Hesitation at low RPMs

Ok yet another hesitation thread, I read completely no less than 15 threads including 328 and discarded the common issues:

Bad things:
1) when Cold, its very slow to start, cranks very fast (good battery, motor) but takes like 10-15 secs to start.
2) from 1000rpm to 3000rpm has som hestiation to accelerate

Good things:
1) when Warm, the engine starts in half a crankshaft turn, extremelly fast
2) after 3000rpm the engine pulls like there is no tomorrow
3) there is no fuell smell at any moment
4) idles very good, no vibrations and stable at 950-1050rpms

I started with the common isues with the FV... touching it I can feel it buzzing, so there is no need to check the FV Relay.... there is check valve before, I could remove it from the car and confirm if not clogged or something?

Also, the inyectors o-rings, I filled with fuell the small cavitity around them and started the engine, and the fuell was not drinked by the engine, so there is no air leaks there.

I checked all the hoses connecting the plenum, and all looks good at that end, I should trace it to the another end to confirm....

From my point of view it sounds like its lean for some reason...

any other idea?

 

Confirm that the water thermoswitch on the coolant expansion, item 77 here:

https://www.ferrariparts.co.uk/diagram/ferrari/32-mondial---cabriolet/023-cooling-system

is working correctly. It should be closed (i.e., resistance of only a few Ohms maximum between the two terminals) when cold -- this tells the injection ECU to add extra enrichment during cold-running via the FV and to ignore the (invalid when cold) O2 sensor signal (i.e., run open-loop). As a test, you can just connect the two wires going to the water thermoswitch together (simulating a cold, closed condition) and see if cold restart/cold-running behavior is improved, or not.

If no change = the next diagnostic step is to check the cold control pressure of the WUR as this (being correctly lower than during warm-running) is what also adds enrichment during cold-running.

 

ok, the water thermoswitch was a few Ohms so its "closed".

I went directly to the WUR, as it looks rusty, found it very complex... I tried to blow both fuel lines, and was almost closed, then I touched gently the
diaphragm from behind, and blowing looked less closed, but this is all sensations...

do you have a link or something to know how to test/confirm this was working? all inside looks pretty new (totally differnet as it looks outside).
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Chapter D of the Mondial8/QV WSM 281/83 -- link:

https://www.dropbox.com/s/z99soo68ny9n2qa/Mondial8qv_workshop_281-83.pdf?dl=0

You'll need the Bosch CIS Pressure Tester Kit (not necessarily identical to what's shown in the Mondial8/QV WSM, but readily available and not expensive). There should be videos on youtube as well.

However, the 3.2L in a US version 328/Mondial 3.2 (K-Jet with Lambda) uses a different WUR than those in the Mondial8/QV WSM (K-Jet without Lambda), and the cold and warm control pressure specs for it are here:

https://www.dropbox.com/s/e5pjuyiyo56vb13/328%20tech%20specs%20and%20service%20bulletins.pdf?dl=0

Would have been best to measure the cold and warm WUR pressures before disassembling the WUR to know if you've also changed the warm control pressure (which would require retweaking the mixture). I've attached a brief summary of how to tweak-up the US version K-Jet with Lambda system if you need it.

 

thanks, I will clean the WUR and then do a small drive test, I really want to do this a simple small step at a time... thanks for your time.

I have read all the time the K Jetronic is a very simple system, but just after disassembling the WUR I dont understand where the "simple" concept applies

2 diaphragms, 2 heaters, 2 levers, 1 spring, 1 aire connection... and how to modify/alter/reconfigure this?? thats not simple at all

even if I can confirm there is a pressure out of specs, I have no idea how to "reconfigure" the WUR to go in the rigth direciton....

 

small update... while the rebuild kit is coming, I decided to clean all, and just reuse the flapper but turned over.
that means, I put it upside down.

now a lot of black smoke, and no idle anymore

its incredible how a thin piece of metal can have such effect

just in the name of science, i will disassembly and assembly all back again as it was and confirm again

 

well car is working again, and idles stronger, I need to check how it goes with the hesitation issue.

the problem was the WUR was not correctly assembled.

 

This is the very cold AAV opening, its that ok? or it shoul open wider?
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I think that looks about right. These were used in other brands of cars at the time like Porsche, but is uniquely calibrated to the Ferrari. They open at different temperatures and different amounts depending on the application.

fyi, this is the place that can rebuild a core.

https://www.fuelinjectionproducts.com/en-ca/pages/about-us

 

An other idea:

Is yr cold starting valve working?
I have it disconnected because it leaks a bit
The car normally starts very fast
Yesterday when it was 0°C is started with great difficulty

 

ok, after
1) new sparks 2) new filters 3) new hoses, 4) check WUR, 5) check AAV and 6) plenum leak checks

I went to a full injectors-orings change... that was really easy after removing the lid...

this was a REAL change after all!!

now the car really start fast even on cold, and its more responsive on all rpms, but still no high idle... from cold it idles at about 900rpms

the next thing is to check 9th inyector the CSI... but for me, it looks rich already...

probably with years, the injectors started to underperform, and the mechanics increased full to compensate, now that the injectors are new, it looks rich.. but I will need more time to install a Wideband Landa with a clock and start looking how it runs.

 

ok the 9th injector was OK, good spry and no leaks when disconnected.

now measured control pressure and found things strange, with engine stopped the CP was 3BAR
Then after a few seconds went to 3.5BAR and after 4-5 mins stopped at 4BAR

is this OK?

I have many questions and options, because I feel it rich... should I modify the system control pressure to lower it? or that will make it even richer?

Or I should go directly ot the fuel distributor CO adjustemnt now?

(atm press is 1017 Hpa and Temp was 26 to 28 degrees)




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Can't recall anyone making this measurement and reporting the results. What does the regulated supply pressure do at engine shutoff? Does it show the same (increasing) behavior after initially dropping to the ~3 bar at shutoff?

 

It dos not increase passed 4bar... But did not drop fast either

 

So you are saying that the regulated supply pressure also immediately drops to the correct ~3 bar at fuel pump shutoff, but then slowly increases over a few minutes to ~4 bar?

(They should do the same thing as, after the plunger in the fuel pressure regulator closes, the control pressure volume and the regulated supply pressure volume are connected together by a small orifice so should be at the same pressure.)

Also, are you doing this test:

1) with a cold engine and just running the fuel pump electrically and then turning the fuel pump off, or

2) with a running warm engine (and a running fuel pump) and then turning the engine off?

 

1) this was 3 bar
2) this was at 4 bar, but after shutting off it dropped slowly to about 3.5-3 bar or so

Also, as said cold engine running it was 3.5 but increasing in mins to 4

I will replace the pressure regulator orings as all are 87' and retest ... What should be the next step? Going to the co mix and turn ir CCW or try to modify the shims in de PR to lower the pressures?

 

Confirmed twice:
1) engine cold starting 3b
2) engine cold running 3b-3.5b
3) engine warm running 4b
4) engine just stopped 3b
5) engine stopped 15min 2.8b

 

Those all seem OKish.

 

good, ok now I replaced both pressure regulator o-rings, and give no issues and no changes, (still starts in half a turn of the engine) I need to do a test drive.

next step will be going directly to the CO value... one thing in background, the car lived 37 years in USA, and now is in Uruguay so if it was on the rich side on the Oxigenated USA fuels, probably in our fuels its over-rich... so now that all was changed,tested, examinated... the final CO value is the only thing left....

as a resume:
0) basic service: fuel filter, air filter, oil filter, oil and gearbox oil.
1) 8 new injectors, with orings (this was a real change on starting the car, but the hesitation at 3k rpm was minimized but still there)
2) 9th injector tested, good spry, no leaks when off
3) AAV valve working good and tested
4) WUR working good and tested, all pressures validated
5) air leaks tested, a few hoses changed and all hoses tested, all ok
6) fuel pressure regulator orings changed (both, the front was looked smashed)

So I will start CCW the CO settings at 1/8 a turn at a time and check... if no luck with the "feeling" I will put a WideBand AFR monitor and see values, but no idea what could be a good target for this vehicle and have no much references on AFR scale... I think I saw som CO values and there is a relationship between CO and AFR...