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Under bonnet temp management

D

Dammit

+8cm
Joined
Nov 17, 2009
Location
London
I've just switched to a 90mm MAF housing for my 850R in order to accommodate greater than stock airflow with the 20T.

In heavy stop/start traffic on a busy day the engine cuts out - this is my theory as to why:

- The MAF, enlarged in order to accommodate the much higher than stock airflow is not great at low air flow any longer
- This is ok when temperatures are low to medium - when the car is in motion, basically
- In 10 miles of typical London traffic jam on a hot day the under bonnet temperatures climb significantly
- The hot, low speed air isn't within the MAF's ability to read
- It's the MAF sending "no air flow" to the ECU, which then cuts fuel, that is causing this problem

Sound plausible?

If so, what's the most effective way to manage very low speed/hot day/under bonnet temps?

Cut a big hole in the bonnet? Fit a massive fan?
 
do you get any codes check engine lights when this happens? If it is fuel related I would expect a code for bank too lean or maf sensor reading implausible too low or something like that.

but your car is old and stuff wears out. and if you dont get a code its probably your crank position sensor going bad. the signal from the cps will get weaker at low rpm and high temps. and if the signal stops the ecu will assume you stalled the engine and there will be no fault codes stored.

but if you still think its the maf swap back to stock and see if it fixes your problem.
 
If I had the original MAF that might be an option. You think it's unlikely though?

How would I check the cps- swap for a known good unit then see if it stalls?
 
The new housing was made specifically, and yes the car was remapped to accommodate the new intercooler, pipework, turbo and MAF housing.

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burstcurse said:
do you get any codes check engine lights when this happens? If it is fuel related I would expect a code for bank too lean or maf sensor reading implausible too low or something like that.

but your car is old and stuff wears out. and if you dont get a code its probably your crank position sensor going bad. the signal from the cps will get weaker at low rpm and high temps. and if the signal stops the ecu will assume you stalled the engine and there will be no fault codes stored.

but if you still think its the maf swap back to stock and see if it fixes your problem.
Click to expand...

Agreed. Just because it's hot and your not moving doesn't mean the turbo isn't sucking air past the maf still. It's unlikely a maf, start with simple solutions.
 
Quite easy on the 850s. Just on top of the bellhousing, centered between either side of the head. One bolt holds it in, 10mm socket.
 
cps is easy to check with an ohm meter over 1,000 ohms its done new they are around 500 ohms. they are easy to change and not to spendy. but when they die all the way the tow bill is about 4X the price.

so you dont have any codes or check engine lights?
 
Nope, no codes and no lights - fires back up as if nothing had happened, once things have cooled down a little.
 
I live in Arizona and summer temperature is in the 46C range. Never once my engine cut out in my 850 because of heat. The engine did cut out on my Turbo Dodge, but that's because there is a tear in the intank hose that leaks out fuel causing the engine to run lean under load.
 
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I intend on swapping the crank position sensor for a new one today- possibly a silly question but should I disconnect the battery before doing this, or just unplug it, pull old one out, new one in , plug it in again?
 
Hmm, 294 ohms between the pins of the sensor - that's within spec I believe?

Still likely to be the sensor, of something else?
 
I removed the old, and installed a brand new, crank position sensor today. I also swapped the coil for a new one.

I cleaned up the old CPS (it was oily) and dropped it in a mug of boiling water - 360 Ohms, which is still within the "it works" range.

How much hotter than ~90 degrees would the sensor get in stop/start, aircon on, hot day?

Or am I barking up the wrong tree on this and the sensor is fine - and what I need to focus on is finding the true culprit?
 
Also, fuel pump relay - could this be crapping out and generating my symptoms? Do they succumb to heat?
 
well get the laptop connected to it and log everything and make it do it so you can capture sensor inputs during the event. I still think that if it were the maf sensor you would see a code stored.
 
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