6 replies to this topic

[ajmount88]

Hi. I've been having idle quality issues with my mpi ever since I bought it 2 years ago. While things are now much better than back then (it does actually idle now), it's still a bit rough.

I have a s&p acr4 code reader that is showing MAP sensor readings around 50kpa at idle, which I believe is a bit on the high side a I understand things, so I was wondering I'd there was anyone out there in the Leamington/Warwick area that would be willing to lend me a known working MAP sensor just to check if it gives a different reading, so I know if it's the issue. I've already checked for air leaks and can't find anything, so I'm suspecting it's the sensor at fault.

Thanks

Alex

[Fast Ivan]

as you have the ACR4 you are in a position to test the MAP sensor without the hit and miss approach of swapping out sensors.

Does the MAP sensor reading change when you accelerate, i.e. does the value increase as the throttle opens?

 

As with most of the sensors you are looking at and checking that they operate when in use, so for example the CTS you should see rise steadily as the engine heats up.

[ajmount88]

Hi. Thanks for your reply. The MAP sensor values do change as the revs increase, so it is doing something. All other sensors seem to be giving sensible readings as well.

The reason I want to try another is that
despite there being no obvious air leaks the value is reading high, based on what I've read on here and from speaking to someone that used to be in engine calibration at Rover.

My understanding is that the idle MAP reading being high will either be down to an air leak, or the sensor not reading correctly. As I've checked for air leaks, I'd like to test the sensor. As a side note, the MAP does read atmospheric pressure correctly when the engine is off.

[tmsmini]

I am a few thousand miles away, so I cannot lend you an alternate sensor.

I can tell you that I have had the same condition through a few rebuilds and I have swapped sensors with no change.

 

My engine does have a few modifications Minisport modified head, ported inlet, lcb and whatever else they threw in.

 

When connected to the ACR I do see the change in vacuum, so although the reading may not be 100% accurate, it is relatively correct.

 

I would love to understand this as well. It has come up in a few other threads, so thank you for brings it to the top.

Terry

[Fast Ivan]

Hi. Thanks for your reply. The MAP sensor values do change as the revs increase, so it is doing something. All other sensors seem to be giving sensible readings as well.

The reason I want to try another is that
despite there being no obvious air leaks the value is reading high, based on what I've read on here and from speaking to someone that used to be in engine calibration at Rover.

My understanding is that the idle MAP reading being high will either be down to an air leak, or the sensor not reading correctly. As I've checked for air leaks, I'd like to test the sensor. As a side note, the MAP does read atmospheric pressure correctly when the engine is off.

 

Unless you're getting other driving symptoms/problems then I would say you don't have a problem, based on what you've said

[tmsmini]

Ran across this on the Blackbox Solutions web site that lists MEMS 2J info:

• Manifold Pressure (KPa): This displays the pressure measured by the external MEMS air pressure sensor. Normal reading with the engine not running is approximately 100 KPa and 30-40 KPa when the engine is idling. Very high values may indicate problems with the sensor or a blocked or disconnected vacuum pipe. Moderately raised values may indicate mechanical problems with the engine.

 

But as Fast Ivan said unless there is an issue, you don't have one. 120K miles in my MPi and on the third engine rebuild, all of them have had higher KPa.

 

This is where the MEMS Analyser that is available for the MEMS 1.6/1.9 would be nice to have for the MEMS 2J, as it allows for data logging.

 

http://www.rmrsoft.com/mems/http://www.rmrsoft.com/mems/

[ajmount88]

Hi again,

 

As I stated in the first post, I do have a rough idle though. It also also smells rather rich, and with the MOT coming up in less than a month, I'm looking to try to diagnose the issue and fix it, especially after it really struggled last year. Since the MAP sensor is an easy thing to swap out, and has readings that I suspect could be off, I wanted to try this to either confirm i have an issue with it so I can buy a replacement, or rule it out and look elsewhere.

 

Alex