400i idle adjustment

Peter,

When I got my 84 400i, I adjusted exactly as the manual says using a vacuum gauge. It is a bit of back and forth between bank synchronization and fuel mixture, but I had the car balanced and passing smog in about an hour.

I have an inexpensive Gunsen CO Tester which has come in very handy over the years

Tony

 

Just resurrecting this thread for a clarification...........
Just took my car on the road today for the first time after a three year restoration which included a full overhaul of the fuel system, and trying to get it onto shape for an emissions test next week.
I'm looking at the Ferrari Injection Manual (print version shown as cat. 178/79 n 700 on the back cover), and specifically at Fig 60 "Engine rows synchronisation". Am I correct is assuming that this diagram shows the use of two (presumably) mercury manometers, each of these being teed in to the vacuum line between intake manifold and WUR? (I'm intending to use bourdon type vacuum gauges)
And presumably the objective is to achieve similar vacuum levels on each bank, which would (or should?) imply similar airflows at idle speed to each bank?
Secondly, the manual makes no reference to disconnecting the throttle linkage so that each bank can be adjusted independently of the other, but it seems to me that this must be done first, as the OP states above. Am I correct?
And finally, I find that an idle speed that is significantly above 900 rev/min results in an unpleasant "clunk" when selecting gear (automatic transmission). Does anyone have any comments on this, or indeed any information to indicate that achieving minimum CO levels is affected by the idle speed?
Pat

 

.....and another question!
Am I correct in thinking that the WUR in the idle position (and after the bimetal strip has fully heated) has no influence on the idle mixture? The reason for asking is that, as I understand it, the two WURs are cross-linked together with a balancing pipe which balances the control pressures between the two banks in the full load condition. At idle however, each WUR has a vacuum line to it's respective inlet manifold, and this vacuum will vary depending on the butterfly adjusting screw setting- thereby changing the control pressure on both banks.
So the question is- should one blank off the cross-linking/balancing pipe between the two WURs while setting the idle speed?

 

The manual is poorly written and the factory gave us very different adjusting procedure which aligns far better with other models and makes.

Other than being sure the WURs are in spec and connected properly forget about them. Disconnecting interconnecting linkage for tuning is boiler plate.

Close bypass screws completely. Set idle with stop screws to 750 with mixtures to about 1.5 % letting CO2 numbers be your guide. Set idle to spec using by pass screws resetting mixture as before. Adjust as required linkage and reconnect.

 

Just to add some more detail to Brian's post, at both the 750 RPM idle speed (air bypass screws fully closed), and the final warm idle speed setting (air bypass screws open some), the vacuum level in each intake plenum should be the same.

 

Thanks to both for the inputs.
Before I saw your posts, I tried to follow the WSM procedure keeping both bypass screws closed. I managed to get a nice smooth idle at around 750 RPM (both bypass screws closed) with CO levels around 1.2% and HC reading around 600ppm. Both banks giving the same readings plus or minus 10%. Then I tried to increase the idle speed to the spec setting of 900-1100 RPM using the butterfly stop setting, as seems to be suggested in the WSM, and still not touching the bypass screws, but the CO levels shot up. Leaning out the mixture screw didn't help, (Still not touching the bypass screws), CO did come down to around 2% but idle speed dropped and idle became rough. At that point I ran out of expletives and left the thing until I get my vacuum gauges and fittings lined up.
I can see that your recommended procedure using the bypass screws to adjust the final speed is more likely to work and wouldn't result in the rich mixture which stymied me today.

 

Messing with the WURs is not always a good idea, but I would still check they are "within spec". It's a good idea to separate the interlinkage between the two Wurs and check cold and hot pressure (on both banks). If the two set of pressures are correct you can indeed re-install the balancing hose and just forget about the WURs.

In order to test the pressure, you need the proper vacuum gauges ($80 on ebay), these are sold with the short Banjo bolt which allows to temporarily get rid of the interlinkage.​

I also usually disconnect the cold-start injector when adjusting the CO. This way I know I am adjusting the CO regardless of any "external" enrichment. My (new & ridiculously expensive) thermo time switch (which drives the cold start injector) kicks in from time to time which can make the adjustment frustrating!

 

K Jetronic or CIS, whichever name you prefer is not the best fuel injection known to man but its what we have and does work pretty well. At low RPM mixture changes quite a bit with idle speed adjustments. Its why it needs to be adjusted when idle speeds are changed.

600 PPM is too high. If the engine is in otherwise good tune and condition I would expect more like 300 or less. Preferably less that 200. One thing that can explain that and possible other issues too is the ignition timing. The engine has 2 very common reasons for idle issues with excessive HC . The distributor drive is pretty well known to slip and stick in the wrong place. It uses a rubber o ring to control end float of the drive shaft and it is driven by a helical gear. O ring gets old and it quits doing its job. Really dumb design. Also the distributor internally has the worlds most ignored advance mechanism. Between the plastic bushings that with age swell and sieze and lack of lubrication it is unusual to see one working correctly. Another explanation for high HC is cam timing. The 400 has the longest drive chain in any Ferrari motor. They stretch a lot and are scheduled for routine replacement every 25000 miles. That is over and above the pretty common cam timing maladjustment from poor servicing in 4 cam motors.

 

If you have any doubt of proper operation of the cold start system fix it first. Its a very simple system and will interfere with anything else you are doing. Disconnecting it is just not the way to go about it.

 

It's a Ferrari...

(I did replace the thermo time switch, the relays and the cold start injectors "just in case" but still do not trust this "electrically operated" portion of the k-jet)

 

In my experience they are pretty reliable.