gas mileage and valve cover gaskets

[87mefull]

I'm still fighting some problems with gas mileage. No codes, no vacumm leaks, and the timing is set at 10btdc.

If my car sits and idles, the gas mileage drops alot. It can drop from 15mpg to 8-9mpg easily and the car starts to run a little rougher (shows this on the tripminder). The only thing I can think of are the valve cover gaskets or the cataytics are the problem. The car has plenty of power, just gas mileage is still bad. They are leaking badly but can oil actually get into the cylinder and foul the plugs? I did remove the plugs before and the threads had oil on them, but I don't know if the clearances are that close to cause a problem?

[nitroracer]

Have you calculated the mileage manually?

Sitting and idling should use less gas than moving the car.

[88grandmarq]

Hook up a fuel pressure gauge and watch the fuel pressure while driving the car and while the motor is idling.
Inspect the vaccum hose to the MAP sensor, make sure its not collapsing under high vaccum and causeing a restrction.

[85MercPark]

When sitting idleing, gas mileage should go to 0 MPG, cause you are not moving.

[phayzer5]

:lol:

[87mefull]

It did used to read 0mpg or the last mpg it displayed while it was moving (ex:15mpg even), but now it either increases a little in gas mileage at idle or goes down considerabley at idle. In other words, if it last read 14mpg, its either going to continue to drop a decimal point per few seconds until it reaches 8-9mpg or do the opposite.

Today it had a loss of power and ran generally poor, 9 to 10 mpg on average. It ran fine last night and had plenty of power for a lopo. I had to restart it once because the idle was uncontrollable and too high at times, and restarting it made it idle better. The IAC is new and works fine though, even unplugged it to test it. This is without AC or a smog pump and running on hot days seems to cause the majority of the problems.

88grandmarq, where is the map sensor located? Never even considered the map sensor before and my truck had similar problems when the map sensor. It was hard to start just like my car is now and ran lean and generally rough. I should probably invest in a better code scanner also if thats the case. Fuel filter is new and the injectors are all fine, but I'll have to hook up a fuel pressure testor and check the fpr soon to make sure.

This car has got 16mpg in the city recently after I changed the plugs and reset the computer. The problems seem to be reoccuring though after a short time, which is why I thought it might be related to the valve cover gaskets or the ecm itself.

Also, are the valve cover gaskets leaking onto the plugs' eletrodes or just onto the top threads for the spark plug holes in the heads?

[mrltd]

Map sensor is on the firewall, just off center to the passenger side, by the back of the intake manifold.

MIght also be the O2 sensors.

The oil can only mess up the plug wires. It cant leak into the cylinder from the valve covers.

[87mefull]

02 sensors/wiring harnesses are new along with a new egr valve, sensor, solenoid. Scanned for codes, only got 43 and 44, but I might have missed one. I looked at all the grounds, the wiring harness, and the ecm, all checked out ok. I'm going to look again and check the map sensor also.

Couldn't find any vacumm leaks but I would suspect the map sensor. It might be working intermittently, similiar thing happened with my truck.

[mrltd]

Have you replaced the coolant and intake air temp sensors? Those are a common cause of poor milage.

[Blaze86Vic]

Have you calculated the mileage manually?

Sitting and idling should use less gas than moving the car.

Sitting at idle, uses less gas than moving, but the MPG is 0. If you sit, you are not moving, but still using gas. Idling a lot will drapaticaly decreas your mileage.

[87mefull]

Have you replaced the coolant and intake air temp sensors? Those are a common cause of poor milage.

Replaced the CTS but not the IAT sensor. I did do a complete coolant flush though a few months ago and replaced some hoses. Checked for air in the system and it didn't have any in it. Timing is dead on 10btdc with no problems in the spout connection or tfi wiring. Before I replaced the distributor cap, I took off the little vent cap on it and the car ran alot better. It actually helped alot (I've seen similar problems with older chrsyler V8's with humidity trapped in the cap) with some of the running problems and the car idled better. I don't know if all the ford distributor caps don't vent properly even with the little black vent plug or the problem is still elsewhere, and this is with a good MSD cap and rotor (got it with a friend's discount).

Most of the problems are with hot weather driving, it either runs rough or has a hard time starting. It drove like it retarded the timing alot on the way home and it was 90* out. I read in the haynes manual that this is related to the map sensor which has to adjust timing to avoid spark knock at 90*+. It also couldn't idle until I turned the car off. The car was idling way too high and rough with alot of missing throughout the driving range.

[gadget73]

If it starts to run funky as it sits there idling, I wonder if you don't have a leaky injector thats fouling a plug. Are any of your plugs black or wet looking compared to the others?


These cars have no anti-knock sensor, and the MAP has nothing to do with the timing really. Between it and the throttle position sensor, the computer determines the load level on the engine and will adjust timing accordingly. So far as I'm aware, the timing can't retard on these, it can only not advance, meaning it'll go to 10 BTDC minimum and advance up to like 20 degrees from that point.

[87mefull]

Yeah, it might be an injector on #3, it had a little crud vs. the other plugs which were all white. I'll have to check the plugs again though, it misses badly on the other side now though. I was leaning towards those before since it has a bad shudder whenever its warm out, but it was hard to tell. One or more injectors may be working intermittently, the car runs fine sometimes with no misses or shudders, other times it doesn't. I drove the car home today and it ran smooth, gas mileage was a little better too. It was cooler out though, the air/fuel mixture will be better.

I'm going to see if scott can take a quick look at my car this weekend, I've fought with timing, various sensors, piss-poor code scanners, vacumm lines, the egr valve, etc.

Tripminder is definitely messed up also, I don't know what happened to it. I noticed this was a problem when I was getting worse gas mileage with the engine off and the radio on.

I checked all my wiring and it was fine, but the speaker wiring is close to where the tripminder wiring. I think maybe the ground for the tripminder is too close to the ground for the radio, which is throwing it off.

[N A]

Sounds good, keep us posted.

[87mefull]

It was the map sensor, the car ran fine on the long trip up and back to skippyville today. I got 20mpg consistently the entire ride up and 17-18mpg on the ride back. I took a different route back (309 south) because I didn't feel like taking the turnpike back, so mileage was a little worse (lots of stoplights and towns). This was on 89 octane, you allways should run a grade higher when buying gas in philadelphia. My dad's 4.0 99 Jeep Cherokee has to run on 93 sometimes for this reason and its been tuned up.

Car was idling high but the serpentine belt needs to be replaced, it was dragging so the motor raised the idle (watched it do it before I left scott's garage). Power steering pump might be low on fluid, causes the same thing. Main problem was the map sensor, the vacumm tube end was brittle, so I cut it and put the new sensor on.

Merc's running good now , I wasn't disappointed with the stock lopo's performance on the drive either, probably since it has Hess 89 octane in it.