Explaination needed. My 99 4.0l auto has a rich smelling exhaust smell. I am not getting a check engine light on and even tested for codes. Everything has a 'test passed'. I am also getting a hesitation as if it is either choking for gas or getting too much gas. When the hesitation starts I do get a strong gas smell. When I come to a stop during the hesitation, the truck bucks a little. I shut off the truck, turn it back over and the hesitation is gone, well until it decides to act up again. I have cleaned the maf sensor, new plugs, new fuel filter new air filter. Have had the Dealership do 3 seperate diagnostics which have all come up normal. I do not want to just start changing out sensors if they're not fouled. Could this be fuel injectors? I have run injector cleaner every other tankfull for the last month ( that is a fill up three times a week since I am only getting 14/15 mpg). Please help! Txs

 

Well, you have reach exaust but HEGO reads normal mixture. May be o2 sensor is bad, may be you have exaust leak and exaust is mixed with air.

 

I have considered the O2 sensors. My warranty covers the sensors, but without a code showing the bad sensor, I would be stuck with the cost of replacing. I have three and at almost $80 a piece I am not looking forward to absorbing that cost if they are not faulty. I could have the manifold looked at to determine if I have an air leak, but dont think I have a leak. Thanks - C

 

in my 200 3.4 tacoma i had, the only part i had to replace for the 165k i owned it, was an air fuel sensor. my mpg went from about 20 to about 6 or 8, was pi$$ing straight fuel out the pipe.

i dont even know if the ranger has one or not or the coorelation of an air fuel sensor vs. o2 sensor.

but my air fuel sensor an OEM part from yota was $270 bucks.

 

The mpg you posted sure suggests to me that the air/fuel ratio is running rich.

Interesting that the Dealers 3 diagnostcs scans didn't turn up anything.

So I'll brainstorm a little & toss out some things for consideration.

Seeing as how it sure seems to be an overly rich air/fuel mixture, from your mpg figures, lets think about how unmetered fuel could get into the engine & the computer not sense it?????

My first thought was maybe the fuel rail damper's diaphragm it leaking fuel into it's attached vacuum line.

So stop & pull the vacuum line when it goes into one of it's bucking fits & see if the vacuum line is wet with fuel.

The other thought I had is, maybe the o2 sensors just down stream of the engine, are "lazy" & not responding to changes in O2 levels quickly enough, to keep the A/F ratio in range. But you would think the Dealer would have spotted this by now, with 3 diagnostic scans, but then maybe he's lazy too!!!!! lol

How did the old spark plugs read???? What sort of deposits were on the insides????? This "reading" of the plugs could suggest if we are on the right track, to suspect a rich mixture!!!!

I'd maybe do a fuel pressure test, just for grins, to see if maybe the fuel pressure regulator is intemittently acting out.

On Edit: Forgot to mention maybe leaking fuel injectors, kinda goes along with a fuel pressure problem, but if the injectors are dirty, or have a runny nose, they'll dribble unmetered fuel.

Just some thoughts for pondering.

Keep us posted on your findings.

 

pawpaw, Thank you greatly for the insight. Definitely food for thought. As far as the plugs go, no deposits on the ends, and they were dry when I removed them. As far as the dealership, yes, they are Lazy. Atleast this gives me other tips to check besides the obvious. Will keep posted on my progress. Thanks again! -C