2003 T1N won't rev past 3500rpm

[Alexidoid]

I recently purchased a 2003 T1N with about 240k miles. I've since driven it about 1800 miles without any major issues. It's been a little gutless on hills but will do 80mph on the highway no problem. Only thing that isn't standard is a cheapo low pressure fuel pump hooked up inline right before the fuel filter connected to a toggle switch on the dash. Haven't had an issue with fuel or the clogged fuel filter light unless I forget to switch the pump on

I've been going through everything doing standard maintenance and after replacing the fuel filter today realized that it won't rev past 3500 rpm in neutral. I've read about 3000 rpm limit for limp home mode etc. but haven't seen anything specific about a hard limit at 3500 rpm. First thought is that the fuel pump can't keep up with demand after 3500 rpm, but the cutoff is so sharp that I'm questioning that assumption.

I've linked a video of the engine slowly being rev'd up to 3500 rpm. The turbo whine is barely audible on the second run and seems to suddenly cut off a little under 3500 rpm.

If this is a common problem and I'm failing to find it through search, I apologize

 

[Alexidoid]

Or maybe my tach is miscalibrated

 

[Cheyenne]

It sounds like you have disturbed the vacuum line somewhere on its way to the turbo actuator. This is exactly what mine does if I forget to reconnect at the brake booster after replacing the air filter.

Check the connection at the brake booster, solenoid valve below the air filter, turbo actuator and (most importantly) the recirc solenoid on the heater air intake plenum.

Keith.

 

[Midwestdrifter]

Do you have a scanner with live data capability? That's the single best tool you can have. That will let you monitor boost levels, confirm gauge readings, etc.

 

[hkpierce]

No diagnosis - but turned out that mine with similar can-do-80-but-trouble-higher-rpms turned out to be a marginal #5 injector.

 

[Alexidoid]

Do you have a scanner with live data capability? That's the single best tool you can have. That will let you monitor boost levels, confirm gauge readings, etc.

I picked up an Autel MD808P and have some more info that may help.

Haven't found any engine codes.
Confirmed that engine won't rev past ~3580 rpm. It's quite exact. Doesn't seem to matter if the engine is cold or warmed up. I do get a slight bouncing idle between 660 - 700, but it goes away shortly after the engine starts.

I'm still learning how to use the scanner, but I was able to get a live MAP reading:

I'm at sea level, and this is all taken while parked.

at 680 rpm - MAP ~14.7
at ~3500 rpm - MAP ~17
at ~3580 (the mystery limit) - MAP ~ 16

This is with almost no LOD.

Are there any other numbers I should be looking at specifically that could be a good indicator of the problem?

 

[Alexidoid]

@MillionMileSprinter, I was just watching one of your youtube videos and noticed that the little green fuel pump featured is the same one that a previous owner put inline right before the fuel filter in my T1N.

Do you run these inline permanently or just to prime / pressure test the fuel system?

If they're permanently installed have you ever had an issue with restricted fuel flow that could limit engine rpm?

 

[Alexidoid]

It's been resolved.

Scanner eventually picked up a code P1188 - element shut of high pressure pump... that lead me to this thread: https://sprinter-source.com/forums/index.php?threads/14632/

I checked the connection to the shut-off solenoid on the HPP. The plastic plug was cracked and backed out about a 1/4 inch. Pushing it back in immediately solved the problem.

To recap the symptoms I was experiencing:

• Wouldn't rev past 3500 rpm
• Gutless on hills but would hit 80mph on flat no problem
• Very very delayed downshifting

It looks like the HPP solenoid connector is tied directly into the wiring harness. Right now I'm planning to cut off the old connector and solder a new one in.

Is there a better option for replacement?