I went to town today to look for a leak down tester but couldnt find one. Does a compresion tester work as a leak down tester also or is it a different tool?

I did get a digital multi meter and am going to try my hand at testing sensors and stuff. I found out how to check relays and tps's and found out you can test fuel injectors also. Talked to a very good mechanic I know and he ran a obd test on it and thinks the 542 code is the problem. He thinks it's a bad ground in the computer, relay box or a connector going to the fuel tank. He said he could fix it but it could get very expensive because it could take hours to track down and fix the bad ground or replace parts. I want to fix this my self but am getting frustrated. I don't have a grand to throw down on it. If it's a bad part I think I could fix it but if I have to track down a bad wire, well that has me worried. I've looked at all the accessable connections and cleaned them going to play with the multi meter tomorrow thest the fuel injectors and tps. Dont know how to track down a bad ground though.

 

Think I may have found it!!!! I think it's the map sensor. I read if you pull the plug on it and it runs better it's the map. Well I did that and it quit sputtering. I just need to know it this is the map. It's close to the fire wall and had a three prong plug and one vacume on it. Also it's on the passenger side. Kind of a flat box. Also it has a crack in it that is visible.

 

You just use a regular fuel pressure gauge at the fuel rail for the bleed down test, watching for pressure drop after the engine it shut off. Here's a link for the MAP w/ pic! http://www.fordfuelinjection.com/?p=27 I thought I mentioned the MAP already, guess not!

 

Well it wasn't the map. Just droped 50 bucks on it. Don't understand why it would run smooth with it unplugged. Guess I'll try the leakdown test next. It starts and runs so good untill I step on it hard. I can drive all around and not have it hesitate but accelerated hard and miss miss miss. The leak down test will determine what? Thanks again.

 

Anytime a sensor is replaced you should disconnect the battery for 5 minutes to clear the Kept Adaptive Memory (KAM) after which it rebuilds using all sensor input. Give it a try! The bleed down test tells you if you have injectors not closing or hanging open. You should be running Seafoam or Lucas Injector cleaner in your gas anyway as that will usually cure hanging injectors & improve fuel atomization. Seafoam especially, if you think your gas might have moisture in it. I don't remember if you said you did the Seafoam combustion chamber treatment recently? If not, this would be a good time. C/C deposits cause fuel wicking.

 

I did recently use Lucas in the gas tank and poured B12 in it after it started messing up. I will do the leak down test asap. At least it still starts and drives ok, just cant accelerate to much. Will the leak down test have anything to do with this code I'm getting.

 

Too bad you don't have another Fuel pump relay laying around, to see if that code would go away. Next time your at the boneyard, grab one! Something's causing that code. Grab the PCM relay next to it too! F/p relay is usually green base, PCM, brown. They'll come in handy sooner or later (if not now). Check f/P wiring too.

 

All my relays are black with the same part number. Not sure which one is the fuelpump relay. There are some red and green fuses beside them but I have know idea what they go to. Most fuse boxes I have seen have name info printed on them that tell what each fuse is for but this box doesn't. I tried switching the relays around to no avail. Is it possible to test the relay with my multi meter? Can someone post a pic/diagram to show me what my fuses and relays are going to? I searched but can't find any info. 94 F140 4.0 auto. Also is there some kind of relay on the fram rail under the bed I need to check? I've looked at all visibal connections and cleaned them that were acessable. I'm going to do a leak down test asap also.

 

The fuel pump relay has a yellow wire, a red wire, a blue/orange wire and a green/yellow wire. The yellow wire will always have power. The red wire will have power with the key on. The blue/orange wire is the ground trigger wire. The green/yellow wire goes to the pump(s) and will have power for a few seconds when the key is first turned on but truck not running and will always have power with the truck running. No other relay on the frame.

 

Thanks!