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2002 Mercury Mountaineer Enginer Missing

Tiny
BLUKE
  • MEMBER
  • 2002 MERCURY MOUNTAINEER
  • V8
  • AWD
  • AUTOMATIC
  • 107,000 MILES
The engine has a habit of running rough during warm up. It does not do it with every cold start up but is getting close. It does not miss consistently. It will run smooth for several seconds and then miss once. It will run fine for 5 seconds miss once or twice. It can miss randomly for 5mins but never in a consistant pattern. It misses at all rpms (except idle) and at load and no load on the engine. The problem tends to go away once the engine is at operating temperature but not always.

Here is a list of things I have tried.
Cleaned the MAF sensor.
Checked air filter
No codes on the OBDII tester
O2 sensors good
Checked all the resistance on the coil packs
Checked all the resistance on the fuel injectors
Cleaned the ERG valve
checked for vacuum leaks
Checked the fuel pressure regulator
Checked the fuel filter
Checked the fuel pump
Checked the fuel pressure in the fuel rails
Checked the idle by pass valve
checked the PVC valve
Checked the thermostat
The tps is 20K miles old.
The fuel filter is 25K miles old.
The fuel injectors were professionally cleaned 25K ago.
No check engine light.

I have spent many hours troubleshooting this and the problem has been going on for about 30 days off and on-slowly getting worse.

I have learned that I have a limited amount of time to diagnose the problem before it goes away for some reason. It typicaly "fixes" itself after an engine stop/start cycle. Once the problem goes away, I have to wait until a cold start to create the problem again. Once the problem goes away the engine runs perfect as long as it stays running and never goes back to missing until it cools down.

Any advice would be helpful before I take it into a dealer and spend hundreds of $ trying to fix it.


Best regards,
Brandon
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Saturday, June 13th, 2009 AT 11:26 PM

21 Replies

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
When you say you inspected the MAF, IAC, TPS and throttlbody, do you have a scantool that reads live data? MAF on Fords dont "clean" well, IAC's are almost impossible to figure even with an NGS II, ECT MAF IAT and dirty throttlebody and fuel pump pressure? All possibilites.
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Sunday, June 14th, 2009 AT 12:24 PM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
Did you get my reply to your post on Sunday, June 14?

Thanks,

Brandon
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Thursday, June 18th, 2009 AT 10:00 PM
Tiny
MERLIN2021
  • MECHANIC
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No I only see this one at the top, also in case I forgot to mention it, check the ECT (engine coolant temp) sensor, it acts as the "choke" on SEFI engines.
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Friday, June 19th, 2009 AT 12:44 PM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
I wrote a lengthy relpy last Sunday to your 1st post and apparently it did not send. I'll try to retype it this weekend for you read.

Sorry for the confusion,

Brandon
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Friday, June 19th, 2009 AT 1:35 PM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Was it an email or post? If you emailed it, look in your out box and just resend it.
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Saturday, June 20th, 2009 AT 4:15 AM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
I apologize for the delay in getting back with you. Life has been coming at me fast. I'll do my best to answer your questions from your 1st response.

I do not have a scan tool that reads live data. Here are the tests I performed.

I have a data acquisition unit that I used to read live fuel pressure from the shader valve on the fuel rail. I recorded the pressure every 1msec. The pressure never increased or decreased while rapping the throttle, idle, or while the missing was occurring. There was one phenomenon that I noticed and could not explain. The fuel pressure increased every 2.3sec by 5psi. The increase only lasted 20-30msec and then went back down to normal (68-72psi). This cycle was not affected by the engine rpm or missing. This cycle occurred in every graph that I recorded. The resolution of the graph is so fine, that I believe you can see the fuel pressure drop by a couple psi as each injector opens and closes. Or, the oscillation that I see on the graphs is the fuel pump pulsing a small amount of fuel for reach rotation of the pump. I can send the graphs if you wish.

I cleaned the MAF with a can of MAF cleaner purchased from Autozone. (I use a K&N filter).

I visually inspected the throttle body. It was clean with no residue.

I checked the ECT by resistance and voltage. I found a table that told me the coolant temp based off the resistance (if ECM is disconnected) and voltage (if ECM is connected). They both checked out ok.

I have not checked the IAT. I don't know where it is.

I ohmed out all the injectors and coil packs. I did not find a resistance that was significantly higher or lower that would indicate a problem.

I disconnected the hose from the IAC to the throttle body duct. The engine running at idle sputtered and quit. I also disconnected the electrical connector to the IAC. The engine again died. After your 1st replay, I decided to remove the IAC and test it. The resistance read 9.6ohms and I fired it using direct 12VDC from the battery. The IAC clicked back and forth about 1/8" (at most). It is not a motor like other vehicles, but a solenoid that opens and closes a port. I cleaned it with carburetor cleaner and reinstalled it. The engine did hesitate at first but since the time I cleaned it, the engine does not seem to hesitate like it did when I first posted the problem. I don't know if it is because it's not noticeable driving or if the IAC was the problem and just cleaning it fixed it. If the IAC was the problem, do you recommend replacing it so the problem won't come back?

I welcome your wisdom.

Brandon
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Tuesday, June 23rd, 2009 AT 9:59 PM
Tiny
MERLIN2021
  • MECHANIC
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Is your K&N wet or dey? If it's an oil soaked one, replace the MAF, cleaning does not usually work! I have replaced a few for performance and stalling issues when used with these filters, and it always solves the problem. GM has a tesh bulliten out for this as well.
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Wednesday, June 24th, 2009 AT 2:36 AM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
My K&N is oil soaked. I have to spray it with oil after cleaning it (if that is what you mean).

This morning on the way to work (3 mile drive) the engine started missing again. Not as bad, but the problem is still there.

I also had a fast idle when I pulled into the office parking lot, which I get about once a month. The only way I can get the engine to idle down is to turn the engine off and then immediately restart it.
Do you think the fast idle is caused by the MAF?

Is there any way to check the signal from the MAF to the ECM to determine if it is at fault?

Thanks,
Brandon
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Wednesday, June 24th, 2009 AT 7:55 AM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
2001-2003 Ranger, Explorer Sport/Sport TRAC - no start/buck jerk some 2001-2003 Ranger and Explorer Sport/Sport TRAC may exhibit a no start, no communication with PCM using WDS/NGS or a miss/buck/jerk while driving. Check for ground G104 integrity. G104 is the PCM and PCM Relay ground. Remove the G100 attaching nut from the ground stud in front of the battery at the radiator support. Torque the G104 stud to 10-14 n-m (8-10 LB FT). Reinstall the G100 ground wire and attaching nut. Torque the G100 attaching nut to 8-10 n-m (7-8 LB FT).
Also inspect the PCV hose where it attaches to the manifil, they tend to loosen up, or flake apart, especially on high mileage cars.
MAF testing requires a scan tool that can read PIDs and a volt ohm meter, instructions are emailed in PDF file.
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Wednesday, June 24th, 2009 AT 1:18 PM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
I have checked the ground connection and PVC and hose to it. I also checked other PCM ground connections. Everything looks good.

I have been working through the email you sent me regarding the MAF sensor. Nothing has turned up yet.

I have a fast idle now almost daily and with it the engine stumbles while driving. They always occur together.

Out of frustration I unplugged the MAF while under fast idle. The engine really didn't change. I plugged it back in and unplugged the TPS. The engine idled down nicely. When I reconnected it, the engine went back to a fast idle. I did this several times. The fast idle always came back the TPS was reconnected.

Does this indicate a TPS problem?

Thanks,
Brandon
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Saturday, June 27th, 2009 AT 1:09 PM
Tiny
MERLIN2021
  • MECHANIC
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It could be, but the MAF and tps are tied to injector pulse width, if the maf was dirty, I suspect that, or the PCV rubber elbow has a crack or rotted out a bit.
Test TPS like this:
9) Check Voltage Between VREF & SIG RTN Circuits At TP Sensor Using a DVOM, measure voltage between VREF and SIG RTN circuits at TP sensor harness connector. See Fig. 38-Fig. 42 . If voltage is 4-6 volts, replace TP sensor. If voltage is not 4-6 volts, reconnect components and go to TEST C, step 1). 10) Check TP Circuit For Short To VREF Or VPWR Circuits Turn ignition switch to OFF position. Leave TP sensor disconnected. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals and repair as necessary. Using a DVOM, measure resistance between TP circuit, VPWR and VREF circuits at PCM harness connector (both VREF circuits on 150-pin PCM). Both VREF circuits on 150- pin PCM models. If any resistance measurement is 10 k/ohms or less, repair short between circuits. If all resistance measurements are more than 10 k/ohms, replace PCM.


https://www.2carpros.com/forum/automotive_pictures/62217_TPS_4.jpg


Pcm connectors are shown below.


https://www.2carpros.com/forum/automotive_pictures/62217_pcma_1.jpg



https://www.2carpros.com/forum/automotive_pictures/62217_pcmb_1.jpg



https://www.2carpros.com/forum/automotive_pictures/62217_pcmc_1.jpg

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Saturday, June 27th, 2009 AT 5:25 PM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
The voltage between the Vref & Sig Rtn is 4.9V & between Vref & TP is 4.7V. The voltage was measured with the TPS unplugged and engine running at slow idle. Am I suppose to measure the voltage with the sensor connected to the PCM and engine running?
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Sunday, June 28th, 2009 AT 4:12 PM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Yes but be careful not to ground the wires, use a pin to penetrate the wires. Alternate method is to unplug the TPS with engine off, measure resistance, as you move the throttle, the needle should sweep smoothly, no sudden jerks, have you replaced the MAF?
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Sunday, June 28th, 2009 AT 5:06 PM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
The TPS resistance was jerky between Vref and Signal Rtn & the sensor read 4.9V while the engine was running.

I plan to replace the TPS tomorrow (if in stock) & go from there.

I have not replaced the MAF. It is an order part. Do you recommend the refurbished or brand new? If the TPS does not solve my problem, I'll replace it also.

I'll keep you posted.

Brandon
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Sunday, June 28th, 2009 AT 10:42 PM
Tiny
MERLIN2021
  • MECHANIC
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Brandon go to Rock auto. Com and look for the ford unit, I dont use refurb when it comes to MAF. Let me know. If TPS was jerking the needle, it should go!
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Monday, June 29th, 2009 AT 4:06 PM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
I replaced the TPS last night and the engine runs much better. The fast idle is gone and the engine ran well the couple miles I test drove it last night.

Since this problem comes and goes, I'll drive it a couple more days and get back with you after July 4th on a final verdict.

Thank you for the help thus far,

Brandon
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Tuesday, June 30th, 2009 AT 7:47 AM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
I'll be checkin in on it!
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Tuesday, June 30th, 2009 AT 1:59 PM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
Replacing the TPS seems to have fixed the problem. The engine has run well for several days in a row. I'll drive it another week or so, and give you a final verdict. But I'm hopeful my problems are behind me.

Thanks again for your insight,

Brandon
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Wednesday, July 8th, 2009 AT 9:51 PM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Good work B.
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Thursday, July 9th, 2009 AT 6:56 AM
Tiny
BLUKE
  • MEMBER
  • 11 POSTS
Merlin,
The mountaineer is still running well. I consider the problem resolved.

Thanks for the help!

Brandon
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Wednesday, July 22nd, 2009 AT 7:57 AM

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