Plumbing in vacuum / boost gauge

[gregp]

Hi all,


I'm wanting to install a vacuum and boost gauge to roughly act as a fuel economy gauge given the trip computer doesn't show instantaneous fuel economy very well.


I've plumbed the boost gauge into the map sensor line as per other posts (first photo below), but I'm only getting boost being read out, not vacuum. On the other hand when I connect into the wastegate line which was another idea (second photo), I get vacuum (inversely actually of what it should be, i.e. vac seems to increase with boost) but no boost!


This is my first diesel after years of petrol engines (including turbo) so please excuse my ignorance! I saw some 'diesel boost' gauges advertised which didn't show vacuum and have read diesel engines without a butterfly don't generate vacuum although the Pajero has a butterfly at the throttle body. Does the 4M41 generate manifold vacuum? I do really want to be able to see manifold vacuum as well as pressure if it all possible as that is part of the reason for getting the gauge.


Can someone help please? Is there somewhere else I need to plumb this in?


Thanks!
Greg

[nj swb]

Why not buy an OBDII reader of some kind? Scangauge / Ultragauge / bluetooth dongle with an app on a phone / tablet? Manifold vacuum is just one of the many parameters you can monitor if you so desire, like engine load (which is basically duty cycle of the injectors) and intake air temp. If you have an auto, you can also monitor your transmission temps.

Yes, the manifold does see small amounts of vacuum, but not often, and not much.

[old Jack]

X2 for OBD 2 monitoring of multiple engine and transmission parameters, you also get the added benefit of being able to read and clear fault codes.

OJ.

[gregp]

thanks for the suggestions guys I was really just looking for a simple gauge that I could glance down and check how the readings were going rather than a more complicated computer display that you have to scroll through and press buttons and things. But maybe I'll check it out if that's the best option.

[old Jack]

thanks for the suggestions guys I was really just looking for a simple gauge that I could glance down and check how the readings were going rather than a more complicated computer display that you have to scroll through and press buttons and things. But maybe I'll check it out if that's the best option.

Ultraguage will display up to 6 parameters at any one time with the ability to set alarms.
Scanguage will display 4 parameters, no alarms and poor daylight contrast.
Torque Pro uses you smartphone and can display multiple parameters.

I have a Scangauge because 7 years ago it was the only one reading ATF temps, times have moved on and if I was to purchase now then an Ultragauge MX1.3 would be my choice.

OJ.

[nj swb]

thanks for the suggestions guys I was really just looking for a simple gauge that I could glance down and check how the readings were going rather than a more complicated computer display that you have to scroll through and press buttons and things. But maybe I'll check it out if that's the best option.

I run Torque Pro, which is very flexible, and can display configurable gauges - good for that quick glance:

[Skinny03]

Hi Gregp,

I don't think you will get a diesel to post a negative (vacuum) intake manifold pressure like a petrol engine hence why they run a vacuum pump for the turbo actuator (wastegate or VGT), brake booster, front diff actuator etc, but I may be corrected here. Every light diesel I owned has run a vacuum pump. You may get a instantaneous negative reading under certain "off the throttle" situation but nothing substantial for what your after. The butterfly valve in the intake system on the 4m41 , "I think", is to assist shutdown.

[_jp_]

Hi Gregp,

I don't think you will get a diesel to post a negative (vacuum) intake manifold pressure like a petrol engine hence why they run a vacuum pump for the turbo actuator (wastegate or VGT), brake booster, front diff actuator etc, but I may be corrected here. Every light diesel I owned has run a vacuum pump. You may get a instantaneous negative reading under certain "off the throttle" situation but nothing substantial for what your after. The butterfly valve in the intake system on the 4m41 , "I think", is to assist shutdown.

I'm of the same understanding.

[gregp]

Thanks for your help guys. I'm trying to do this on a budget so got the EDS tool. Hopefully this does what I need? I've also been told exhaust gas temperature is important to keep an eye on when towing, but it doesn't look like EDS or Scangauge does this. I guess the ECU has to be able to monitor something for it to show up in OBD2 and I assume the exhaust probe is just for air:fuel ratio, not exhaust temperature.


I hope I haven't bought a dud product i.e. one that doesn't monitor boost OR EGT!



Thanks,
Greg

[carnut1100]

EGT isn’t a sensor that OBD has, so you can’t monitor it with a gauge.
You will need to fit a gauge.
Fit it upstream of the turbo if possible, and downstream of where the manifold branches merge. You want exhaust from all cylinders before it has cooled a couple of hundred degrees through the turbo.

As for boost, I like a dedicated gauge too, but Torque Pro does a very good job for about 5 bucks and another tenner for an ELM27 Bluetooth OBD dongle. Cheap dongle might not read codes properly, or it might...people’s experiences vary, but 5 bucks is a cheap gamble.

You do see vacuum occasionally, but not much and I wouldn’t buy the gauge with that in mind.

I always drill and tap the intake manifold directly for boost gauges.

[Mike DiD]

Is a Vacuum Gauge any use to show Fuel Consumption Rate in a Diesel ?

[Muzza]

Is a Vacuum Gauge any use to show Fuel Consumption Rate in a Diesel ?

No, neither is a boost gauge if the vehicle has a VGT turbo, a EGT gauge would be a gauge that could be used to assist in driving to improve economy.