View Full Version : strange idle

05-10-2015, 01:32 PM
For some time now My sprinter has this no start when hot or rather extended cranking when hot episodes but not always when hot. With the highers temperatures this week it has done it a little more but I also noticed the idle goes up and down, not enough for the tach to show it but I can hear it. Can do it when I just started it cold or hot and some times at a red light but it will go away and come back on the same trip, once I give it throttle to move forward it will be gone but may do it again when at idle, kind of annoying. I have done injector tests several times and they do leak some fuel but not enough to condemn them as in less than 5/8". Can anyone shed some light or thoughts on this? Thanks.

05-10-2015, 03:41 PM
You beat me to it; my same issue years ago was a bad/failing injector. Have you tried the leak off test on a hot engine?
I would suspect low rail pressure due to injector, rail solenoid o-rings, maybe HP pump. If you have way of measuring the rail pressure, that might help. Rail pressure sensor might also be failing or have corroded wires.

other stuff:

check crank sensor for damage or clearance
check cam sensor wiring
check intake air temp and ambient temp sensors

05-10-2015, 04:32 PM
No codes for any of this, with the STAR scanner, did the injector test on a hot engine and same results though there is one injector out of the five that was changed at some point and the part number shows it is for a different sprinter year yet this was not an issue for the first year I owned the sprinter only after that and the injector was there long before I bough it.
I have new rings on the solenoid and also pulled the pressure sensor and put a new seal there as well and all wires look great with the insulation still in good condition, I will see the rail pressure though. I do not have a code for HP pump either but I would have to see if I can test that with My scanner.
Crank sensor is provably original so I will have to check that, cam sensor is new installed to rule out the old one, wiring is fine too. The intake temp sensor is is new, the ambient air temp sensor is hanging on the front, I can't find the slot where it is supposed to clip on. I will try this next too.

Thanks Bill.

05-10-2015, 06:17 PM
Ambient temp sensor is checked by looking at the temp instead of the clock, and if it's wildly out of synch with what you know the outside temp to be (reading 120 when it's 50 outside, etc). It clips in the hole in the plastic "bumper" behind the license plate.
I didn't have any codes when my van was doing this, either.
What I discovered is that the hot fuel is thinner, and can escape back in to the return fuel system easier. Either from a slightly clogged injector or something attached the fuel rail. There may be a possibility that it's the HP pump, though. Or wiring.

05-10-2015, 07:18 PM
I had this problem before and it continued even after replacing the HP pump (was leaking during cold weather) and clear fuel lines that were old and leaking. I was worried about leaking injector also.

Sprinter mechanic found rubber hose from fuel tank to filter had a small split at the hose clamp. Problem solved.

05-10-2015, 11:23 PM
You've got a STAR scanner? Can it do an injection quantity (or something similar) test? The leak off test only measures for one type of injector malfunction, there are others. See what else you can measure and see if one injector seems more out of spec than the others.

05-11-2015, 12:44 AM
Yes it is the xentry star scanner, I did the injector test with some time ago and it did show #3 different than all the others, #3 is also the only one with a different part # than the other injectors.
I've traced all the lines but the one going to the fuel tank, I should provably look at that too. The engine starts right away the first time then it may or may not do the extended cranking, some times it does it every time after it is warm.

I will do what You guys suggested and report back. Thanks.

05-13-2015, 12:20 PM
On mine, the idle would go up and down on cold start, so may not be the fuel hose.