Jim Warman Posted July 30, 2006 Share Posted July 30, 2006 Had an 03 in the other day... CEL is on and had a couple of concerns.... Some EGR related stuff that appears to have been cured with a MAF (old one had a lovely fur coat) but had a recurring P2285 - ICP low or something to that effect. Several road tests later, with nothing noticed on the IDS, I found the concern. Out of the corner of my eye, I noticed that the ICP PSI would respond on start up and track ICP desired but ICP volts would hang at 0 for a second or so. Remembering that ICP volts is a sensor value and ICP pressure is a computed value, I replaced the ICP sensor - problem gone... I could have spent the whole week looking for something that happened briefly at start up.... Quote Link to comment Share on other sites More sharing options...
jaysonfordtech Posted July 30, 2006 Share Posted July 30, 2006 I had the same thing, called hotline after capturing it on ids. I was advised to replace the connector and the sensor, as they were both updated. I was working with a 2003 f series. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted July 31, 2006 Share Posted July 31, 2006 Jim I guess those old eyes are sharper than you give them credit for? /forums/images/%%GRAEMLIN_URL%%/smirk.gif Makes you feel like a genius when you stumble onto something like this doesn't it? Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted August 2, 2006 Author Share Posted August 2, 2006 Not like a genius.. it just reaffirms that we can't rest on our laurels... not for an instant. In my case, the truck started every time... started real good. The PCM is making too many decisions to make life easy.... My take on this case.... the last time the truck was started, the truck started... PCM saw 0 volts and decided that this was probably wrong and substituted a PSI computed value. In spite of the 0 reading, the PCM allowed injector operation and there was sufficient actual pressure for the engine to start. Of course, the volts reading was way out of line and that set the code. Now, I'm all for "fail safe" operating but this is something that could have been added to the introduction section for the PPT. THEY know the PCM strategy... THEY should be able to give us better hints for some of this stuff..... Don't mind me... I have a new hire that the DP enticed into the flock..... He's not getting what he thought he was getting and I'm not getting what I thought I was getting. I can't avoid recounting this experience so keep an eye on the "water cooler" for the next few days.... I'm gonna let it build for a while.... Quote Link to comment Share on other sites More sharing options...
HGM Posted August 2, 2006 Share Posted August 2, 2006 In my case, the truck started every time... started real good. The PCM is making too many decisions to make life easy.... My take on this case.... the last time the truck was started, the truck started... PCM saw 0 volts and decided that this was probably wrong and substituted a PSI computed value. In spite of the 0 reading, the PCM allowed injector operation and there was sufficient actual pressure for the engine to start. Of course, the volts reading was way out of line and that set the code. Now, I'm all for "fail safe" operating but this is something that could have been added to the introduction section for the PPT. THEY know the PCM strategy... THEY should be able to give us better hints for some of this stuff ..... Jim,Its been in the strategy since the '94 PS to give a default value for the ICP.. Is this what your refering to? When the PCM sees an open circuit in the ICP harness, it will substitute a 725PSI(7.3)and 850PSI(6.0L) reading, if I remember the numbers correctly..From there it will use the AP to give an idea where the ICP should be.. Sometimes we miss stuff, it happens... I may be wrong as to what you're describing though, so maybe this will be of some info to guys that arent aware of this strategy.. PS, glad you found it!! /forums/images/%%GRAEMLIN_URL%%/laugh.gif Quote Link to comment Share on other sites More sharing options...
CERTIFIEDFORDTEC Posted August 4, 2006 Share Posted August 4, 2006 Good reason to check icp voltage and psi together. i once was stung on 7.3 where it went to the default of 725... not sure what is on a 6.0 Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted August 4, 2006 Author Share Posted August 4, 2006 I realize that an open circuit reading will develop a default reading.... but, usually, an open circuit will show up when we check sensor bias... something I did right at the beginning - IIRC, I had 0.18 volt - didn't look at the spec but I recall this is about borderline low. Think about the chain of events in what you expect for readings.... Select the PIDs, look at KOEO values - they're OK... start the truck and look for something after that. For me, engaging the starter somehow dragged ICP volts low (to 0) and they remained there for a short period of time generating the code. Don't forget, I wasn't tackling a running concern, I was tackling a recurring code... HGM.... you are right about advising some of the less experienced members on strategy.... Something I keep forgetting involves more PID data readings. A real good example is a shorted O2 heater...... If an O2 heater somehow shorts to O2 SIG, the scan tool will display 1.5 volts. It does this because that's all it is programmed for. If O2 SIG reads 1.4 volts, it will display 1.4 volts... if it reads 1.5 volts, it will display 1.5 volts...if it reads 12 volts, it will display 1.5 volts because that is all it knows.... Sherlock Holmes, step aside.... Quote Link to comment Share on other sites More sharing options...
HGM Posted August 4, 2006 Share Posted August 4, 2006 I realize that an open circuit reading will develop a default reading.... but, usually, an open circuit will show up when we check sensor bias... something I did right at the beginning - IIRC, I had 0.18 volt - didn't look at the spec but I recall this is about borderline low. Think about the chain of events in what you expect for readings.... Select the PIDs, look at KOEO values - they're OK... start the truck and look for something after that. For me, engaging the starter somehow dragged ICP volts low (to 0) and they remained there for a short period of time generating the code. Don't forget, I wasn't tackling a running concern, I was tackling a recurring code... HGM.... you are right about advising some of the less experienced members on strategy.... Something I keep forgetting involves more PID data readings. A real good example is a shorted O2 heater...... If an O2 heater somehow shorts to O2 SIG, the scan tool will display 1.5 volts. It does this because that's all it is programmed for. If O2 SIG reads 1.4 volts, it will display 1.4 volts... if it reads 1.5 volts, it will display 1.5 volts...if it reads 12 volts, it will display 1.5 volts because that is all it knows.... Sherlock Holmes, step aside.... Good points, this provides a good reason to look at the voltage PIDs as well as the pressure PIDS.. As you stated before, the voltage is the actual reading and the pressure is the processors interpretation filteresd and delivered to the scan tool.. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted August 4, 2006 Share Posted August 4, 2006 In addition to this, I've seen stuck IPR's on 7.3s that wouldn't set a P1212, and open IPR circuits that wouldn't set a code. This is a bastard to diagnose when the IPR connector is damaged. I unplugged the CMP on a 7.3 and it wouldn't set a code cranking. It seems the more you know about these beasts, the more you inaccuracies you find. The calculated ICP pressure really fools a lot of guys, you gotta look at voltage. When it's cranking, the ICP pressure will climb to 1200+ just like a normal truck..... Quote Link to comment Share on other sites More sharing options...
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