Engine missing badly, need help asap!!

[seether038]

hello everyone, I am new here but hoping someone can give some sound advice on my Explorer. its a 99 sport 2wd, bought it used a couple of weeks ago. It had only a slight little "miss" or stumble when we test drove it, and it did show 2 codes 171 and 174, lean on both banks. When it idles sometimes it runs perfectly, other time it starts a very rough idle almost wanting to cut off completely. I have installed new plugs, new fuel filter, changed oil, pulled and cleaned the maf sensor. It is now missing very badly if I try to accelerate very hard at all. once its at about 55-60 mph starts missing very badly with check engine light flashing..

Today I bought a fuel pressure gauge and checked my pressure with very interesting results. with only the switch on and not running it only read at maybe 12-14 psi, I double checked with just the switch on and it was the same. the Haynes manual calls for it to be 62-65 psi and I am only showing 12-14???? I dont understand what that means?

When I start the truck it shows an acceptable range of 66-68 psi pretty steady, but does drop 1-2 psi when I gave it some pretty good throttle. Really doesnt seem to miss at idle like that, pretty much only when I try and give it some gas while its in gear? Does it sound like I need to go ahead and do the fuel pump?? Or any other suggestions?? Thanks for any help I am ready to get this thing running right, it only has 105 k on it!!

 

[2000StreetRod]

Which engine?

If you have the SOHC V6 your upper or lower (or both) intake manifold gaskets are probably leaking. They are fairly cheap but take a while to get to. See Lean condition procedure

By the way, welcome to the forum and congratulations on purchasing one of the best looking mid size 2 door SUVs ever manufactured!

 

[seether038]

yes its the sohc v6 thanks for the reply!!! had not thought of that yet. What would you make of my fuel pressure reading only 12-14 psi with the key on? its supposed to be 62-65? thanks for the help ill look into that. WAs thinking of replacing the coil packs too

 

[2000StreetRod]

possibly weak pump or leaking check valve

The fuel pump only runs for a couple seconds when the ignition is switched on. I suggest monitoring the fuel pressure and cycling the ignition switch each time noting the pressure increase. The pressure should increase to 60 psi in three cycles. Then watch the pressure decrease with the ignition off. If it plummets to near zero psi in a couple of minutes then you either have a fuel leak or a bad check valve.

 

[jonlax]

Fuel pressure can be misleading. Pressure doesn't equate to volume and volume doesn't equate to pressure.

I'd start with a smoke test of the intake but if you dont have one a can of carb cleaner will do the same thing. Start your engine and while idling spray the carb cleaner around the intake slowly. Little bursts in different points on the intake working your way around. Listen for any stumbles, fisheries or missfires. If you hear any RPM differences while spraying in a paticular area visually inspect where exactly the leak is coming from to determine the problem.

Usually when you have lean codes its always the intake gaskets leaking. Now dont get me wrong a fuel problem can cause the same problems along with a dirty or broken MAF but a proper diagnosis will save time and labor of throwing lawn darts with parts.

Good luck!

 

[seether038]

thanks for all the help!!I just left came back in drove for about 45 mins only easing onto the accelerator and she was running like a top!! If and when I "get on it" thats when the fun stuff starts...also the other day it cut off as I pulled into my yard acting like it was out of gas but the gauge showed almost 1/4 of a tank. Read on some forums that some explorers dont like to sit at an angle and to check the inertia fuel pump switch, I did and it was fine. I poured in 1/2 gallon fresh gas and it started very slowly. So I was kinda thinking that it may have sucked some trash up somehow? Maybe I need to look into cleaning/replacing the injectors too? I dunno I was just thinking that it running out of gas the other day may have something to do with it?

Thanks for all the help I have been totally lost its nice to find a place where other ford owners are helping one another!!

 

[seether038]

also whats the best method to find a vacuum leak, tonight while under the hood I can definitely hear a hissing noise coming from up towards the firewall on the passenger side. Is this a normal sound for this 4.0 sohc engine? I dont have access to a smoke machine and Im kinda scared to use carb cleaner on it but I have seen videos of people using cigars and such.

BUt there is definitely a hissing coming from that area, so thats where Im gonna start looking...thanks for any and all replies!!

 

[2000StreetRod]

read the procedure

The engine misfire procedure I provided a link for includes a link to a thread explaining how to build a smoke machine. This is the safest and most accurate way to detect a vacuum leak. Using carb cleaner or some other combustible aerosol is not very effective on leaking intake manifold gaskets located deep under the upper intake manifold. Also, the IAC valve and PCM attempts to maintain the commanded idle speed negating much of the effect of the aerosol. The engine misfire procedure also includes a link to a thread showing all of the upper intake manifold vacuum ports.

 

[seether038]

thanks so much, gonna go over all this this weekend. I am convinced its either starving for fuel, or has one really bad vacuum leak somewhere....I will post back when I find the culprit. Thanks again everyone!!

 

[seether038]

I was starting to think burnt valve(s) so I did the old newspaper in front of tailpipe trick but it only seemed to blow out, not suck in so I think it passed this test?

 

[seether038]

think I got it fixed now was plug wire boot grounding out on the block, got a new wire installed and checked the others and its runnin great now!! thanks for all the help