99 X flat spot/hesitation

[V8-X]

99 X - 5.0 - AWD - Auto Trans

All started with bad #4 spark plug.

In June 2002, my engine started to mifire & the CEL came on. This was determined to be the #4 spark plug. Which I replaced and from there the CEL turned off and has not come back on. Since then I've had a loss of power/flat spot and rough idle (first 5-10 mins of driving warm or cold start).

I've taken the truck to Ford twice and to two independent shops. Ford couldn't find the problem, stating everything shows within operating spec ranges. One independent shop couldn't find anything, while the other stated the rough idle was the IAC & the loss of power/flat spot was the FPR. I have paid $391 + tax in diagnosis fees alone to find no cure.

Since having the truck checked 4 times, I have replaced the following which has not corrected either of the problems. All replacement parts are Motorcraft or Ford parts:

IAC, FPR, EGR, PCV, Fuel Filter, all 4 O2 sensors and all 8 plugs & wires. I have cleaned the MAF/MAS and I have purhcased a new TPS, which will go in this weekend.

The symptoms are most noticable under the following conditions: accelerating with RPM's under 2000, accelerating while on an incline, accelerating from coasting or during light acceleration. The engine & exhaust tone are slightly deeper/louder than before the problem started. At times the Trans sounds like a Manual trans when it is in to high of a gear, but this is an Auto trans. I do not believe it to be a bad Cat., as the backpressure tests come out ok. When over 2000 RPM's, the majority of power is there, but I still have 4 banger Geo's passing me and I have the 5.0V8.

Any thoughts, advice, suggestions and/or help would be greatly appreciated. I've been trying to cure this for the last 5 months, and nothing has worked. Ford seems as clueless as I am.

Thanks in advance for everyone's input on the possible solutions

 

[fordkrazy]

sounds to me like it would be a tranny prob. have the pan dropped and then flushed after refilling. does it seem to shift to a higher gear too soon?

 

[section525]

Maybe replace your coil packs? They've been known to cause some funky problems on V8 Xs.

 

[fordkrazy]

good point section525....those are big bucks but it may be the problem...i didnt think of that but maybe the reason your #4 plug went bad was cause the pak w/ the #4 on it was going out. dont know how the plug would trip a CEL

 

[V8-X]

Thanks for the suggestions, and it sounds like some good advice.

Fordkrazy - Thinking this might be the problem, I went ahead and had the trans. serviced in August, so I do not believe this is the culprit. As far as I can tell, it still switches gears at the correct shift points. Only when it does switch gears, this drops the RPM's below 2000 and brings me to situation of having a lack of power.

section525 & Fordkrazy - The ignition pack sounds like something I may need to check. By chance, is there a way of testing these prior to replacement?

Just curious, but wouldn't the CEL light up if there was a problem with the ignition pack? Since the CEL came on to warn of a bad plug, wouldn't the CEL stay on if it wasn't the plug that had the problem? Just a thought.

Thanks again for the help, I'll check this out this weekendwhen I install the new TPS. Of course any other advice on possible solutions would be helpful.

 

[fordkrazy]

i dont think the coil pack would send a trouble code as there is no feedback given to the computer from them....so the computer has no idea what they are doing....it just tells them to spark.

just a few more questions....how many miles and what did you clean the MAS with?

i cant help to think that unless something is wrong with the tranny that it sounds like a closed loop/open loop problem w/ the emissions....did you replace the EGR valve or the sensor?...i doubt the valve is bad as they have improved these greatly from the old days...its usually the sensor....but the thing is that usually the things that cause this sort of problem will trip a trouble code and light the CEL....

im stumped

 

[Robert]

Somehow the PCM can detect when individual cylinders are misfireing. I don't know how it does it but if either the plug, wire or coil is not allowing a cylinder to fire, you will get a mis-fire detected on that cylinder.

 

[fordkrazy]

maybe through a knock sensor?

 

[Robert]

Except that the knock sensor is basically a piezo microphone that is attached to the top of the valve covers. It has no way of detecting which cylinder isn't firing.

I just read the procedure to detect a mis-fire though. It is:

1) Start the engine and drive the vehicle to a location where speeds can reach 88 to 105 km/h (55 to 65 mph) and coast down to 56 km/h (35 mph) without traffic interference.

2) Perform following drive procedure three consecutive times.
Accelerate on highway to 97 km/h (60 mph) . Maintain speed for 30 seconds .
Coast down with foot off the accelerator pedal from 97 km/h (60 mph) .

This is basically the same condition my engine was under when mine threw a random mis-fire code on all but one cylinder. I had just gotten over a long grade and let off the gas to coast down. My CEL lit up. When I scanned it I had mis-fires on all cylinders but #4.

All of the things it lists that can cause a mis-fire detect code:

1) ignition system
2) fuel injectors
3) fuel pressure
4) evaporative emissions system
5) EVAP canister purge valve
6) base engine
7) running out of fuel

One of the things that you look at during troubleshooting steps is the DPFE sensor. That makes sense now. Since the computer knows which cylinder should be fireing, if the differential pressure wasn't as expected on the DPFE, it should be an indication that the cylinder didn't fire.

 

[fordkrazy]

where did you get this information? it sounds very valuable.
ok now some questions...
is this the only way to get the PCM to throw a code for a misfire? or will it do it under other driving conditions....if it is the only way then i would advise to do that to see if it throws a code....its hard to determine the cause of lack of power unless you have a code...otherwise it may be mechanical or the PCM's self test is bad and its running in fail safe....but if its in fail safe you will definately know it....basically if you cant get it to throw a code for anything start checkin for things that arnt computer related....you have replaced almost everything that would cause this problem and its not fixed....that tells me that may be something mechanical

...oh yea...and what is the DFPE?

 

[Robert]

I got the info. from my subscription to www.alldata.com. It is also in my Ford service CD.

One of the readiness checks that is ran when you first start up an OBD-II equipped vehicle is a mis-fire detection. I didn't look long enough to find out if there are other scenarios that could set a mis-fire code so I'm not sure on that one.

The DPFE is the differential pressure feedback ??? sensor. It has two vacuum lines that run to it. It's purpose is to sense a difference in pressure between the two lines. The information is fed to the PCM. It is mounted to the side of the valve cover, right behind the oil dip-stick tube on my '97 SOHC.

 

[V8-X]

Thanks again, and in response to your questions:

Fordkrazy: The truck has just under 58K miles, and the MAS was cleaned with an O2 safe Carb. cleaner. Also, I have replaced the EGR valve, but not the DPFE or the sensor.

Couple more questions. I have heard that the Explorer's have had problems with the DPFE, is there a way of testing this to insure it is actually working? Does the DPFE need a gasket when replacing? Also I've heard that the DPFE tubes get clogged as well, so should this be another area to check? I will most likely replace the DPFE and the tubes just in case, but I wanted some advice prior to actually swapping parts.

Since replacing the plugs, I haven't been unable to get the CEL to turn on again. Ford hasn't been much help, as I just spoke with a dealer again yesterday. Here's their diagnosis:

Checked Codes & Monitor PID's. Perform Pinpoint Test & Power Balance Test. Checked Freeze Frame Data on Cat. Efficency. Results-Normal-Could not verify concern at this time.

I will be trying to replace the TPS this weekend, and I will most likely oder a DPFE & DPFE tubes. Any suggestions on where to go next? DPFE, EGR/EVR Sensor???????

Thanks everyone!!!

 

[fordkrazy]

hey guys....i looked into this DPFE sensor more and found that it is accually what tells the computer how open or closed the EGR valve is by detecting the pressure on both sides of the line.....ive cleaned this before on my 4.0 but never knew what it was exactly (just goofin around)....i just replaced the hoses on it to be sure....they were pretty crusted up.....this is probably what is wrong with it as the egr valve is always closed a WOT (wide open throttle)....so the lines are probably crusted up and the sensor isnt getting the correct reading but it is getting a reading within range which is why its not throwing a code

oh yea and reclean your MAS with cloride free brake cleaner....the carb cleaner has a light oil in it to lubricate linkages and chokes....this is bad news for the MAS...i wish everyone would spread the word that carb cleaner is NOT what to use...it often makes it worse than before cause unless you live in a very humid climate or dont replace your air filter often....you shouldnt need to clean it

 

[V8-X]

Well everyone, here are some more notes to take into consideration.

Just replaced the TPS yesterday. So far it seems as though the Throttle Response is a lot better. The truck seems to pick up speed and keep its speed better now, than prior to the replacement of the TPS. Only problem is I still have a very slight hesitation/flatspot in two areas: When accelerating from a dead stop, or accelerating from a cruising speed. The flatspot/hesitation is less noticable since replacing the TPS, but is still there. (below 2000 RPM's).

Question: Prior to any problems, I was getting 15 mpg city. After this problem started, the mpg dropped to 13-13.5mpg. Now after replacing the TPS, the mpg has dipped again. Now I'm getting about 12mpg. I read in my Haynes manual that the TPS is not adjustable. Could I have installed this incorrectly or is some adjustment needed? I'm curious why the mpg dropped after the new TPS was installed.

Each part I have replaced has given the truck a little more life/power, but is not where it used to be. Here is another list of parts I have replaced. EGR, TPS, IAC, PCV, plugs, wires, fuel filter, fuel pressure damper & O2's (4).

I have a new DPFE, so I'm gonna try to get to it & the DPFE tubes this weekend. Hopefully this corrects my problem completely. Any further suggestions or advice would be greatly appreciated, since neither Ford nor 2 independent shops can seem to find a problem without the CEL on.

 

[fordkrazy]

ill bet you anything its the PFE all the way.....what your describing now sounds like a egr problem and since you replaced the valve the only thing left is the PFE

man your car has sure given you the runaround....lol..i know how that feels

 

[TPLYNCH]

Did you reset the computer after replacing the TPS?

 

[V8-X]

I did reset the computer after the installation of the TPS. I disconnected the Negative terminal on the battery for about 3 hours, I believe this should be enough time to reset the computer. I hear you only need to diconnect the battery for about 10-30 minutes, but I just wanted to make sure.

Hopefully you're correct with the assumption that the problem is the DPFE. I've spent a lot of money and time on this truck the past 3-4months, so it would be nice to have it running healthy again.

Again, I will post the results of the DPFE swap and cleaning of the DPFE tubes. Let me know if there are any other suggestions, but I do want to thank everyone so far. The help is greatly appreciated, and does not go unnoticed.

 

[V8-X]

Well, it looks like I've finally gotten my problem fixed. I broke down and took the truck to Ford again for another diagnosis. This time I went to a different dealer though. The Tech informed me that he could not find any problems with the truck, except that it needed the newest calibration for the PCM. What do you know, after the recalibration the V8 power is back. I believe this was TSB 99-8-7, which refers to most 97-99 X's. So anyone experiencing this sort of problem, you may want to check with your dealer about getting a recalibration for the PCM. Thanks again for all the help and suggestions everyone, it's been benefitial.

 

[james t]

just a little info- you said the first time you had it serviced, the dealer said the flat spot could be the FPR. im pretty sure your 99 is "returnless" fuel style, and doesnt even have a FPR. the fuel pressure is controled at the pump. just a FYI.

 

[V8-X]

Actually it does have a FPR, but Ford now calls it something like a "Fuel Pressure Damper" instead of a Fuel Pressure Regulator. This is at least what I was informed by the local dealership. I do not know if the Damper performs a different function than the Regulator or not, but my Haynes Manual & the dealer informed me that I do have one. This is also the 5.0 V8, which may have a different setup than either if the 4.0's. thanks for the FYI though.