Hello all,

My '93 EB Bronco (in my sig) has started running rich lately. At least, I think it is running rich. The gas mileage has dropped off considerably. Two fill ups ago it averaged 12.29 mpg, but I filled it up today and it only managed 8.3 mpg. Driving conditions are the same. I also notice the idle wanders from 800 to 1000 rpm, and sometimes will go up to 1,500 and stay there. There is also a strong unburned fuel smell, that is getting so bad, it is starting to make me sick when I drive. I have done a cursory inspection of the under hood area, looking for a cracked or broken vacuum line, but have not found anything. I am partially disabled, so that is about the extent of the troubleshooting I can do. I should also point out that you cannot stand by the tail pipe when the engine is on because the smell is too strong. Oh, and when driving, if you just lightly press on the gas it will stumble before it accelerates, and when at a set speed, it will cough and sputter, like it is not getting enough fuel. Makes no sense to me. It never gets so bad it dies, just barely noticeable, but you can tell it is coughing and sputtering.

I had a major tune up done on it about 6 months ago where the entire ignition system (except coil) was replaced, as well as oil and air filters, PCV valve, and new oil. This has only started happening about 2-3 weeks ago. The mileage is so bad I might as well drive my F350 as it gets about the same (8.1 to 8.2 respectively). I figure it has to be fuel related as the ignition system has been replaced, and the strong smell would indicate a fuel problem I would think. Any help would be appreciated.

Jim

 

Jim, have you done any of the onboard diagnostics? I am not great on any of the new computer stuff, but if you can pull codes I will help all I can. Maybe greystreak92 will pick up on this thread and he can help. From what I have seen he is a very good mechanic. Might try dropping him a pm.

 

You might want to look at your engine temp sensor. My '88 was just doing the same thing and I chased down the entire ignition system no difference. Checked and adjusted the timing no difference. I started to talk to one of the Oriellys counter guys he told me to change the temp sensor so I did and the coughing, bucking, and stutering stopped. Apparently this sensor is what the computer uses to judge how much gas to give the engine, mine was thirty dollars and ten minutes to change. It should be near the thermostat.

 

I know you said you looked for vacuum leaks already, but it really sounds like a vacuum leak to me. If you can pull codes, I would definitely try and do that first, then go from there. The engine temperature sensor could be something to look at also.

I know you said you are partially disabled, but If you are able to reach around somewhat in your engine bay, I would recommend getting a vacuum gauge from O'reillys or Autozone (I think they are about $25). You can pull the vacuum line off of the throttle body (on the passenger side) and plug the gauge in there. If comes with some T adapters and such so that you can keep the vacuum connected. From there, you can read if the vacuum is too low or if anything else is wrong with it. You can also monitor the vacuum under throttle by having someone rev the engine, or by pushing on the throttle switch that's on top of the throttle body. You can reach your hand up under the cover and push it from there.

If you aren't able to do that, another thing you can try that's easier to check for vacuum leaks is to get some carb cleaner. Then, when the engine is COLD, turn it on, and spray carb cleaner around where you suspect a vacuum leak would be. If the idle changes when you spray, that's where you leak is.

 

Engine temperature sensor will not affect engine-ONLY reads temp of coolant. AIR CHARGE SENSOR will tell PCM what the temperature the air is going into the intake hose at the throttle body. SCAN FOR CODES Vacuum leaks will produce LEAN codes.Fuel pressure regulator with fuel in vac hose(BAD regulator) produces RICH codes--- THATS where I would look first-- COMMON PROBLEM (smell oil dipstick)also for rich running engine a bad ACS telling the pcm its 30 below will do the same PCM RICHs up the mixture Regards BLUE

 

My apologies, one thing I forgot to mention is that the CEL light does not come on. I did not check for codes because I assumed there would not be any without a CEL light on. The nearest Pep Boys still scans for cods free, and since it is in the same parking lot as Winco, and I need to get groceries, I can kill two birds with one stone. I do have some Chem tool, I can use to see if there are any vacuum leaks. Thanks all for your suggestions, I'll take it to Pep Boys tomorrow and see what codes it pulls if any. I can check some items around under hood, but I need to use a step stool, or chair, and my right knee does not bend, so it makes it difficult to get to some areas. Also, I am deathly afraid of falling while on the step stool, or chair, and injuring that knee again.

Jim

 

EEC IV will not always set codes-- much harder to diag. OBD II 96 and up you could read the pids at least and read history codes. My money is on fuel pressure regulator or Air Charge Sensor, Vac leak would have high idle (upper intake gasket leaking) lean codes, surging or would hardly idle at all, look for rubber hoses collaped (PCV) hoses or vac caps off, Egr opened,stuck etc regards BLUE

 

only the mass air equiped broncos would have the air temp sensor in the intake/tb area. otherwise its in the lower intake manifold itself.

 

TruBlu there are 2 temp sensors one for the dashboard gauge and one for the EEC module pgs 38 and 82 of the Ford Electrical and Vacuum trouble shooting manual. The same one you used if you worked in a dealership. My Bronco did not come with the mass air sensor. But I am considering replacing the Air Charge Temp sensor only because I know Temp sensors dont last forever. But changing the TWO wire coolant sensor going to the EEC Did stop all of the Symptoms Nighteyez complained of.

 

IMHO...check for codes, intake leaks...which can make the ecm richen up the mixture.

 

Took the Bronco to Pep Boys to have them scan for codes. They told me since it is not OBD II they can't scan for codes. However, they will do a diagnostic for $90. I told them no thanks. I picked up an air temp sensor and fuel pressure regulator while I was there. I will see if I can get them installed tomorrow if I can find out where they go, and I can do the work myself. If not, I'll pay a friend to do them.

Jim

 

90$ to check codes? That sucks. I don't know much about reading codes on OBD I systems, but I have read it isn't too complicated to do it yourself. I know Greystreak knows the technique and apparently you just need a paperclip and your keys or something along those lines. I suppose I'm lucky having OBD II on my bronco.

 

I havent found anybody who has a OBD 1 reader anymore. I bought my reader (OBD1) a while ago and it has paid for itself along with the facory manuals. The thing is sometimes a bad part will throw a code that you have back track to find the bad part.

 

Would a 1990 F350 have OBD I? If so, I bought a reader for my F350, I can use that on the Bronco. However, I talked with my mechanic friend yesterday, and he said he will install the fuel psi regulator and air temp sensor for me. He has a code reader also. If not for OBD I, I can let him use mine if it works with the Bronco.

Jim

 

yes the one you bought for the F350 will work on the bronco.