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CO2 Emissions on 944

jellytott

jellytott

Member
Hi
Hi all in a nut shell I have a issue with idle hunting on a 944S 16v 2.5, its been a ongoing journey trying to resolve what generally plagues 944's with AFM and vacuum leaks etc yes, earth's leads, Ref and temperature sensors etc changed, so the car was left with a "respected Porsche specialist" they've resolved the huge flat spot between 2500 to 3200 revs but I'm stuck with idle hunting..... just out of curiosity what is the "ball park setting on idle on a 944S" as during a recent MOT the tester said on CO2 it was 1% for 944's with a limit upper 3.5% max for 1988 year, I.ve spotted it possibly set to 1.8% is this the case if anyone could confirm I would appreciate if I'm now chasing a problem that doesn't exist as mine set to 1% and is causing hunting on idle on cold start-up ?
Thanks
John
 
set to 1%?? I've not heard of 'setting' to a specific figure, I have always seen the Co2 reading as a guide to how well the engine is maintained, that is, how clean is the air filter and fuel system, both of which have an effect on the Co2 with hydrocarbons giving an idea as to how healthy the engine is. You are correct that your year car can go as high as 3.5%, for earlier cars this was 4.5%, IIRC my last MOT (951) showed mine at less than 0.5% but can't recall the exact figure.
Was the car hunting before going to the Porsche specialist (??) and what did they do to resolve the flat spot? these would be my first questions, your Co2 reading is fine.

Pete

 
Hi Pete
Originally, had inherent poor running with lean running, flat spot odd missing on acceleration off throttle and power back on this I acquired this when I got the 944S it was slowly getting worse.... I done the basics but was always left with this running issue..... so wanted it sorted so went to Porsche specialist they had it for 3 months changed:
  • ref sensor (but only) the main one had been wrongly installed and poor pickup.
  • additional hall effect by distributor ( something only on the 944S version I believe)
  • Temp Sensor
  • Adjust the AFM, spring tensions I think.

I'm left it with this "cold start hunting" after a few minutes running goes ? Garage suggests Voltage/earthing issue and perhaps too a tweaked Eprom ECU chip causing over fuelling on idle....I took the car back as I couldn't keep totting up an even bigger bill !!!! and even a longer time away with them.
I could trouble shoot these myself, so I'm after a Standard Porsche Eprom if and one appears from a S/H parts supplier, I really don't want to go on a bespoke Eprom just yet in case it masks a problem else where so hence going back to standard setup.

John

 
3 months and they hadn't fixed it?....wow, no wonder you took the car back. I'm not that clued up on the N/A's, whether 8 or 16 valves. You say you got the car like this and that it has a tweaked Eprom? I would agree with your approach in trying to source a standard chip and go from there. This chip could well be the issue, at least with a standard chip fitted you have a baseline to work from.
My one concern would be what did JMG do to remove the flat spot? Have they changed something mechanically or did they tweak the map on the aftermarket chip? If the latter then replacing the chip with a standard one should be straightfoward. If they've played around with something else then perhaps not.
Best bet is to find someone who has modified their S and still has the original chip. I still have my two original chips but they aren't suitable, or at least I don't think they are?

Pete
 
Hmmm.......Yes with the outcome to say the least I was expecting closure but unfortunately not !
The flat spot was resolved with sensor replacements and AFM adjustment, although they swapped the ECU and AFM from working spares it gave the same results and they never remapped the Eprom either.

So you can see why I posted here with the wealth of knowledge within the 944 forum as group here possibly someone may help/supply a standard Eprom or a ProMax chip just eliminate a unknown chip thats fitted in the ECU now. Thanks for the thought the 944S is a generic chip set for the S

Cheers

John


 
The ICV would be my starting point, they air leak around the junior timer plug and there is an O ring around the body to base joint that is possibly in three or four bits

a strip and clean and replace the O ring
 
I feared that you might say they played around with the AFM....ok if that's the problem and the last resort but since the issue is still there then clearly not and now that they have opened the AFM (I assume this is what they have done to modify the track?) then it makes it more difficult to sort with an original chip. I would still source a chip though and start again from there, Martin's suggestion is a good shout but I would have expected JMG to have looked at this part sooner than the AFM itself. In the old Day's Jon's place used to be very good, I recall attending one of his seminar's on how to do a belt change, this must be 20 years ago? However, in recent years I've not heard such good things about JMG, no experience myself but there seem to be some who feel let down badly.

Pete
 
”The ICV would be my starting point"
May I ask what the ICV is ? And also, is adjusting the spring tension in the Air Flow Meter an actual thing that should ever be done.
thank you Bremar
 
ICV

Idle Control Valve, and messing with the AFM is a very hit and miss affair, without knowing exactly what values should be at what point it’s impossible to get it right

 
Yes a possible with the ICV, I've done the basics already taken out and cleaned etc, I've used "Quick Start Spray" checking for vacuum leaks everything appears stable with revs don't vary with the quantity I've sprayed in the engine bay, again if the ICV doesn't modulate or wrong Eprom chip or now a wrongly adjusted AFM now.... yes I've been checking up on forums with ICV issues with taking apart and replacing the O ring and resealing the pins in the connector, I know it "clonks open and closed" but requires deeper tests apparently the ICV should modulate/vibrate feeling it with Ignition on and engine not running, also apparent the power output stage transistors fail in the ECU due to overheating on the pcb as they're lacking decent heatsinks they're easy to source and refit just know how to solder. Its just frustrating having to face these issues myself which I tried to get resolve by specialist....Nope!

I'll probably Post a request for a Standard Eprom (or ProMax) for a 944S, at least I can try it and also I have the capabilities to get copied and so cloned as a Original spare to fit in my ECU
 
When I ran a Rover SD1 single plenum Vitesse,it was generally very fast & reasonably economic-once I gained a lot more knowledge & importantly,confidence ,I started to tweak it a little at a time as I thought it idled too fast.
Armed with a newly bought exhaust gas tester ,good quality timing light with switchable strobe,combined with dwell meter & revcounter plus a separate engine multitester with revcounter,I started with idle speed & mixture adjustments,getting idle back down to the book 750 rpm IIRC from nearer 900rpm.
I then found the timing was well retarded & adjusted up to book figure which meant idle speed was again far too high-further wider reading suggested removing the vacuum advance pipe during adjustments which I did & advancing ignition by 2 deg was suggested as a tuning improvement.
End result was a stable correct idle.
Final initial tweek was to remove the AFM black plastic top & weaken the spring setting by 2 notches after which I had to generally repeat as above.
Car was immediately faster ,more economical with no flat spots,stuttering or fluctuating idle immediately returning to correct idle after thrashing it on motorways(the good old days )
So then,I fitted a fast road/rally Piper cam & lifters,Janspeed centre exhaust box with large backpipe and replaced the air intake system with that from a Jaguar XJ (deemed to have the much higher air throughput).
All above had to be repeated with the same result -the car regularly achieved 32/33 mpg fully laden inc windsurfing gear on roof rack
on high speed trips on motorways & would pull from low speeds to 90/95 without changing down from 5th gear.
The Rover had conventional distributor ignition with the Lucas /Bosch injection system as fitted to Porsches from the 944 /924S era & in fact our grey 924S has had the spring weaked by same amount with mixture adjusted appropriately giving a much better pickup with smooth idle.
I have always used Bosch Supafour spark plugs on all cars once they became available.
 
Thanks Vitesse pleased you've mastered tweaking up, love to have the kit and knowledge to do it myself but sadly let down relying on 3rd Parties to fix when I knew I couldn't
John
 
I seem to recall some young American chap on YouTube adjusting the tension on the basis the spring had probably lost tension over the years? And petrol explosive quality had also improved? or at least that’s how I remember it.
Surely the spring tension or it’s adjustment should be something to consider in tuning the 944 or at least there should be a way of testing to ensure that it’s set correctly. Does anyone know how to test for the correct spring setting. I’ve just taken the top off mine (the car works fine) just interested in the setting of this item. Thanks Bremar
 
The problem with the original AFM's is their age, they are pretty basic, a metal arm that swings on an arc over the graduated contact grid. This causes wear on the track and thus is where the problems arise. At the end of the day, the design is no better than the old Tamiya R/C speed controller 9for those who remember such things), very basic tech. It's the worn patches along the arc of the grid that upset smooth running and will give flat spots. Yes, you can try to get the arm to swing an arc on an unworn section of the grid but it's very much a hit-and-miss affair and will never be as it should. It does however help the car to run a little better if you do a good enough job.
 
HaHa Pete I was Scalextric lad...remember the brushes too !

Rumour's years ago that Porsche/bosch (like other NLA parts might remanufacture) plus a forum member might try for resistive pcb batch again ....so without that been looking for options seen Chinese pcb's for other AFM but the majority haven't got them to work at all, so with our 944 AFM's there's so many threads its a circle round and round never ending plus reading on the net this plagues our 944's them anyway plus add this appears to be a Black Magic thing to setup anyway!

Setup one post with setting up a AFM with the "spring defaults" are set by a calibrated weight on the barn door (with spring age would need adjusting) with a deflection defined angle reading and surely the track and wiper must be positioned at a start of the carbon track / to provide a known start point = voltage reference with deflection of barn door v quantity of air sucked in.

At some stage with time passing the only option with getting the stock AFM calibrated with no pcb parts available... logically the only option is a MAF/ECU replacement!
 
Well......Has anyone actually tried listening to the ICV valve with the Ignition on without the car running.
I was expecting it to buzz or vibrate felt with you fingers on the ICV body/top, I can't and the only way I can detect anything is a steel shaft on the ICV and pressing it on your front teeth even with that it's really really low level........ so is this normal or is this ICV buzzing a urban myth on the internet!




 
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