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Random miss - can't figure it out

21K views 51 replies 11 participants last post by  TrailerHauler 
#1 ·
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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#3 ·
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?
 
#4 ·
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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#6 ·
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.
 
#7 ·
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 :doh:
 
#10 ·
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....
 
#11 ·
Look at the wiring going into the IPR, and at the connector itself. Some of these trucks have issues with fuel and oil damaging the insulation on the wiring. I've found it on my IPR connector and on a UVC harness connector.
 
#12 ·
Wiring looks good at least at the connectors until it goes into the plastic sheathing.

Here's a video from cold start-up to warm this morning. It was about 8:30AM


I started the truck again at around 3:00PM...cranked right up and ran great for about five minutes...then began missing. Ran that way for ten minutes....then stopped missing for a while...then did it again until I got home.

 
#17 · (Edited)
Sure thing!

Any probable reason why sometimes it starts like crap while other times starts just fine on cold start? Does a dead hole not cause an SES? I figured if it was worn injectors it would always behave in a similar manner from a cold start.....

And how bad have I screwed up my truck by driving it?
 
#18 ·
Sure thing!

Any probable reason why sometimes it starts like crap while other times starts just fine on cold start? Does a dead hole not cause an SES? I figured if it was worn injectors it would always behave in a similar manner from a cold start.....

And how bad have I screwed up my truck by driving it?
no, the only thing that will throw an SES light is a wiring (or electrical) problem with the PCM-IDM-Injector...

The PCM does not actively monitor injector (or cylinder) balance. It does however, actively monitor electrical continuity.

take care~

Dave
 
#19 ·
Keep this alive please!!!!!!!!!!!!!!

Please!!!! Keep this thread moving along with ALL and ANY information that you come up with concerning this truck's issues. I have similiar issues on my 550 and I am down to getting ready to replace #8 injector.

I have good starts but crappy cold power, I think a miss also. I can't really tell. Buzz on 8 is sometimes weak, like a towel is over it. The truck will run very well, but not all the time. Replaced drivers side uvch have tried different icm with no change.

Hud
 
#23 ·
I see your :confused: icon there Dave... Just hassling you a bit.

I know you remember me. The guy in Virginia with the 550 that had an injector not plugged up good.

I am still having an issue similiar to the one the starter of this post is dealing with. I think number 8 is my issue and I procured a good injector from a friend of mine. I am just hoping that replacing it will clear up my problem.

It bugs me to no end that I have one truck, 1995 with 300k miles, that runs so much better than a 99 with 220k AND has already had one set of injectors.

Just another day... If the trucks were not giving me problems it would just be somthing else I guess.

Seriously, I appreciate your knowledge and help.

Hud
 
#26 ·
Spoke to Dave before I took it to the dealer.....awaiting confirmation on the issue. The real question is....do I do these things one at a time as they fail....or just go through in a single sweep and replace them all? How would I know if any have already been replaced? Is it possible to know?

If I pull them all out to inspect them, as with most other seals, would I need to replace the O-rings or can they be re-used?
 
#27 ·
Unless you just replaced the orings real recently (in the last couple weeks), put a new set on. Lube with ample amounts of oil on reinstall.

On the inj that you're having trouble with, have you pulled the solenoid off and checked for a loose armature/poppet screw? If loose, it will shut down the injector down. Old injectors will get loose poppet screws and its a very easy thing to check and repair if loose.
 
#28 ·
Word is - P0275 #5 Cylinder Contribution fault.
That was the only code he pulled.

Wasn't able to speak directly with the service tech...so I don't know exactly what tests he ran. I know what I asked for, we'll see what he gave me.....

Dealer is also trying to say that blowby is excessive.....
According to my understanding of the the oil cap thumb rule....if you can place the cap upside down on the filler neck and it stays (aside from vibrating off) its fine... Anyone have anything to the contrary?
 
#29 ·
I would suggest you pull off your air intake tube (from the airbox to the turbo inlet)...and peek into the compressor housing and inspect the wheel for signs of damage.

Also take a close look at the air filter 'box' where the filter goes...if the tabs are broken, missing, and/or the spring clasps broken or missing, then things aren't looking too promising...inspect the inside of the intake tube for grit, sand, dirt, etc...though oil in that tube is perfectly normal from the crankcase vent that redirects the oily mist from the valve cover into the intake tract.

On the turbo...the outermost perimeter of the fins should be very nice & crisp right angles...if the outer perimeter of the fins are rounded, bent, "thinned", or sandblasted looking...then you probably need to have a compression test performed...prior to dropping x hundred bucks on an injector & installation.

but yes, excessive crank case pressure would lift the lid off of the oil filler neck...

take care~

Dave
 
#30 ·
When I originally Ohmed my GPs when I had hard start, the intake piping was pretty clean, and the compressor looked good. The tabs for the filter and springs were all in place when I replaced my filter not too long ago.....but I'll take a good look at all of it again.

For what they want to pull the valve covers off and check underneath (some 370 bucks) I'll buy a diesel kit for 80 bucks and do the compression test myself. I'm thinking the dead miss in conjunction with no smoke lends credence to a bad injector/harness. I've read a number of posts outlining a pretty good bit of white smoke when blowing unburt fuel out the exhaust....

Was this brought on by the excessive blow by comments?

The contribution fault seems to lend credence to a bad injector....especially if I get a SAT buzz test, right?
 
#32 ·
Did the buzz test confirm #5 also? If you are pulling the valve covers, I'd check for a loose poppet screw. It will give a funky buzz result and kill the injectors operation (almost like its turned off).

On your earlier belt question, the Gates interchange info notes a 122.3" belt.
 
#34 ·
The tech said he believed the test was SAT. But yeah....dealer is telling me the engine is dusted and I need a LB. I don't believe it yet.

I've asked for the measurement of the "excessive crankcase pressure" and the operating temp at which it was done.

I would think with a dead miss, and a low comp cylinder, I would see either a pretty good amount of white smoke in the exhaust or a heavy puffing oil filler neck. Is it possible to have a dead cylinder due to compression not exhibit either of these symptoms?

I'm going to pick up the truck this afternoon and examine the comp wheel as Dave said and pull the valve covers and hit the injectors with a feeler guage (as I read in another post to identify poppet wear). I guess I can do a Valve cover off test to check injector operation.

By the way....I told the dealer I was picking the truck up (ie you are not servicing my truck) and fifteen minutes later they called to tell me a power steering line burst while the tech was backing it out of the garage....repair cost 145 bucks......

I'll be posting more pics this evening or tomorrow morning to continue ts'ing
 
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