Pablo wrote:
I am sorry, but there exists much needless confusion on this site about "Limp mode". Waaay long time ago, somebody started calling all trans and fuel issues "limp" mode and the misnomer stuck.
Limp mode always sets a code. A code scanner is a few bucks at harbor freight or checker or whereever. I would have a really hard time believing that limp mode was triggered and the check engine light (CEL) was not thrown. Anyway, if no code can be read with a scanner... it was not limp mode. If the computer for any reason disables power, it does so to protect mechanical equipment and always sets a code.
If there is no code set, this is likely caused by a lack of fuel.
It causes THE EXACT ISSUE described by the OP. I know because I have had it happen to me. I have had a batch of bio left in the tank for 3 weeks (I parked it and let it sit) that went bad... the result was first a little loss of power and some hesitation after heavy throttle... then as the filter became plugged with crap from the tank... this exact behavior. It would hardly go. Pull over, restart... good to go. Then it would rev fine but would not upshift. Letting off the fuel pedal caused "coughing and spitting". No Cell thrown, no codes set that could be read.
Changing the filter stopped my issues for about a week at a time... but the tank had sludge on the bottom of it now. After going through four filters in a month, I said to hell with it and dropped the tank and flushed a bunch of yucky sludge that had formed out of the bottom of it. All has been well since. Now I only add bio when I am going on a trip or driving every day. Take a fuel sample, change the filter.... but whatever this is, it is likely not a computer induced condition (not without a code set).
Actually this is not altogether correct. I have definatly had "limp mode" occur without the computer tripping a CEL. I don't know why the ECU would cause a limp mode without a CEL or DTC because it goes against all conventional wisdom about ECU functioning, but then again, there are many things about the CRD which go against conventional wisdom. I have had it occur from a plugged fuel filter the same as you, but the CEL didn't show up until 3 or 4 occurences of the limp happening while driving. It would be triggered initially by fuel starvation under acceleration up a hill, with a stumble or two. If I let off of the accelerator so that it could get enough fuel but still kept it in high gear, the drivability remained fine, but as soon as I dropped down into the lower range, the limp feature was initiated and I had to wind up almost to redline, then back off the accelerator, in order for it to shift up. After restarting it the limp would clear until the next time it happened. after doing this several times at will the Cel came on and the scanner could read a P0093 DTC. Untill the CEL was thrown, there was no DTC shown on the scanner. I have also had the same power loss from a restricted filter which you described, a couple of times but it didn't trip the limp mode or CEL on those occasions for some reason.
On another occasion it started missing really badly shortly after plugging the MAF in after several months of running with the ORM. It went into classic limp mode with the impaired shifting, again with no code or CEL. After restarting it ran fine the rest of the morning, but did it again that afternoon, but that time it lit the CEL and gave me a 0401 EGR code along with another I had never seen, I don't remember the number but it said "random engine miss". My theory was that the EGR stuck open and caused the miss. After a good hot Italian tune up, it never did it again.
Both of these occurences were definetly limp modes which were ECU induced and happened without the CEL being tripped. Strange as that may seem.