Resurrection of my CQ20V

[Bowie69]

The cross sectional area of the 7A MAF is smaller than the throttle body.... I'm sure of it.

[steve briance]

I think youve just explained what i thought but couldnt really put into words!

On a Normally aspirated engine, i can't see a big MAF feeding a smaller inlet tract making any benefit. Like you, I've also resigned myself to making mine the best it can be using original stuff apart from the injectors which were as much an available fix for unavailable failing orginal items.

[Obli]

For gas and fluids, if you increase the cross-sectional area (i.e. bigger pipe) the velocity will slow. If the volumetric flow rate is lower with the V6 MAF then it doesn't matter how much bigger it is. Or am I oversimplifying it all?

I wonder these days whether just to keep it all original and concentrate on getting the car running healthily, as it was designed, and enjoy it for what it is. I've so often fallen into the trap of thinking I might know better than the design engineers, surely they've overlooked this and that. I don't know better. Still, it's fun trying to improve things and makes for good discussion but in my experience there's always a trade off and usually I just end up making things worse

[Bowie69]

Sounds like MS is the answer then....

I've used it a fair bit before, just mostly Rover or Lexus V8s, I think I can use the dizzy pick up quite easily, so that should be OK, if I remember right...

[steve briance]

The mapping process showed there was nothing wrong with the amount of air the engine was getting, unfortunately the map for wide open throttle seemed to be stuck in a part of the map which could not be accessed. Shame really as it just wasn't possible to enrichen for best fuel air ratio for power. There would have been no benefit to getting more air in there

[Bowie69]

I'm not sure about what you Automark was saying, the 7A MAF is tiny, a real restriction, it won't slow the air flow by going bigger apart, but in the MAF itself it will speed up of course, which is no good thing, it is just indicating a restriction.... If you can get a reading to the ECU which make some sense, then I would suspect it would be fine.

Yep, MS is job for another day, I think even the triggering is not quite as simple as it should be, being 5 cylinder.

[steve briance]

V6 maf? Been there and tried that as well!

I went to see Automark for some remapping work as far as was possible with the 'difficult' bosch ecu it had and before starting, i discussed fitting the v6 maf and mapping for that... He raised an interesting point that it would most likely slow down air velocity as the 2309cc has a fixed ability to suck and making that fixed ability to suck, suck through a bigger hole would result in maybe sucking easier but definitely slower.
Analogy - use your lungs to blow througg a drinking straw then a drain pipe. Same amount of air moving but comes out of the straw as a flow but its easier through the bigger pipe.

I stuck with 7a maf and housing as the last thing a 20v needs is for the airflow to slow down as its why it doesn't really build torque until higher rpm when air starts to have its own momentum. The wonderful inlet manifold was part of the effort to improve abd and make the best all rounder for the job.

Having said all that, i do often wonder what a 7a would be like on a standalone ecu... I suspect it would make more of everything

[Bowie69]

To be honest, I'm more tempted to go the route of the V6 MAF and related jiggery pokery with resistors and the like, and then I assume it won't work quite right and I will bin the lot and Megasquirt it

[steve briance]

Been there done that with bosch injectors and also concluded they run rich. On my ua they seemed to be the cause of iffy cold idle (the infamous bouncing 7a idle) and a hesitancy on part throttle before its done 2 or 3 miles. My fix?...
An adjustable fuel pressure regulator.

The flow figures quoted for bosch injectors are at 3 Bar and the 7a fpr is 4 Bar. Makes quite a difference so to get anywheeeclose to the original Hitachi flow rates, you need to turn down the pressure. When i say hitachi flow rates, its not easily found but i saw figures around 260-270cc/min. It wasnt clesr if this was 3 or 4 bar but being as they were designed for a 4 bar system, you have to conclude it was a figure quoted at 4 bar.
315cc min bosch reds at 3 bar becomes something like 360cc min at 4 bar.

Its not hard to see how much extra fuel the lambda and maf are trying to deal with.

Fitting an fpr involved custom made bracket for me and some combination of adapters depending on the thread your new fpr comes with...

It may sound counter intuitive reducing the fuelling from the bosch reda which come with a reputation for 'sorting out the fuelling' but to be honest, they are too much and i feel the ecu is always having to trim it back. Mine drives and behaves much nicer now ive trimmed it back with the fpr.

Good luck

[Bowie69]

That can happen, large seals that fail, but if not leaking and left alone, probably fine.

[John.]

Always thought the injectors were a must have upgrade.

I changed mine as I'd read somewhere that they were a fire hazard ?....... something to do with them cracking/breaking perhaps?

[Obli]

Thank you Sir.

Always thought the injectors were a must have upgrade. Did you notice a performance improvement over the Hitachis?

I should be able to rule out lambda probe, coolant temp sensor, MFTS, spark plugs, fuel pump as they were done 2,000 miles ago. I'll definitely check the CO.

It's not a crippling limp mode. Engine idles smooth hot or cold, doesn't stall and picks up cleanly, but mid to full throttle around 3.5k+, I get a fluttery hesitation. It's not violent. It's like a switch flicking between 80% and 100% power during acceleration. Driving more gentle, one may not even notice it.

I really need to get around to working out the blink code tester.

Sorry for jumping your thread!

[Bowie69]

Yes, knock sensor part number difference is just cable length, otherwise I can't see any physical differences.

I am running bosch red injectors with adapters now, honestly they are a bit rich, though I think my MAF also may be playing up a bit, so basically it all needs a going through when I get time. I used to run some Volvo injectors, which were fine, again a bit rich, but I was conscious that even those were getting on a bit I splurged on new bosch reds.

If your hitachi are working, i would honestly leave them.

The hesitancy at 3.5K I have had, I think mostly it comes from the engine going into limp when in warm up, so check temp sender, MAF readings with something like OBDEleven.

I think I found a cut to length silicone hose for the thermostat, honestly can't remember! I'd like Ultraperformamce to make a stainless pipe for there, but only do a turbo variant at the moment.

[Obli]

Interesting. If I manage to improve/eliminate the drone on mine, I'll post up what I did. I've got a Helmholtz resonator designed which I'm fairly confident about. It's going to attenuate (reduce) the low frequencies (booming) generated around 2,200rpm +/- 400rpm. The only unknown variable in the formula is the exhaust gas temp before entering a custom centre box. Obviously going to fluctuate but need a fairly decent idea when engine is warm and driven at cruising speeds. I've been guessing about 175 deg C (350 deg F) for now. I think I'll uncouple the exhaust and get a measurement on it and then rerun my calculations. Then I can order the materials, fabricate and fit

My 90 20v (early engine, 2 plug ECU, bag-o-snakes etc.) has developed a hesitancy around 3.5k+. Started doing it a couple of days ago. I'm going to replace the knock sensors as they're 32 years old and the most likely culprits. Thanks for the earlier info in this thread on the two Bosch knock sensors, very useful. Are the blue and green variants simply cable length differences, do you know? Has your car been running OK using the doughnut design? I've noticed the aforementioned Bosch part numbers cross reference the Audi part numbers for the 10v engine knock sensors, so forgive me but I was slightly skeptical. I wondered why the 7A knock sensor p/n would be unique, unless it's simply a cable length difference?

My issue could also be the old Hitachi injectors. Are you running the orange/red Bosch injectors? If so, how have they been? I've been looking for a good excuse to do mine but historically I've had no issues with the Hitachis in 209,000 miles so couldn't justify binning them while working.

I like the look of the Ultra Performance stainless coolant stub from the thermostat housing. Might have to acquire one of those Would like to replace the long, straight hose too. Did you use a generic silicone straight hose cut to length?
No further questions, your honour!

Cheers,

James

[Bowie69]

It is custom stainless and 2-2.5K is worst for sure.