Very rich fuel mix

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Very rich fuel mix

March 17, 2005, 03:54:53 AM

New Cat owner and new to the Forum. Please help...I just bought the 87 cat with 3.8 with throttle body. It has been sitting for quite a long time, or very minimal driving. I have replaced plugs, wires, dist cap, rotor button and ran codes at Autozone. The only code I had was for EGR valve and/or sensor (31), and given that it has been sitting, I just replaced them both. Idle seemed to improve a little to begin with, but still not right, and possibly getting worse. 'Engine' light stays on at start-up for about 15 minutes. Ran codes again and system passed. I am tied to emissions testing and and failed due to high hydrocarbons and high CO. They suggested running full tank of gas with injector cleaner, and told me to run the heck out of it. Can't notice improvements at all. I can detect fuel odor at exhaust, and getting TERRIBLE MPG. Any thoughts as to where to start next would be greatly appreciated.

Re: Very rich fuel mix

Reply #1 – March 17, 2005, 01:01:52 PM

Have you verified your timing is correct? Is the fuel pressure correct? I'd definitely replace the fuel filter. Can you quantify "TERRIBLE" gas mileage and the driving conditions under which they were achieved? Also, are there any drivability problems? i.e poor idle, bucking, hesitation, etc.

Re: Very rich fuel mix

Reply #2 – March 17, 2005, 02:12:45 PM

You may want to talk to jcassity about this, he knows the system inside and out and helped me out w/ a v8 throttle body swap on my 87 3.8 bird. It may have something to do with your fuel pressure regulator (that gold thingie behind the injectors).

Re: Very rich fuel mix

Reply #3 – March 17, 2005, 04:15:20 PM

ok when u did that tune up did u change the o2 sensor? if not and its origional maybe that could cause your bad fuel milage. also your fpr could of gone bad on you. when the car is running pull the vacume line off the fpr if its wet with gas then replace the fpr. and definatly that o2 sensor if u havent already. that will help with gas milage.

Re: Very rich fuel mix

Reply #4 – March 17, 2005, 04:26:50 PM

Hey Amooset, Yougot that 5.0 CFI on? how's it runnin?

Re: Very rich fuel mix

Reply #5 – March 17, 2005, 04:33:19 PM

Quote from: Cougar8775

also your fpr could of gone bad on you. when the car is running pull the vacume line off the fpr if its wet with gas then replace the fpr.

His fuel pressure regulator does not connect to vacuum.

Re: Very rich fuel mix

Reply #6 – March 17, 2005, 04:35:49 PM

i must be thinkin of the gm fpr's

Re: Very rich fuel mix

Reply #7 – March 17, 2005, 04:40:15 PM

Quote from: Cougar8775

i must be thinkin of the gm fpr's

I believe all non-CFI fuel injection Ford engines used FPRs with a vacuum source.

Re: Very rich fuel mix

Reply #8 – March 17, 2005, 05:49:11 PM

I appreciate all of the posts. I was told the fuel pump and filters were new, replaced just before I bought it. I haven't changed the O2 sensors but had decided this was probably a good idea. I have read through a lot of threads from everyone's previous posts but don't remember much being said about the regulator. I will check this out tonight.
:D :D :D
Thanks again to all... :D
Dave

Re: Very rich fuel mix

Reply #9 – March 17, 2005, 05:51:34 PM

I haven't verified timing yet either so I'll add this to the list also.

Thanks...

Re: Very rich fuel mix

Reply #10 – March 17, 2005, 06:16:21 PM

The idle is rough, especially to begin with, and will die most of the time. I have to keep a little pressure on the pedal at first.

The service light stays on for first 15 minutes, and idle seems to get better about the same time it goes out.

JeremyB, I drive 35 miles to work (all interstate) and I have used nearly full tank for about 180 miles travel. Granted, I was leaning in the take-off heavy to 'blow it out', but it is blowing fuel through the exhaust pipe as well. Fuel smell from exhaust is pretty strong when idling.

Re: Very rich fuel mix

Reply #11 – March 17, 2005, 07:13:29 PM

Quote from: 87 3.8 CAT

The service light stays on for first 15 minutes, and idle seems to get better about the same time it goes out.

The service light going out and idle improvement are coincidences or your imagination. The service light is not the same thing as the check engine light and for all intents and purposes is useless. It can be reset by pressing and holding down the trip and trip reset buttons simultaneously.

It is odd your engine is running so poorly and isn't setting any codes. Blowing fuel through the exhaust could be a symptom of a leaky fuel injector. It could be many things. Does the car's behavior get better or worse when it gets to closed loop operation? That should occur about 3-10 minutes after you crank the car.

I would check the timing, fuel pressure regulator, and the injectors for leaks before moving on to other things.

Re: Very rich fuel mix

Reply #12 – March 17, 2005, 08:39:29 PM

It seems to get better, at least most of the time, but takes awhile. I have driven it all interstate this week, and by the time I get to work, it is idling pretty steady, shifting smoother, and seems to be 'happy'. It likes the long run better, and doesn't seem to adjust with short drive (4 or 5 miles).

Looking back through the threads, I can find favorite settings for timing but don't see anything to help me understand exactly how to check / adjust it. Suggestions??

There are no obvious leaks anywhere around the throttle body area, and I can't find any vacuum leaks, but these are about things I have tried.

Re: Very rich fuel mix

Reply #13 – March 17, 2005, 09:00:10 PM

Took care of the light. Thanks...

Re: Very rich fuel mix

Reply #14 – March 17, 2005, 09:17:34 PM

Quote from: 87 3.8 CAT

I can find favorite settings for timing but don't see anything to help me understand exactly how to check / adjust it. Suggestions??

This write-up should be good enough. Sometimes you have to clean the harmonic balancer and paint the marks to see it with the timing light. The #1 cylinder on the 3.8 is the same as the 5.0.