Any Auto Mechanics Here?

[Rcpilot]

I need help with my truck. My fuel mileage went from about 21mpg down to about 12mpg. This happened over a short period of time--about 6 weeks of slowly worse and worse running. It did not happen suddenly--so I don't think that the timing chain jumped a tooth.

1994 Nissan truck
2.4L KA24E engine. 4cyl
170,000 miles

It idles real rough. My fuel mileage went down to less than 1/2 what it should be. It runs okay, but the idle is awful. shaking the whole engine and truck. When it is cold, it runs. When it starts to warm up a bit, there is a period of time when it wants to die when I let off the gas pedal. I have to use gas and brake at the same time to keep it from dieing. After it warms up to temp, it idles real high (1500RPM) but it won't die anymore.

I changed the plugs. They were worn, but none of them was fouled. All had the same burn characteristics. Light tan color, just as it should be. About 40,000 miles on these plugs. The gap was worn to about .060" so, I knew they were worn, but they still looked good. I installed new plugs and gapped to spec at .044"

That didn't change anything. Still rough idle.

So, I pulled the air filter out. It's a little dirty, but not clogged. I took it completely out and wanted to see if that was causing the problem. No change. Still rough idle without an air filter. Put it back on.

Pulled the distributor cap to check the cap and rotor. Looks a little bit worn, but no carbon build up or flash anywhere. About 40,000 miles on this cap and rotor. Looks fine, so I put it back on.

Went outside at midnight and drove to a dark parking lot. Popped the hood and looked for arching plug wires. Don't see any voltage jumping around. Don't hear any of the tell-tale popping sound from bad plug wires. About 40,000 miles on these wires. Good high quality Beldon wires. Thats not the problem.

Okay, so not the plugs, wires, rotor, cap or air filter.

I'm thinking it could be a sensor. This truck has 4 sensors
Throttle position
Ambient air temp
Mass airflow
Oxygen sensor

BUT:
I called the dealership and they said that if it was a sensor, then I'd see a CHECK ENGINE light on my dash panel. I don't see one. I know they all work, because they light up when you turn on the key. They go out when you start the truck.

The dealer said that if I have no CHECK ENGINE light, then it's not a sensor. He said it may be a clogged injector.

My friend is a mechanic at the power company (Excel Energy) and he is a top AAA certified mechanic. I called to pick his brain, but he's one of those guys who can't reason through a problem and use logic to figure it out. He says to hook it up to a computer and get it diagnosed. Rolling Eyes


I went to 3 different auto parts stores and they have the diagnostic computers, but they only go back to 1996. My truck is a 1994.

I don't want to take it to a shop. It'll cost me $150--$200 just to get it hooked up to a computer and diagnosed. Add the cost of the parts, and it could be a $400-$500 bill. Can't afford that.

Can anybody offer any help? I'm out of work right now and I don't have a ton of money. I need to get it fixed because I'm wasting gas @ $3/gallon. It's costing me money. Money that I could be using for food and job searches.

Thanks

[wonderloss]

A clogged injector is a possibility. Have you tried running a fuel injector cleaner through it?

I also had a similar problem in a much older car when I had a valve sticking.

I am far from an expert, but these have helped with similar problems in the past.

[goldenmean]

Im no mechanic but I think you should call into NPR's Car Talk

Car Talk

FAQ #1: What's the 800 number for the radio show?888 CAR TALK. For the alphanumerically challenged, that's 888-227-8255. Listeners outside the U.S. should call 617-353-6350.

FAQ #2: When is the show actually broadcast? I've heard it at different times in different cities.

Car Talk uses voice mail to be fair to people in all the different time zones. Anyone can call anytime they like and leave a message. Every week our Associate Producer Louie Cronin and her staff of lackeys go through the messages and pick a variety to throw at the guys when they go on the air.

[bigbratt]

check the fuel filter it may be that.

[heels92]

I grew up in a garage, sounds to me like you have something going on with your fuel system. Clogged fuel injector(s), bad spark plug(s), airfilter, or a combination of all the above. When is the last time you had it serviced?

If it is running bad at idle, that would also point to these above, but a good servicing would probably fix this without spending an arm and a leg...

Darrell

[Frankie]

I love car talk Jeff!
It sounds to me either fuel injectors or a vacuum leak. If it is the fuel injectors you will need them to be replaced. Cleaning them with that kind of mileage is futile.
Check all of the vacuum lines. With that many miles hoses dry out and split. Check the seams also. If a seam split you might not even notice it from a visual. You need to bend them to see it.

[Rcpilot]

I sprayed ether around my intake manifold and vacuum hoses. No change in idle speed, so that tells me it's go no leaks.

I did find a product called BG 44K. It's a fuel injector cleaner and it supposed to be the best thing for a clogged injector. I put a can in my tank and the topped off the tank with mid-grade fuel. I'll have to run that tank out and see if it helped. Injectors for this truck are NOT cheap. About $100 each.

I'm also going to check the EGR valve. Been told this may cause the problems I described.

I don't think it's my plugs, wires, cap rotor. Replaced the plugs and everything else looks good. Only about 40,000 miles on that stuff.

This truck has been a solid vehicle for me. I've only had this problem one other time, and it just needed the usual cap, rotor, plugs and wires. That fixed it right up. But, that was when she had about 125,000 miles on her and I had simply let the tune up stuff go too long.

This time around, I'm baffled. I love car talk too!! Tom and Ray are hilarious!! I listen every Saturday.

[funkpolice]

could be a crank sensor.

[CATALYST]

Anything leaking on the ground under the car? Smell anything different? Is the exhaust a different color? Does it run different on the freeway or is it just at idle?

[Octoman]

Some good suggestions. I would also suspect the PCV valve.

[Frankie]

If a fuel injector is stuck open cleaning it won't fix it. It would also explain all the symptoms.

[Rcpilot]

Originally Posted by Frankie

If a fuel injector is stuck open cleaning it won't fix it. It would also explain all the symptoms.

I'm beginning to think the same thing. The more I think about the problem, it seams like it's an injector thats stuck in the open position. I don't know if cleaning will help or not. Too late, I already added 44K to the tank.

[Frankie]

Good luck! Just pray it's not the wire harness sending a constant electrical current to the injector. If so then the whole harness needs to be replaced and the harness could cost as much as that truck.

[JWarren]

If you are smelling a strong gas smell coming from the exhaust pipe while in idle, it is possibly the Heated O2 sensor in the exhaust pipe. This is the sensor that controls your rich/lean fual flow.

Your symptoms are just like my F150, it's doing the same thing and it is the O2 sensor. My problem is locating one for my 87.