STROKER_T Posted December 5, 2008 Share Posted December 5, 2008 Got a '99 F550 tow truck thats been all over town for an idle concern,so here goes: The truck runs OK,slight miss on #3 cylinder,has good fuel pressure at the pump.When you rev the engine and it comes back down,it sounds identical to a V8 gas motor with a radical cam...after about 10 seconds the idle starts to smooth out,only noticing the injector miss. In the past I have fixed this concern with an IPR valve or a simple oil change...not this time! I'm wondering if the check valves at the heads could cause this concern,or maybe a fuel pressure regulator... I have only replaced the IPR at this point,wanted to get yall's perspective.The oil is fresh,the engine only has 112K,in the past 2 months other shops have replaced the IDM,ICP sensor,a few injectors,cam sensor...i think thats it My understanding is that the IPR controls the idle,what am I missing?It does it hot or cold and only when RPM's come back down to idle,and only for a short time.I was convinced that the IPR valve would fix it,but i was wrong...ouch Anybody got any ideas? This customer has dropped 3000 dollars elsewhere for the same concern,now all of a sudden he's on a budget... Quote Link to comment Share on other sites More sharing options...
STROKER_T Posted December 6, 2008 Author Share Posted December 6, 2008 Got to work on this beast this mornin',found that the idle smooths out when ICP sensor is disconnected,but the funny thing is the ICP pressure PID reads zero psi...shouldn't it read 725 (default mode) disconnected with the engine running? Does it make a difference being a manual trans? According to the PCED,the ICP sensor should be replaced if the engine starts with the sensor disconnected...huh? This engine starts ,swapped out already new sensor with a known good one, no change...I'm beginning to think i got a pcm or vref issue,vref reads 5.0. Anyone got any ideas? /forums/images/%%GRAEMLIN_URL%%/popcorn.gif Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted December 6, 2008 Share Posted December 6, 2008 Got to work on this beast this mornin',found that the idle smooths out when ICP sensor is disconnected,but the funny thing is the ICP pressure PID reads zero psi...shouldn't it read 725 (default mode) disconnected with the engine running? Yes, normally. I think the Gen 1's defaulted to 425 and Gen 2's 725. Does it make a difference being a manual trans? No. According to the PCED,the ICP sensor should be replaced if the engine starts with the sensor disconnected...huh? Brother.... This engine starts ,swapped out already new sensor with a known good one, no change...I'm beginning to think i got a pcm or vref issue,vref reads 5.0. Anyone got any ideas? /forums/images/%%GRAEMLIN_URL%%/popcorn.gif Did you check and clear DTC's? What came back? What's the signal voltage in scan data? What's it ready physically at the ICP? Three wires, VREF, ground (Ford calls ground "signal return" /forums/images/%%GRAEMLIN_URL%%/scratchhead.gif) and signal. The voltages are the same as 6.0 (and this is misprinted in the WSM also) KOEO .17-.24v, idling near .8v. I think the WSM shows it as .02v KOEO instead of .2v. What's IPR command? It should be 15%ish at a cold idle, and 9-11% at a hot idle. I'd look at scan data first, then backprobe the ICP and read voltages on all three wires. Ground should be damn near 0v- maybe .05 max or so. If the voltages check out OK, force some DTC's by unplugging stuff and make sure codes can set and clear. You should have had a hard P012XX with the ICP unhooked. If things don't add up, put a breakout box on it and check all power and ground voltages against the battery negative terminal while its running. Good Luck! /forums/images/%%GRAEMLIN_URL%%/grin.gif Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted December 7, 2008 Share Posted December 7, 2008 I think you will find that there are conditions that need to be set before your scan tool will display the default ICP reading. Unplugging the sensor with the key on will not provie this on it's own.... Remember that this is a vague memory but I am reasonably sure that at least one key cycle (or start cycle) with a "bad" ICP reading is going to be required. Is a cylinder contribution test any help? I can't remember if that one has the test available (there are very few 7.3s left in our area) - if not how about an injector kill box. Does the engine seem to have a "regular" miss or is it more random in nature? You state that fuel pressure is good while this is going on so I feel that you shouild be able to rule out the base fuel pressure regulator. When you rev the engine up, is there an unexplained skip around the 1700~2000 mark? I've seen this a lot when injector O-rings are getting to the end of their service life... That "slight miss" on #3 would be gathering some of my attention, too... up until I had something concrete I could blame it on. I know I keep harping on about basics... One or more other techs have looked at this truck... those techs did not discover the cause of the concern.... Whenever I am given something that "can't be fixed", I usually find something that got overlooked or under-appreciated. Having said that, I am assuming that the truck has passed the oil aeration and low idle stability tests? Bruce... I am beginning to think that SIG_RTN is Fordese for "dedicated ground... with a splice in a bad place". Just to add to your post.... it is important to make ones first volt measurement a "baseline". Whether our electrical testing is done KOEO or KOER, we desparately need to know what our base voltage is in the appropriate case and we need to make sure that we are "in the park" at various times through our testing. I've watched techs trying to test volt drops with battery voltage < 9VDC. FWIW, Ma Ford will tell you.... the only good ground for test purposes is B-... the only good power source is B+.... works. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted December 7, 2008 Share Posted December 7, 2008 AKKKKK!!! And Bruce and I both missd mentioning looking at sensor volts rather than the computed PSI reading.... Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted December 8, 2008 Share Posted December 8, 2008 AKKKKK!!! And Bruce and I both missd mentioning looking at sensor volts rather than the computed PSI reading.... Huh? You "flate rate reading" again? /forums/images/%%GRAEMLIN_URL%%/grin.gif Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted December 8, 2008 Share Posted December 8, 2008 Originally Posted By: Jim Warman AKKKKK!!! And Bruce and I both missd mentioning looking at sensor volts rather than the computed PSI reading.... Huh? You "flate rate reading" again? /forums/images/%%GRAEMLIN_URL%%/grin.gif Whoops... apparently... Quote Link to comment Share on other sites More sharing options...
STROKER_T Posted December 8, 2008 Author Share Posted December 8, 2008 Thanks Bruce and Jim for your insight...did as you both advised and voltages /pressures check out,but with breakout box connected pin 87 has O.L. ohms at pin 103,which directs me to replace PCM. Continuity is good on all 3 wires at ICP to PCM. Default pressure (725) never shows up on datalogger,dont know if I'm chasing nothing or not there,but the truck runs and idles good with ICP disconnected. Injector analyzer shows injectors 2-4 inop when cold,1-3-7 when warm,its got all 8 remans in it,but it looks like they've been there awhile,has original glow plugs that could cause that 2-4 issue... RPM is at 705-720 at idle,goes to 650 w/ icp unplugged.PCM has been out recently,part number checks out,its been updated twice. Should I be focusing on a mechanical issue or electrical/PCM problem?...PCED says replace PCM,but I dont know if I should trust it...i hear you laughing Really want to fix this thing,and i look forward to the occasional challenge,but this guys wanted his truck back yesterday...Thanks again for the help,this website is awesome! /forums/images/%%GRAEMLIN_URL%%/shrug.gif Quote Link to comment Share on other sites More sharing options...
STROKER_T Posted December 8, 2008 Author Share Posted December 8, 2008 I was wondering if it would be a good idea to block off one head at a time,and check for pressure difference...if i remember right,i think an ICP jumper connector has to be hooked up,cant find mine,been awhile since i had to dead head Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted December 9, 2008 Share Posted December 9, 2008 pin 87 has O.L. ohms at pin 103, I'm trying very hard to control myself.. I don't want to be a bad man. In your mind... what does "O.L. ohms mean". Bear with me... I wouldn't ask this if I hadn't seen a LOT of problems with the concept. I have seen techs think that OL (out of limit) means "no ohms"... just the same that a "real" zero resistance reading indicates "no ohms". Electrical is easy.... damned easy.... but nobody wants to let it be easy... We need to obfuscate the issue.... we need to add confusion where no confusion is to be had... we seem to be able to confuse infinite resistance with no resistance. I don't umderstand why... because electricity is the easiest, simplest thing you will ever need to understand. Whoops... sorry... another bad day. Think about what I said.... Electrical IS EASY. Grasping the concepts isn't hard.... Quote Link to comment Share on other sites More sharing options...
STROKER_T Posted December 9, 2008 Author Share Posted December 9, 2008 OK Jim,u caught me being stupid,I'll try not to let it happen too often.What I failed to mention was that the correlating pins all read 55K ohms,not a reliable test,i got it... So I ran a power and ground side test with the breakkout box,everything checks out below .05v.The truck is still not fixed,waiting on a PCM,goin' out on a limb with this one... Did a pressure differential check on the heads,no difference on fuel or oil.Tried a filter housing drain and fill with cetane booster to check for worn injectors,no change.Injector analyzer shows weak injectors,some hot,some cold.It's got a rough idle,tried to sell injectors,customer only wants the idle fixed only,what am I supposed to do,wave a magic wand at it?Harry Potter has it so easy... /forums/images/%%GRAEMLIN_URL%%/whattodo.gif Quote Link to comment Share on other sites More sharing options...
cbriggs Posted January 8, 2009 Share Posted January 8, 2009 If its a standard what kind of shape is the dual mass flywheel in? if it still has one? Quote Link to comment Share on other sites More sharing options...
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