How much boost should I see on a '98 E300 turbodiesel, bone stock? T'd into the map sensor hose, I'm only seeing 5.5 psi on a customers car. Seems low, but I can't find any documentation even in the service manual.

Subscribed .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

That definitely seems low. The 603 stock level was right around 13PSI, I'd expect the 606 to be the same or even higher since it has an intercooler.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Before doing anything else, it's time to take apart, test and clean the entire boost pressure sensing system ~ I've found most to be at least partially blocked, the over boost relay is often clogged closed or nearly so and easy to clean every part by blowing ether (starting fluid) through after swapping the dispensing nozzle for one that will hold the little plastic straw .

DO NOT use carby or brake cleaner ! these will attack the plastic and rubber bits, cau$ing you issues sooner than later .

Let us know what you find and do to correct it .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thanks for that. FWIW, it's had the vacuum solenoid for wastegate control replaced by another shop. If I test vacuum there with it running, it has a strong ~26 in/HG, so I know our vacuum source works well. Wastegate actuator works as it should, and holds vacuum without leaks.

What should we be cleaning? The EGR mixing chamber part?


For reference, I just took my car out with the gauge (sadly, the only boost gauge I have at the moment only goes to 10 psi), but my car (stock, plus Rocketchips Stage 2 ECU tune) pegs the gauge at ~30% throttle, soooo..... I think we definitely have a boost problem.

Stock boost pressure Max is 15 psi sometimes if will creep to 15.5 but that's when the internal waste gate opens up. My MAP sensor did read low for a bit, cleaned it out with MAF cleaner and also make sure the hose is not clogged that comes off the EGR, it likely will be.

__________________
1999 E300D OM606, 278,000 km (Daily)
1984 Camry Turbo-D, 319,000 mi (Sold)
1992 300D OM602, ~450,000 mi (Sold, Blown Head)
1999 F250 7.3 Powerstroke, 243,000 mi (Sold)
1996 VW Passat TDI 110,000 mi (Sold) "The first Diesel"

I just thought I'd update everybody (nobody ever does lol). Found the vacuum line to the MAP sensor had a slide in it near the mixture chamber. Replaced the vacuum line, and 100% better. It's always something small and dumb. Thanks everybody!

Just to be clear, the line between the manifold and the MAP is not a vacuum line, it is a pressure line. Be sure to install either the factory clips or a zip tie on each end to keep the hose from blowing off the barb.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

It usually is a simple thing, remember : K.I.S.S. ! .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better