55. I'll check the timing when I get ahold of a timing gun. Thanks.