91 300D 2.5. Wont Go Over 2,000 rpms! - Page 2 - PeachParts Mercedes-Benz Forum

pmckechnie · #16 09-02-2012, 04:58 PM

With the shifter in D the transmission may be up shifting too soon which would make it feel sluggish. If it seems to have more power by manually changing the gears then the governor is the place to start. If you take the car out on an interstate where you can run it a higher speed the governor may clean itself out. You will know if the governor has corrected itself when you can shift from N to R with the engine running and car stopped.

A boost gauge would be great to have for trouble shooting boost problems. I found one at AutoZone that was about 1 in diameter for about $15 if I remember correctly. I put it in temporally about 7 years ago and it is still there.

Paul

JamesDean · #17 09-02-2012, 07:06 PM

OK

ON THE TURBO FRONT:

So I bought a boost gauge from the local parts store ($25

)

I Y'd the boost gauge into the boost circuit with the wastegate and other vacuum things hooked up stock. Nothing. No boost once so ever, no matter the RPM. I was parked in the driveway during testing. I didnt feel like running the gauge into the cabin.

Next I connected the wastegate actuator to the vacuum supply on that side and tried again. This time I was able to achieve a whopping 5 PSI...AT 4K+ RPM. What is normal pressure on this turbo? I do not know. I believe someone said 30 psi, with wastegate fully actuated?

Either my wastegate actuator does not FULLY actuate or my gauge / plumbing is ****ty.

ON THE TRANSMISSION FRONT:

I cannot seem to find first gear.

A) My kickdown switch does not seem to be functioning. Either it is not connected or the wiring at the back of the transmission is compromised.

B) Even with the selector in "2" from a dead stop, I cannot seem to get into first gear

This leads me to believe the governor is sticking (or perhaps not fully inserted?) and the transmission must exert more force to spin the governor causing the governor to output more pressure/fluid than normal and thus put the transmission into second gear.

The governor is also preventing me from shifting from N->R/P without turning off the car. I took the car for a 30-40 mile highway trip and there was no change in governor behavior.

I think if first gear was operable that I would perhaps not notice the low power output of the turbo. But now that I am stuck starting in second gear without access to first gear... the weakened turbo is much more evident.

The car worked perfectly fine on my first test drive post governor/driveshaft/exhaust re-installation. It pulled nicely and shifted well.

What's Next?

I am open to additional thoughts, ideas, tests and anything you guys can come up with. I think sometime in the week I'll kick it to my mechanic to make sure the engine side of things is working properly, if it is not.. to the pressure regulated wastegate setup I go.

As for the transmission... I was hoping the drive would clean/fix the governor. I dont want to go under there again. I was contemplating phoning a local transmission shop to get quotes. I know that I'll be back under the car after I hear their numbers.

pmckechnie · #18 09-02-2012, 08:18 PM

To get boost, you have to have the engine under load. You have to drive it to get it under load at 2500rpm+. I am not sure how much boost you will have. I forget things after 7 years but I know my 91 300D will make 15 lbs at 2000 rpm if pulling hard. That is where the wastegate takes over.
The governor being stuck could prevent 1st gear start, so that issue needs attention first.

Paul

JamesDean · #19 09-02-2012, 08:30 PM

Quote:

Originally Posted by pmckechnie

To get boost, you have to have the engine under load. You have to drive it to get it under load at 2500rpm+. I am not sure how much boost you will have. I forget things after 7 years but I know my 91 300D will make 15 lbs at 2000 rpm if pulling hard. That is where the wastegate takes over.
The governor being stuck could prevent 1st gear start, so that issue needs attention first.

Paul

AH! That makes more sense. I'll have to plumb the boost gauge into the cabin and check my boost numbers again. I knew they were odd. Especially when my 617 showed relatively the same numbers.

sixto · #20 09-02-2012, 10:33 PM

Can you force first gear by setting the shift lever to 2 at a full stop then applying throttle with your foot still firmly on the brake pedal? Slowly release the brake pedal without backing off the throttle pedal and see if you've found first gear. You'll overheat the transmission fluid if you do this, I think it's called power braking, for more than a few seconds.

I don't know if this is something you should try given the situation with your transmission. In might in fact make things a lot worse.

Sixto
87 300D

compress ignite · #21 09-03-2012, 01:40 AM

Place Transmission Selector Lever in #2, then back up to #3,then back to #2
"Crisply" and FULLY DePress the "Right hand Foot Pedal".

If "IT" cannot "Find" 1st:

"Kickdown" is Bad
OR
Internals (Such as,Valve body,Etc.) are in need of attention.

JamesDean · #22 09-03-2012, 12:48 PM

Update:

Turbo Front:
I hooked up the boost gauge to a port on the side of the intake manifold. I was pleasantly surprised when the boost gauge kit had appropriate connectors for the fitting!

I ran the gauge into my window and drove the car with the stock vacuum setup on the transducers.

Nothing. 0 boost.

I bypassed the transducers and connected the vac supply right up to the wastegate actuator. Drove again.

I started making boost at about 1800-2k rpm. It seemed to peak out at about 15-17 psi if my gauge is to be believed. I thought I read 30 psi should be what it makes at peak so perhaps my wastegate actuator is not fully actuating at this point in time.

Furthermore something must be throwing a code causing the EDS to cut boost in the stock setup.

Will have to pull codes and see. Otherwise its a wastegate conversion for me.

Trans Front

I found a parking lot, stuck the shifting in to 2, then 3, then 2, then punched the pedal. Still no first gear. Governor still appears to be dirty/sticking as I cannot get it to shift from D-> P without turning off the engine. I am curious if that is connected to the lack of first gear. I.E The governor pressure is forcing the transmission into second.

I dont think kickdown is working either. Not sure if that is electrical or internal to the transmission, perhaps regulator pressure is overriding kickdown solenoid's influence on the transmission...

sixto · #23 09-03-2012, 01:46 PM

Most folks see max boost in the 12-14 psi range with a pressure actuated wastegate. Since you have no wastegate effectively, I'd expect up to 18 psi but I wouldn't hold it there for more than a couple of seconds. 30 psi will melt valves given the fueling limitations of your IP! It sounds like you're good for max boost but it's coming in late if the gauge indicator doesn't lift from 0 until 1800 rpm under full throttle. I'd expect about 5 psi at 2000 rpm with everything in by 2500 rpm. A properly tuned engine goes from 2000 to 2500 rpm pretty quickly under full throttle making it difficult to read the tach and a boost gauge simultaneously.

Sixto
87 300D

JamesDean · #24 09-03-2012, 03:10 PM

Quote:

Originally Posted by sixto

Most folks see max boost in the 12-14 psi range with a pressure actuated wastegate. Since you have no wastegate effectively, I'd expect up to 18 psi but I wouldn't hold it there for more than a couple of seconds. 30 psi will melt valves given the fueling limitations of your IP! It sounds like you're good for max boost but it's coming in late if the gauge indicator doesn't lift from 0 until 1800 rpm under full throttle. I'd expect about 5 psi at 2000 rpm with everything in by 2500 rpm. A properly tuned engine goes from 2000 to 2500 rpm pretty quickly under full throttle making it difficult to read the tach and a boost gauge simultaneously.

Sixto
87 300D

I did see 5psi by 2000 rpm. Don't recall seeing everything by 2500 rpm.

Perhaps the wastegate actuator is not fully opening the wastagate?

sixto · #25 09-03-2012, 03:16 PM

You mean closing?

Sixto
87 300D

JamesDean · #26 09-03-2012, 03:20 PM

Quote:

Originally Posted by sixto

You mean closing?

Sixto
87 300D

Yes. I had it backwards. It could also be my gauge. I think there is a small deformed section in the line going to it.

JamesDean · #27 09-03-2012, 03:37 PM

Furthermore:

Let's assume my transmission is starting in second when it should start in first.

How would this effect EDS turbo control?

EDS will throw code 14 when the pressure sensor does not see boost (of some 500mBar (7psi) and (in theory) shutdown all turbo operations.

Could starting out in second gear cause the turbo/wastegate system to act odd and fault out?

sixto · #28 09-03-2012, 04:22 PM

EDS isn't that smart. It doesn't know what gear you're in or how fast you're going. Only engine rpm and control rod sensor position as a surrogate for engine load. I don't think the overboost solenoid, if you car has one, is tied into EDS. Later 2.5s have a MAP sensor. Maybe all 2.5s have a MAP sensor.

Sixto
87 300D

JamesDean · #29 09-03-2012, 04:46 PM

Quote:

Originally Posted by sixto

EDS isn't that smart. It doesn't know what gear you're in or how fast you're going. Only engine rpm and control rod sensor position as a surrogate for engine load. I don't think the overboost solenoid, if you car has one, is tied into EDS. Later 2.5s have a MAP sensor. Maybe all 2.5s have a MAP sensor.

Sixto
87 300D

I'm not saying EDS is doing this. I recall coming across something in the EDS testing that the pressure sensor should see 500mBar of pressure @ X rpm. If it does not, then it throws fault and kills boost.

I was curious if starting out in second gear like my transmission is currently doing is effecting the turbos ability to produce boost and thus faulting out the EDS causing it to cut boost.

It was just a thought, I'll have to go back through.

sixto · #30 09-03-2012, 04:59 PM

I doubt starting in second makes any difference to EDS. Load drives production of boost. RPM is a byproduct.

Sixto
87 300D