348 - Engine repair thread | Page 19 | FerrariChat

348 Engine repair thread

Discussion in '348/355' started by Ferrarium, Oct 13, 2021.

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  1. Ferrarium

    Ferrarium F1 Veteran
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    Right, but understand the screw behavior. You can do it with the car off, then put it back to the number before you messed with it. t's not as clean as turn left numbers go down guaranteed. It's why people say they turn it and see no difference. I can turn is 1/4 turn and see 0 difference. infavt the.resistance does not change. Other times touch it a hair and numbers jump.
    Not as clear cut as left down right up like clock work with same increment turns.

    There is a technique is all I'm saying.

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  2. KevZep

    KevZep Formula Junior

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    Yes I know about that, I have had my multimeter on mine and stupidly adjusted them to 383 to find it was worse and also found they didn't want to be the same to be even if you get what I mean, but I don't want to make any more adjustments until I have the wideband O2 sensor on it and do a few runs on the dyno, I am hoping I can do this on Saturday.
     
  3. m.stojanovic

    m.stojanovic F1 Rookie
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    This picture shows the internal potentiometer (blue rectangle) and the "S" coupling connecting the pot's spindle to the adjuster screw. There is quite a bit of slack in the coupling so, when you change the direction of rotation, you first go over the slack (nothing happens) then the pot starts turning. The pot itself (second pic) also has some internal slack which adds to the overall "gap" in the response of the potentiometer.
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  4. m.stojanovic

    m.stojanovic F1 Rookie
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    This diagram is from the 348 manual. It can be seen that only two "legs" of the pot are used (one fixed side and the wiper) so it actually functions as a simple variable resistor, not really as a potentiometer. The fixed side of the pot is connected to the ground via MAF's pin #1 and the wiper internally connects only to the free pin #6 meaning the pot does not form any part of the MAF's circuitry (does not alter the MAF's signal) but connects to the pin #43 of the ECU. MAF's pin #3 is the signal representing the air mass; pin #4 ("burn") is for the brief voltage supply coming from the ECU at engine switch off to burn-off any contaminants on the MAF's hot wire.
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  5. Ferrarium

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    I was wondering what caused that slack, its excessive when changing direction. makes sense, thankyou. As I mentioned people try and measure it with the maf plugged in, make changes and say nothing happens.

    Best to go back then forward once you see changes with meter then go in one direction only. If you have to go backward it's tricky without measuring when the slack is taken up given that it takes a few minutes for gases to calm after a change. Also best to blip the throttle and let it settle.

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  6. m.stojanovic

    m.stojanovic F1 Rookie
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    I once tried to measure the pot resistance while the MAF was connected. The resistance readings were very different because the pot (resistor) is in this case part of the ECU's circuitry so the multimeter also picks up some other parallel resistances along certain paths in the ECU's electronics. This is my "MAF Connector Interface" (I marked it "+ rich", "+" meaning higher Ohms, because I always forget which way is richer and which leaner).

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    I made the male side by cutting it out of a bad Volvo MAF. Otherwise, these 6-pin male connectors are a bit difficult to find. I only found this Australian supplier to have both, male and female kits:
    https://www.efihardware.com/products/2830/Bosch-6-Pin-Male-Timer-Junior-Connector
    https://www.efihardware.com/products/1597/6-pin-igniter-plug-kit
     
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  7. KevZep

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    Typical multi-turn trimmer behavior which will catch people out who are not familiar with this sort of thing.
    My current job involves audio based electronics where I am adjusting a lot of these type of components for various adjustments.
    Its going to be interesting armed with a bit more knowledge of the operation of this system to see if we can get things more on point.
    My car seems okay but it could definitely be better...
     
  8. Ferrarium

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    Just remember it's open loop trim not closed. Let us know how it goes! Take pics!

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  9. Ferrarium

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    #459 Ferrarium, Dec 23, 2022
    Last edited: Dec 23, 2022
    I balanced the throttles between banks today. You can do it with power applied and car not running it you use the harness type I employed. Difference between banks throttle position:
    Idle - 4mv
    20% - 3mv
    40% - 0mv
    60%- 30mv
    90%- 10mv

    To be fair I did not have to adjust anything it was dead nuts presumably because I set the TB's at .05 mm gap and set the TPS as exact as I could get prior. Your allowed 80mv difference I had 4mv difference at idle position. For the throttle open positions your allowed up to 100mv difference.

    How about those shiny brand new OEM TPS sensors and MAF's. :)
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    Here is the manual details for others who need it, the forum is shrinking the image.
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  10. Ferrarium

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  11. KevZep

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    Looking great!!

    Showroom condition!!

    I like your harnesses there, makes things a lot easier....
     
  12. Ferrarium

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    I have the 2 factory ECU pinout boxes too, but the harness is just much easier.
     
  13. KevZep

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    Your last few posts have inspired me to go right through the throttle setup and revise everything I can whilst I wait to get on the dyno. As I mentioned I did get mine idling quite well but I feel it could be better, and armed with a but more knowledge and tracking your progress, I should be able to get things better than they are.
    My car actually idles at 1050rpm which is messing with my OCD!!
    Its early here so I'll have to wait for a few hours before I wake up the neighbors...lol.

    This is one of the best threads we have for setting up our 348's!!
     
  14. Ferrarium

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    Yeah if the tb gap is not right getting the air screws right for idle is really tough. I started with the max clearance of .05 mm but I can always go down if needed. Use 2 feelers one on each side.

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  15. Ferrarium

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    #465 Ferrarium, Dec 30, 2022
    Last edited: Dec 30, 2022
    Just heard back from my friend with the SS he's owned for 20 years, the MAF's were set at the factory to:
    • 379.5 drivers side and
    • 384.1 the passenger side

    Ok back to me....

    It was still gurgling and surging and it seemed to coincide with the air injection coming on, although it never came on because it would bog so never really heard it. Everything is new so it has to be something simple. It also idles fine when warm. I sprayed starter fluid everywhere when cold, no leaks...

    Went over vacuum hoses for the injection seemed fine. Looked up some pics I took. Turns out the depression tank has a check valve in it. The manifold vacuum hose I'm pointing to was plugged into the wrong port according to my pre dis-assembly pictures. So I swapped those 2 hoses. Fired it up, idled great and air injection came on with the familiar growl and no bog or surge. Air injection went off and it idled fine. I assumed it was just an empty basin so I did not mark which hose was for what. There is only 2 of them and 3 ports. I assumed it made no difference. It does..

    Found 2 coolant hose leaks where the band clamps were not quite tight enough, quick 1/4 turn and that solved that. I set the MAF's to 378 for now. Will measure voltage etc at a later time.

    Bled the cooling system again, fans come on at 190 on the button, prior it was a bit over that with the air in the system. Will likely bleed again it every time I start it for a few times.

    Set the banks vacuum the same, idles a bit high so I may redo the TB's down to .03mm air screws are 1/2 turn out. Boy it sounds good though, deep and smooth.

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  16. KevZep

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    Remember right at the beginning of the hullabaloo I thought it was vacuum related, but what a journey its taken you on, you've even taken me on a journey with my car which has worked out well in the end.
    Good to do a bit of checking to solve those little leaks and so forth, looks like you're set now.

    Must feel good to figure it out though, I suppose the weather is preventing you from taking it out for a blast!!
     
  17. Ferrarium

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    Yep few folks said vacum, issue is there was no leak so I could not figure it out. The injection not coming on and surging when it was supposed to, you could hear the solenoids so it was related to that which led to check and compare lines to prior pics. Prob won't t take it put till spring as I still have to button it up, bleed hydraulics then put on new front springs. Dreading that.

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  18. KevZep

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    Yes your particular vacuum issue was a tricky one, good you found it though, something must have been niggling at you to keep investigating!!
    Agh....front springs, that doesn't sound like a fun job!!
     
  19. m.stojanovic

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  20. m.stojanovic

    m.stojanovic F1 Rookie
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    The idle speed does not seem to change when you change the bypass crews, thus I don't think changing the throttle butterfly gap from 0.05 to 0.03 will make any difference. I believe that the butterfly gap setting is there to just prevent them from "sticking" to the bore and that the bypass valve adjustment is to bring the IAC-s within range and to balance left-right, not really to control the idle speed.

    The idle speed is controlled by the ECU-s via the IAC-s. I suggest that you give the ECU-s a chance to "learn" (after all the "bad" running) and the idle speed should come down to normal. I noticed on my 348 that, after the battery has been disconnected and during the "learning" process, the idle speed will, from time to time, fluctuate up and down and then stabilise after about 10 min. of idling.
     
  21. KevZep

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    I totally agree with the throttle body comments, the gap is just to stop it sticking.
    In bold, this is exactly what my 348 did when I was working on the idle, I eventually started again and disconnected the battery and it went through this same process.
    Great info in this post.
     
  22. Ferrarium

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    Last time I did it I had to pop the tie rod and ball joint. Removing and replacing the springs is trivial once out, its getting them out that I hate, at least the fronts.
    But I'm putting ss lines in the front to match the rears so the brakes will not in the way at least. Getting the shick back is is a bit of a pain getting the bottom bolts in. Done it before when I did the shock bushings, I'd rather do cv joints.

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  23. m.stojanovic

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    I just removed both front struts to replace the shock bushings. I did not have to remove anything else other than the two bolts at the bottom. This is how I did it:

    1. Put the front on axle stands.
    2. Loosen the top nuts.
    2. Remove both bottom bolts (at each side); used a scissor jack under the lower ball joint to relieve pressure on the bolts; remove the adjustment shims.
    3. Keep the scissor jack under and carefully pull the lower ball joint somewhat out and jack it upwards until it clears the "fork" of the swing arm and the shock absorber bush, then move it and rotate its "forks" somewhat to one side to provide space for the shock bush.
    4. Remove the top nuts and manoeuvre the strut out; I think I first lowered the strut until the top 4 studs were out then could manoeuvre the bush "head" a bit outwards and over the swing arm "fork" (the swing arm can be pressed down a bit if necessary).

    Work in progress, one done one more to go (decided to replace the shock bushes even though they are only 31 years old):

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    Not too difficult using my home made bush extractor/installer (long M12 allen bolt and sockets). About to push new bush in:

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  24. johnk...

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    Glad it seems to be running right, but I have to say I'm confused. Regardless of how the depression tank is connected to the manifold, the manifold will pull a vacuum in the depression tank. The check valve you mention would be there to prevent loosing that vacuum when the manifold vacuum drops, like when you hit WOT. But if just idling it should be under high vacuum at all time. If connected backwards, because of the check valve, when the air injection solenoids open there will be no vacuum applied to the one way valves feeding the air injection rails. So, in effect, there would be no air injection. Since air injection is just to help warm up the cat, how does not having air injection make it idle funny?

    In a previous post you said that the car had this behavior before you took it apart, when it was cold outside. And apparently the vacuum line was hooked up correctly then. Are you sure that it just wasn't that it was warm out yesterday in NJ that made it run right?
     
  25. Ferrarium

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    The behavior prior was surging when cold yes, the MAF adjustment helped that condition quite a bit, once the cats were up to temp its was fine prior it would hunt a longer for sure. But the air injection issue was different, the conditions were similar so the got co-mingled until I realized there was 2 issues. I assumed it was the cold idle condition. You never hear the injection at all post reassembly instead the car bogs and surges. Once up to temp it stops but it takes a long time since its idling almost to a bog and engine shakes. The MAF adjustment made it better and it idled better but as soon as air injection came on it would be back.

    Now if I stopped the car and heat soaked a bit the cats when turned back on were warm enough the injection never came on and it idled fine so I assumed the MAF adjustment fixed it. If you just let it run the difference is you never hear the air injection growl, you hear solenoids click, no injection grown but engine immediately wants to die but ECU fights.

    Definitely not the air temps because I started it yesterday and the injection issue and it happened 20 seconds after start. So I knew it was something there as there was no injection growl. So air injection related... so I went back over the injection stuff and traced the lines and compared to the pics. I actually did find a post out there where someone confirmed if those hoses were wrong, and to mark them properly, or the system would not work right.

    I went and started it today, no issue. As a test I set the MAF's back to 383 and had the funky idle hunt when injection came on that you could hear the growl, but its just a hunt not a shaking bogging like the vacuum issue with no air injection growl which is a much worse form of it. Put MAF's back to 387 and it was fine.

    I think something funky happens when those hoses are reversed like air goes into the manifold from the exhaust or something, it sounds odd and holds no meaningful idle until the car goes into closed loop. Again takes a long time to it was hard to diagnose and I hated running the car like that.

    Most definitely sounds and feels like a vacuum issue to everyone's point but the issue is not a leak which was frustrating. In the end it was traced to something with air injection and the only thing it could be was vacuum leak (which I checked) or hoses routed wrong. It was the latter. Good thing I had pics. You know a good shop with 348 experience would have solved it and charged me 2K for watching the world cup and saying how hard it was to find.

    Miroljub may have an understanding of the issue if hoses are reversed, I can't explain the physics of it.
     

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