AJP8 4.5 tuning after rebuild
Discussion
Hi
Right so I've got this project where I've been rebuilding a 4.5 cerb, I got it in the state where the main block had been sent off for a proper internals rebuild and needed all of the rest of the systems fitting and setting up. As a result the idle screws and everything have lost their settings so i'm starting from scratch.
I understand that the engine MBE ECU uses the RPM and the TPS sensors to pick a fueling amount and then makes adjustments to this amount for each bank AKA adaptives.
I tried to get the engine idling properly with some aftermarket blue TPS Potentiometer sensors but it was: A idling too high and B: spitting and popping a bit.
I've used the RSiAJP app to set it up and record data. The data showed that one of the TPS pots was spiking readings.
I've now replaced them both with a fancy set of hall sensors and the readings of position are much more stable. My question to the community is: how high have you all had to set your TPS sensors at idle in percent? I read somewhere that it needs to be around 16-17% but mine wont start or idle at that.
My method was this:
- set the butterflies as closed as they can go separately.
- join the linkage bar and tweak its length whilst listening to when they sound like they are both closing at the same time
- get some pretty strong springs to hold the linkage properly closed so theres no variation or float to the idle position
- set TPS sensors to 16-17% ish
- hit start button
- wont start
- open throttle slightly by hand and hit start
- engine starts
- engine dies as soon as i let go of throttle cable to open throttles.
- raised idle screw to increase idle speed air flow
- set TPS sensors back to 16-17% at new position
- hit start
- engine idles and starts but its too high, like 2000rpm
note adaptives are adding around 20-30% where one bank is higher like say 22 one side and 30 on the other side
- I decided that this was saying that the mix is lean and considering it was idling too high i did the following:
- adjusted idle screw position to reduce air flow from butterflies
- reset TPS sensors higher to about 30% at idle
- checked full swing on throttle linkage, maximum got to 94% so feels like im good as i've still got resolution at high throttle openings
- got told off by neighbour for making too much noise.... cancelled session!
so this is where I am at... has anyone else had to set their TPS sensors around 30% ish to get it to idle?? If its obscenely high I might have an air leak between the throttle bodies and the cylinder heads - the orings were a pain to install without dropping so I wouldnt be surprised if one of the 8 was slightly unseated. I dont want to take it all apart for nothing though. thoughts?
Right so I've got this project where I've been rebuilding a 4.5 cerb, I got it in the state where the main block had been sent off for a proper internals rebuild and needed all of the rest of the systems fitting and setting up. As a result the idle screws and everything have lost their settings so i'm starting from scratch.
I understand that the engine MBE ECU uses the RPM and the TPS sensors to pick a fueling amount and then makes adjustments to this amount for each bank AKA adaptives.
I tried to get the engine idling properly with some aftermarket blue TPS Potentiometer sensors but it was: A idling too high and B: spitting and popping a bit.
I've used the RSiAJP app to set it up and record data. The data showed that one of the TPS pots was spiking readings.
I've now replaced them both with a fancy set of hall sensors and the readings of position are much more stable. My question to the community is: how high have you all had to set your TPS sensors at idle in percent? I read somewhere that it needs to be around 16-17% but mine wont start or idle at that.
My method was this:
- set the butterflies as closed as they can go separately.
- join the linkage bar and tweak its length whilst listening to when they sound like they are both closing at the same time
- get some pretty strong springs to hold the linkage properly closed so theres no variation or float to the idle position
- set TPS sensors to 16-17% ish
- hit start button
- wont start
- open throttle slightly by hand and hit start
- engine starts
- engine dies as soon as i let go of throttle cable to open throttles.
- raised idle screw to increase idle speed air flow
- set TPS sensors back to 16-17% at new position
- hit start
- engine idles and starts but its too high, like 2000rpm
note adaptives are adding around 20-30% where one bank is higher like say 22 one side and 30 on the other side
- I decided that this was saying that the mix is lean and considering it was idling too high i did the following:
- adjusted idle screw position to reduce air flow from butterflies
- reset TPS sensors higher to about 30% at idle
- checked full swing on throttle linkage, maximum got to 94% so feels like im good as i've still got resolution at high throttle openings
- got told off by neighbour for making too much noise.... cancelled session!
so this is where I am at... has anyone else had to set their TPS sensors around 30% ish to get it to idle?? If its obscenely high I might have an air leak between the throttle bodies and the cylinder heads - the orings were a pain to install without dropping so I wouldnt be surprised if one of the 8 was slightly unseated. I dont want to take it all apart for nothing though. thoughts?
The 20 odd years ago advice from Joolz was:
If the banks are balanced, then the adaptives should be equal. It really is that easy.
The garage should have an airmass meter ... it comes supplied in the cerbera kit that every dealer got along with their computer / software / cam timing gear. I very rarely use the meter and just balance it from the values on the screen which is much quicker, but if you had a SP6 then I'd be worrying...that engine has individually adjustable butterflies for each cylinder and you cannot balance this without the meter.
The basis for setting the V8 is to firstly slacken the linkrod between the banks, then by interpreting the adaptive value relative to the throttle pot value bank to bank you can deduce which bank is sucking more air (assuming equal t-pot values this is the bank with the higher adaptive value) there is no other way of interpreting the values .. it's as simple as that. You just adjust the link / throttle pots and idle screw to get the adaptives equal, but also AS CLOSE TO ZERO AS POSSIBLE! If one bank of your engine has adaptives of around 30 % then this is running about on the rich limit ... it won't enrich any more than that. So this means your engine needs a good tune up.
It's also wrong to say that the ECU throws up spurious fault codes in the garage such as the AFR error ... there's a logged fault because there IS a fault ... it's the difference in airflow that's causing it. The imbalance is more noticeable at small throttles / lightcruise conditions and getting it right can give much better town driving.
If the banks are balanced, then the adaptives should be equal. It really is that easy.
The garage should have an airmass meter ... it comes supplied in the cerbera kit that every dealer got along with their computer / software / cam timing gear. I very rarely use the meter and just balance it from the values on the screen which is much quicker, but if you had a SP6 then I'd be worrying...that engine has individually adjustable butterflies for each cylinder and you cannot balance this without the meter.
The basis for setting the V8 is to firstly slacken the linkrod between the banks, then by interpreting the adaptive value relative to the throttle pot value bank to bank you can deduce which bank is sucking more air (assuming equal t-pot values this is the bank with the higher adaptive value) there is no other way of interpreting the values .. it's as simple as that. You just adjust the link / throttle pots and idle screw to get the adaptives equal, but also AS CLOSE TO ZERO AS POSSIBLE! If one bank of your engine has adaptives of around 30 % then this is running about on the rich limit ... it won't enrich any more than that. So this means your engine needs a good tune up.
It's also wrong to say that the ECU throws up spurious fault codes in the garage such as the AFR error ... there's a logged fault because there IS a fault ... it's the difference in airflow that's causing it. The imbalance is more noticeable at small throttles / lightcruise conditions and getting it right can give much better town driving.
thanks yeah i think i need to interrogate the air flow - it must be higher than needed which is making the idle fuel mixture lean. Probably a leak... however I just thought i'd ask to see if there are any subjects I've missed... any other ideas out there?
I've got the brake boost hose connected.
i've got the air line that goes to the carbon cannister and throttle bodies open (i did have it blocked, made no difference)
I've got the brake boost hose connected.
i've got the air line that goes to the carbon cannister and throttle bodies open (i did have it blocked, made no difference)
Edited by Krog 4.5 on Tuesday 14th July 14:49
As a starting point - disconnect the link rod and wind the idle screw all the way out. Make sure the butterfly's are fully closed & set the TP's to 15%. Then reconnect the link rod and adjust it until the TP's still both read 15%. If it's too long or too short one of the readings will be off. When the link rod's connected and both TPs read 15%, wind the idle screw in until they read 19%. This is a good starting point. It doesn't mean the engine will be in balance, but you should only have to make small adjustments from this position.
I posted an alternative method for balancing the AJP here:-
https://www.pistonheads.com/gassing/topic.asp?h=0&...
There's a link to a video near the end of the 2nd page. It might help.
I posted an alternative method for balancing the AJP here:-
https://www.pistonheads.com/gassing/topic.asp?h=0&...
There's a link to a video near the end of the 2nd page. It might help.
this is great thanks for sharing.
The step where you use the idle screw to set the butterflies open a little AFTER setting the TPS at 15% is absolutely a step I havent tried... I shall do that next.
Great video
So if the adaptives are saying 30% positive at this starting point then its saying my engines running very lean and so it'd be likely to have an air leak somewhere thats dragging in more air than intended which is ruining the AFR
The step where you use the idle screw to set the butterflies open a little AFTER setting the TPS at 15% is absolutely a step I havent tried... I shall do that next.
Great video
So if the adaptives are saying 30% positive at this starting point then its saying my engines running very lean and so it'd be likely to have an air leak somewhere thats dragging in more air than intended which is ruining the AFR
Edited by Krog 4.5 on Tuesday 14th July 16:36
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