4.2L Dtronic Mercruiser

[Parker]

Hi - I'm new to the forum from the USA - please be gentle'

There is very limited help on forums in the US on these engines and I would appreciate any assistance from across the pond. On my engine and a few other engines of owners I have written, throttle response from idle (700RPM) to 1050RPM is abrupt. Upon gradual increase of the throttle position sensor lever the RPM jump from 700 to 1050 as soon as the LGS - low idle switch shuts off (LGS inside of TPS is non adjustable). LGS turns on and off at approximately 13% of total range of TPS lever. Ater many hours of troubleshooting and replacing parts the problem has not been solved. I think that this might be inherent in its design and has become more noticable due to installation of a digital tachometer and changing propellers from 26 to 22 inch pitch (less load). In forward gear the jump is from 700 to 950RPM. Owners of this model engine could you please tell me if this is normal . Any responses would be greatly appreciated.
Bill D.

 

[volvopaul]

There is a forum member called latestarter he will be able to help you im sure on this one.

 

[DAKA]

In forward gear the jump is from 700 to 950RPM. Owners of this model engine could you please tell me if this is normal . Any responses would be greatly appreciated.
Bill D.

Hi Bill and welcome

Hopefully Latestarter will be along soon with the technical response, in the mean time I have Twin Cummins-mercruiser D300 4.2L for the last 6 seasons running through Hurth ZF 63a on 22 inch X 26 inch pitch props and I have not noticed an issue except on one occasion the gear cable was slightly out of adjustment and I had to push it into gear as the throttle cable moved forwards.

On that occasion the revs increased as I engaged gear, usually I push the gear lever forward and the gear is silently engaged and the revs do not increase without further pressure on the lever.

Gear cable adjustment page 853 of the service manual, if you would like a pdf copy of the service manual feel free to pm me your email.

Regards
Pete

 

[Parker]

VolvoPaul and Daka thankyou for responding to my post.
The throttle linkage to the throttle position sensor is 100% O.K. This was checked using the Rhinda Scanner which indicated a range of 0% to 100% when moving the throttle lever and .39vdc to 3.39vdc (within acceptable range). Multimeter check- resistance of the tps potentiometer was 1112ohms to 1695ohms, and the LGS (low idle switch) turned on and off at 1185ohms. I was unfamilar with diesel tps's and thought they should operate similar to automobiles, that the low idle switch would turn on and off with little initial movement of the throttle pedal. Mine turned on/off at approximatley 13% of the throttle lever range. First misdiagnosis - new tps produced the same results' The tps has a non-adjustable LGS circuit, it has a printed circuit board with contact wiper arms. The tps potentiometer is also printed onto the same circuit board as the LGS. I would have thought the LGS would turn on/off at the lower end of the tps potentiometer resistance, like maybe 1120 ohms ?

 

[Latestarter1]

Hi - I'm new to the forum from the USA - please be gentle'

There is very limited help on forums in the US on these engines and I would appreciate any assistance from across the pond. On my engine and a few other engines of owners I have written, throttle response from idle (700RPM) to 1050RPM is abrupt. Upon gradual increase of the throttle position sensor lever the RPM jump from 700 to 1050 as soon as the LGS - low idle switch shuts off (LGS inside of TPS is non adjustable). LGS turns on and off at approximately 13% of total range of TPS lever. Ater many hours of troubleshooting and replacing parts the problem has not been solved. I think that this might be inherent in its design and has become more noticable due to installation of a digital tachometer and changing propellers from 26 to 22 inch pitch (less load). In forward gear the jump is from 700 to 950RPM. Owners of this model engine could you please tell me if this is normal . Any responses would be greatly appreciated.
Bill D.

Bill,

Real difficult to trouble shoot over the internet, sounds like you have you been using Rinda tool? http://www.rinda.com/acro/merc_specs_v6.pdf trying to work on this motor without it is like being a one legged man at an ass kicking competition.

Saw you popped up with your answer after I had posted. I am afraid VM are a law unto themselves. As this is automotive base engine with Bosch EDC16? is SHOULD have for legal reasons an idle validation circuit. Nope I need to butt out I am out of my depth here.

Understand your dilemma, support for this motor in US sucks, others here have used independent VM dealers in UK with good results perhaps they can chime in.

 

[Parker]

Latestarter1
Thank you for your response. I may attempt to modify the wiper arms of the LGS- low idle switch inside the TPS. If I'm smart I'll give up and learn to accept this minor flaw. The engine runs great, although I have had some problems in the past. THANKS FOR ALL THE REPONSES Bill D.