Rough idle bad mpg
 

I have a 1992 Ford F2 50 with 460 I'm getting intermittent rough idle and bad gas mileage the truck has plenty of power and runs decent at high rpm but it has a slight miss at low RPM I would think that it's the ignition timing being a little off for a vacuum leak I took some starter fluid and sprayed all around the hood to and all over the hoses but notice no change in RPM the truck has a new distributor cap and rotor as well as new spark plugs and wires and an O2 sensor I did a vacuum test and it's holding very steady at 18 inches high did a compression test and all cylinders are between 150 and 155 I'm not sure what else I can do besides start replacing things which I don't like to do but this truck is all computer-controlled and I can't even change the ignition timing or even tested does anyone have any ideas on what I can look for to take care of this it just has a very slight miss at Idle and it gets bad gas mileage on the freeway which might be it in part due to the bad will alignment which I'm going to get fixed budwin uns standing by the exhaust it's like I hear little backfires in there maybe like the ignition timing is off but this is EFi

Well the EFI is your friend, not your enemy here.

First, yes you can check and change the ignition timing, the EFI has nothing to do with that, at least in regards to the base timing.

Seecondly. the EFI has self diagonstics built in, so you need to check for codes. again, the EFI is your friend here, not your enemy as checking for codes is easy. You will have to buy a tool to do it yourself, (or you can count flashes, the tool is the way to go here)just like you have to buy a timing light (again, just a tool to get the job done) to time the engine. Nothing out of the ordinary there. It is just a tool.

Third, it sounds like you are taking stabs in the dark on this, probably should get a service manual and follow the diagnostic steps.

Remember, EFI is not some mysterious system, it is a proven system that may require different steps to troubleshoot than a older system, but the mean time between failures as well as engine life is greatly increased with it, you just have to change your approach to it and check for codes first! Just like you have followed certain steps in checking the mechanical systems in your truck, there are steps to be followed as well in diagnosing the EFI. Code checking if first! (I will keep saying that!)

Please post more as you get the codes, lots of helpful people on here.

You did not post what your milage is, but I get a honest 8 mpg with my 460 in my 1990 generaly, but I see up to / just under 11 on the hiway, but then I use my truck as a truck and it has a dump insert in it which adds a bit of drag. I also move right along and have no problem putting the go pedal to the floor as needed. (especialy on hills with a full dump insert and dump trailer)

David

My Check Engine Light is not on.

I went to this website:
Fuel Injection Technical Library » How To Run a Self-Test

I tried doing this. I put a test light in the "STI" plug and grounded it on the hood hinge (the hood hinge seems to work well with all the other testing I have doen). I turned my key to the "ON" position. I heard the fuel pump. About 30 seconds later I heard the fuel pump again, at which point the check engine light finally went off, but never came back on again.

for timing, I am supposed to disconnect the single wire that is with the others leading to the distributor (SPOUT connector), and set it for 10 degrees BTDC? My manual doesn't have these instructions but that's what I find online.

I checked the base timing and it is about right on, and I can't seem to move the distributor when I totally loosen the hold down clamp anyways, which is really wierd.

I did not replace the plugs or wires or caps, the person who owned it before me did. But I did go back and check them all and saw that they were new, when I did the compression check. They looked very white as if the truck is running lean (they almost looked like they were too hot of a plug, they were Autolite 25's).

I did replace the PCV grommet because it was totally loose and the PCV valve wouldn't even stay in there. Oddly enough that seemed to help but there's still some rough idle there. I can feel it in the seat and see the passenger seat shake some. Whereas the passenger seat used to always shake at idle, now it just has spurts of shaking at idle. So now I'm thinking this may be more vacuum leaks. It could be any of them in this spaghetti of air hoses. And it could be a collection of small leaks that are too small to pick up individually with the old starter fluid test.

I wonder how much it would cost to replace all of the hoses.

I checke and with empty driving on the highway with a little of in town of stop and go, I got about 10 MPG. It has E4OD with 4.10 ring and pinion. I think the 4.10 rear gears are what's killing me on the highway.

One thing to remember is that you can have codes, without a CEL on. The light flashing test is really a poor substitute for the proper diagnostic tool.

The dist is probably frozen, you may have to use a light touch with a hammer to get it to spin. The fact that it has frozen is another advantage of the electronic age - longer mean time between failure as your truck has probably never had to have the timing adjusted as there is nothing to get out of adjustment! (timing chain wear not withstanding, although that is not a adjustment like degrees of dwell or a different rubbing block/point set design of the older systems which has a direct effect on timing)

The mileage does not seem bad to me, that is about what these trucks get, more or less. They just were not designed for economy, but to move a load, day in and day out.

I only get about 3 mpg with my C600 dump truck, and it only has a little 330 cid gas engine so it could be worse, although the dump is cheaper to run when loaded as I can move so much more weight than the F250 at 8 mpg. Neither though would be the right tool for a commuter vehicle!

David

Doesn't matter.


Forget the test light and just do as the procedure suggests and put a jumper(paper clip) between the STI and Sig-Rtn pins, turn the key to run and count the flashes on the check engine light.

iac sensor