3.0 Pings, gets poor fuel economy and backfires

[gorgeman]

I have a 1999 Mazda B3000 (Vulcan 3.0) with 149k on it and have been fighting with a drop in performance, fuel economy and pinging all summer. The engine idles smoothly at 1000rpm (is this high?) and seems to have no real problems until you are going up hill.

Between 2-3k rpm the engine knocks like crazy, especially on a hot day after the engine has warmed up. Additionally it backfires when it's hot if I rev to 4000rpm and then let the gas off quickly. It will also backfire when engine braking at 3500 to 4500 rpm.

The fuel economy is terrible. At one time I used to get 23mpg in this vehicle (65mph in Colorado high country) and now I live a sea level and get 17mpg on the highway and 15mpg in town! Pretty crippling with todays gas prices.

I have taken it to a number of mechanics and have replaced the DPFE sensor, mass air sensor, coil pack, and plug wires. The two O2 sensors upstream of the cat have only 30k on them and the plugs have 20k. The Ford dealer wanted me to spend $1600 on a new ECM, a fuel system revamp, and a disassembly of the engine for decarbonizing. It sure seemed excessive when a used engine isn't much more expensive.

Has anybody else ever seen this kind of thing in 3.0L Ranger before? Do I really need a new engine/total engine overhaul at only 150k? Got any ideas of what I could replace next (haha)?

Thanks for your help,
Seth

 

[fastpakr]

This sounds like a simple vacuum leak.

 

[Wicked_Sludge]

my escort acted a lot like that before i discovered the timing belt was 4 teeth off. it also makes me think of an EGR problem...

 

[gorgeman]

Could it be an exhaust leak? Poking around last night I found a leak where the exhaust header connects to the y-pipe (terminology?) on the driver's side (side with the EGR). This is upstream of the 1st O2 sensor and the cat, so I thought that it might screw with the O2 reading and cause an "incorrect correction".

Does anybody know about this part of the system? As you might be able to tell from my posts, I know just enough to be dangerous and have fun, but the real mechanic stuff (anything requiring a tuned ear or hand) I need a bit of help with...

Thanks to those who have read and replied to my post so far.

Cheers,
Seth

PS, I thought timing too, but being a Vulcan, it has push rods.

 

[dogboy]

The exhaust leak sound like a logical cause to me. If the o2 senseor can't read what is going on with the engine it could send wierd readings and making things do screwy things like dump in more fuel right? Accounting for you fuel problem. Just my thinking though.

 

[Wicked_Sludge]

having pushrods has nothing to do with it. you still have a timing chain and a cam. it wouldnt be the first time a timing chain jumped a tooth, causing the valve (and possibly ignition) timing to be off.

i'd say the chances of your exhaust leak causing the problem are slim. the o2's really only have enough effect on the system to cause it to get bad mileage, not cause the serious driveability problems your having. if you want to check it out, unplug the sensor and see if the truck runs better (it'll throw a CEL and go into open loop, ignoring that sensor).

 

[gorgeman]

Thanks Wicked Sludge, I'll give that a try. That said, I got the exhaust leak closed up today and initially the truck seems to drive better. I will put a tank of gas through it and see what happens. If it was the exhaust leak, should I unplug the battery to reset the fuel trim?

 

[94 splash]

i was having the same problem and it turned out to be a bad intake manifold gasket ... and it was causing it to run rough and also messed with the idol if thats another problem you have.. just another idea

 

[Wicked_Sludge]

unhooking your battery will accomplish nothing.

if the CEL came on at any point, clear those with a computer and then leave it be.

 

[captainphoton]

Smoking

I have a 2002 V6 ranger that was smoking and using alot of oil, I placed a white piece of paper over the tail pipe it was covered in soot in seconds.
When I was replacing the PCV valve I noticed the rubber grommett in fits into was not snug. I guess over time heat had shrunk and I was getting a vacuum leak into the crank case. I replaced the grommett and could feel the difference I now have a good seal, another test with piece of white paper over the tailpipe This time it came back clean, now I am not loosing oil and my gas mileage got a whole lot better.

 

[JohnnyO]

149k is a lot of miles but a properly maintained 3.0 is good for more. Mine wasn't as bad as yours, but I had a 99 3.0 Ranger that I bought new, only problem was that it knocked and ran like crap on the summer blend of gas we get here. Had it to the dealer a bunch of times but the only real cure was to run 89 octane or higher in the summer.

 

[gsxrken]

When my 99 manual 3.0 4WD was new, it pinged like mad. I brought it back, and the dealer said there was a new computer tune that would eliminate that. It did, but it also took away what little balls the truck did have. Watch out for that "fix".