Our Community is 705,000 Strong. Join Us.


What makes a Car run lean?


happydog500
03-14-2010, 06:04 PM
I've posted here about my car. When I give it a little throttle, it seems to pick up OK. If I'm driving down the road, floor it, the RPM's go up, but the car doesn't gain much speed. The description sounds like clutch slipping, but doesn't feel anything like it.

A man at the dealer told me that's a classic fuel filter symptom. You give it gas, the RPM's go up but it's starving for fuel. "Classic fuel filter symptom" he said.

I was so happy, an easy fix. Problem is it didn't fix it after I changed the filter. What else can cause a lean or starving for fuel without triggering a code? Fuel filter is less then a year old. O2 Sensor from the dealer a year a go. No codes.

Thank you,
Chris.

MagicRat
03-14-2010, 06:44 PM
Was this loss of power gradual, or happen suddenly?

Ideas??

Blocked air filter,

low fuel pressure (bad pump or regulator... test for fuel pressure)

Loose cam timing chain that has skipped a tooth.

Worn camshaft

Mickey#1
03-14-2010, 07:44 PM
It should throw a code if it's running lean. How many miles on the catalytic convertor?

MagicRat
03-14-2010, 07:48 PM
It should throw a code if it's running lean. How many miles on the catalytic convertor?

Whoops, yes I forgot about a plugged cat. I once had a Ford F350 with a 5.7 that behaved exactly the same until the cat was replaced.

HotZ28
03-14-2010, 10:50 PM
Whoops, yes I forgot about a plugged cat. I once had a Ford F350 with a 5.7 that behaved exactly the same until the cat was replaced.I think he has had some advice about the cat in a previous thread, Click Here (http://www.automotiveforums.com/vbulletin/showthread.php?t=967709) maybe he replaced it??????

happydog500
03-15-2010, 09:46 PM
Sorry, I didn't get a message notifying of answers.

I had the cat checked and it is good. Can't remember but I think he said 3lbs.

HotZ28
03-15-2010, 11:28 PM
I had the cat checked and it is good. Can't remember but I think he said 3lbs.What rpm was the 3 lbs?

happydog500
03-15-2010, 11:52 PM
I don't know. I was at an exhaust shop. He had it up on a lift and a guy was revving it up with the owner sticking a prob like thing before, after the cat and, the muffler. After he was done, he welded (like) the wholes, and told me the cat was OK, I think he said it's about 3lbs.
Chris.

Mickey#1
03-16-2010, 09:37 AM
I'd check the fuel pressure & get a scan of the long & short term fuel trims. Have you checked for vacuum leaks?

happydog500
03-16-2010, 11:13 PM
I've had two different fuel pumps with this motor. Both had no effect on the performance with this problem.

I can check for vaccume problems. Don't see any off hand. Thank you for the post.

Chris.

happydog500
04-28-2010, 12:47 PM
The Mechanic I use finally got caught up (Kind of).

When I went back in, I described the problem. He asked if it seemed like when it kicks down, it's going down to far, like in a lower gear.

Yes, it's like if I was in 3rd, floor it, instead of going to 2nd, it would go down to 1st. Or, if on the freeway, it wold go from 4, not to 3rd, but to 2nd.

But on the other hand, when I start out from a dead stop (with full throttle), it doesn't accelerate like it should, so it can't be in the wrong gear.

He told me it might be a "line adjustment". I should take it in to a trans shop, have the guy see if he could adjust the linkage or transmission.

I took it in. The trans guy said there is no adjustment on these trans. It's all controlled by the computer.

We went out for a test drive. Didn't seem like his 20 years in the trans business he learn very much.

When he had it in OD, it did the common problem with the valve body, of seeming like a misfire, but it's not. It's not even in the motor, but the trans. This is not the problem I'm wanting fixed. When we got back, he put the car in drive, put his foot on the brake and gave it more and more gas. It was so much I was thinking, 'what the hell are you doing, stop!'

He let off, then did it again and again. He said he was doing it to sow me it was the motor misfiring. Of course, he couldn't get the motor to misfire.

After that, now when I get into the car, put it in reverse, I hear a big "cluck" and it goes in like a sledge hammer hitting. When I put it in drive, it does the same thing.

I have been trying to figure out what could be wrong with the motor. After all this time, I switched to it may be in the transmission. I spent a day thinking it was in the transmission. Now I have a clunking transmission. When I woke up this morning, thinking of all this. I realize, I changed the motor. The transmission is the same. How can it be in the transmission, if it started when I only changed the motor?

Plus, like I said, if I start out from a stop and floor it, it isn't accelerating like it should right off the start.

The trans shop said he would have to have it for a day and do a complete diagnoses on it.

I also found out if I drive mostly on highway, and just a little city, I'm at 18mpg.

I'm now in a worse situation. The same problem, no good acceleration and, 18mpg - with a clunking transmission.

Chris.

happydog500
05-04-2010, 12:32 PM
Just got back from a trip. Went over two mountain passes. Coming back up the last long, big hill, I got a CEL. I had it checked and it was "101" - MAF.

Wonder if this could be the problem? It has been acting up for a year before the CEL, so I'm thinking if the problem is the MAF Sensor, it would of triggered a code a long time a go.

I found on this trip, the mileage went up from 18 to 26mpg.

Thank you for any input,

Chris.

Add your comment to this topic!