Random miss - can't figure it out - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 52 (permalink) Old 03-01-2009, 04:59 AM Thread Starter
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Random miss - can't figure it out

Early '99 Crew Cab 7.3PS 4X2 192K miles. All stock...

Originally started out what seemed to be a cold start issue....In the morning, it normally be a bit sluggish. 1 in 10 it would romp. Only died once in about 4 months since I had it. Sometimes it would be fine. As I got about 5 miles down the road...it would warm up and run fine.

Gene ran the codes for me along with a contribution and buzz test. No codes, buzz test was fine. Contribution showed low on 8 the first time....then low on 5 and 8 the second. Recommendation was a look at the IPR.

I pulled the IPR, looked fine....cleaned it anyway. Put it back, no change.

About a month ago, cold start, jumped on the highway for about 3 miles, went up an on-ramp and as the lockup disengaged the RPMs dropped right to zero. Waited 15 seconds, truck started up and no more problems.
Two days later I was driving up the highway and I head a distinct change in tone....it sounded like knock.

When I stopped, truck was missing badly...felt like a gasser with a HUGE Cam and a nasty lope. When I gave it throttle, it couldn't feel it.

I've replaced the oil, fuel filter (bowl was pretty nasty), GP relay, CPS (which resulted in a failure of the Tension assembly and Serpentine belt....now both new). GP's have all been ohmed and look good.....I haven't had it romp in quite some time....but it will idle crappy in warm or cold weather when I start it.

I've tried using an IR gun to see if one of the holes wasn't firing....but each runner seemed to be about the same temp (around 270deg).

Worst of all....problem is completely intermittent. I fired up the truck this afternoon after not running it for a couple weeks and it felt pretty smooth. No miss. No knock. WTF?

By the way....Why do Autozone and Kragen both tell me my serpentine should be a 1215 (121.5") instead of the 1223 (122.7") that actually fits? A little online research seems to indicate the 1215s were indeed for the 99 and 00 trucks....why does mine need a 1223?
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post #2 of 52 (permalink) Old 03-01-2009, 05:01 AM Thread Starter
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Re: Random miss - can't figure it out

By the way...don't know if its relevant....but ANYTIME the lockup disengages from highway speeds, the RPMs drop too low and the truck flutters between 500 and 750 RPM until it dampens out.
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post #3 of 52 (permalink) Old 03-01-2009, 05:05 AM
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Re: Random miss - can't figure it out

You say you replaced the fuel filter. Try this. Drain the fuel bowl, remove the fuel filter cap. Fill the bowl with Seafoam. Replace cap. Put the couple ounces left of the Seafoam in the fuel tank. Start the motor and let it run for a while.

Why did changing the CPS take out the belt and tensioner? On my truck, I have a vacuum pump down on the bottom that was put on there aftermarket for a vacuum over hydraulic trailer brake setup. Do you have one of those on there?

Early '99 F350 DRW, Excab, LB. Auto. 2WD, 2010 bed, 2005 headlights, 298K, on my way to 1000K.
H2E, 238 Hybrids, Adrenaline oil, Tuned by Tony. DIY Regulated Return.
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post #4 of 52 (permalink) Old 03-01-2009, 05:25 PM Thread Starter
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Re: Random miss - can't figure it out

Thanks, I'll give it a shot.

I removed the belt thinking it would be easier to get at the CPS (wasn't much).

When I went to replace the belt, the tensioner broke off axis as I was reinstalling it. I didn't notice it at the time, but the belt shredded a couple days later....
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post #5 of 52 (permalink) Old 03-01-2009, 07:44 PM
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Re: Random miss - can't figure it out

the poppet valves within the injectors are toast.

typical symptoms are hard starting & runs rough cold, runs better hot...

take care~

Dave


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post #6 of 52 (permalink) Old 03-01-2009, 08:29 PM
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Re: Random miss - can't figure it out

Mine had a random miss at idle. Try unplugging the ICP sensor while the truck is running, that may cure your problem. Also check to see if you have oil underneath connector of sensor, this usually indicates a bad sensor.

2000 PSD Crew cab, Auto, 4WD, Elite Diesel chip
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post #7 of 52 (permalink) Old 03-02-2009, 01:50 AM Thread Starter
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Re: Random miss - can't figure it out

Quote:
Originally Posted by Mr. Jimmy View Post
Mine had a random miss at idle. Try unplugging the ICP sensor while the truck is running, that may cure your problem. Also check to see if you have oil underneath connector of sensor, this usually indicates a bad sensor.
Okay....did seafoam treatment- no change (fuel filter and bowl was clean as a whistle by the way so it looks like the fuel is okay)

Unplugged ICP - brief jump in RPM, resettled and have the exact same miss.

If I give it slight throttle, the miss will appear to go away at 1000RPM....the second I ease off the throttle in the slightest (say I drop to 900 RPM) it will miss and then run reasonably steady. As it idles around 600, it will miss about once/ 2 seconds. 750 is around once/ 3 or 4 seconds.

I'm currently uploading a video to photobucket so I can show the miss.....

I figure I'll take it to the stealership to have them check fuel pressure before I bit the bullet and get a set of injectors
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post #8 of 52 (permalink) Old 03-02-2009, 01:52 AM
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Re: Random miss - can't figure it out

Can you get a video with sound of your truck? That might be helpful.

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post #9 of 52 (permalink) Old 03-02-2009, 02:48 AM Thread Starter
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Re: Random miss - can't figure it out

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post #10 of 52 (permalink) Old 03-02-2009, 04:07 AM Thread Starter
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Re: Random miss - can't figure it out

More info. I noticed today that it doesn't miss on start-up....unless the engine is still HOT. IE if I shut it down and leave it for an hour, it will start right up and run great for about 10 minutes....then it will start to miss again.

I drove it from my house about 30 miles to a park....ran great. Had a picnic with the fam for a couple hours and it started up great and ran smooth until I hit the offramp near the house. When I stopped at the light, it was missing again. The only difference between the trip out and trip back was that I limited my speed to 60 on the way there.....and went up to 70 on the way back. Don't know why that seems to matter....
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