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Throttle Bodies Show Increased Lag with Age

Discussion in 'Technical Q&A' started by EastMemphis, Aug 14, 2020.

  1. EastMemphis

    EastMemphis Formula Junior
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    May 25, 2019
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    I made a tester to determine what is wrong with the drive-by-wire system in my 360. We deduced that the failure was with the throttle bodies (TB), one or both. The ideal thing would be to buy two new throttle bodies and an accelerator potentiometer (AP) and just replace everything. That's probably what would happen if I brought the car into a Ferrari dealer and probably most independents too.

    I didn't want to just go spend $4000 on parts. A TB for the 360 is $1750 at Ricambia, and I need two. Plus another $400 for the AP just to be sure.

    I spent a lot of time figuring out exactly how the drive-by-wire functions. It's really quite interesting how the system works with several levels of checks and balances. It's an important system with important safety considerations.

    I had two goals for this project:

    1. Determine what's wrong with the existing set of TB's.
    2. Determine if they can be repaired or rebuilt rather than just replaced.

    The tester is based on an Arduino with an LCD, SD card, and the usual input and outputs of a stock chip. The software was a lot more involved to setup than the hardware. I was mostly concerned with these things:

    1. Are all the gears and moving parts fully functioning?
    2. Are the potentiometers (there are 2) working properly?
    3. How much lag is there from zero to full throttle?
    4. How much power does the motor consume?

    Once I got the program up and running with an old TB from my 360, I run it on a new one and an eBay special for the 360.

    Here's the graph from the data:

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    The volts are from the TB potentiometer #1 which goes from low to high volts as the throttle plate moves. The line chart above is taken from 5ms data and is very clean. The line stops when full throttle has been reached.

    As indicated, the new throttle body had considerably less lag going from idle to full throttle. The two old ones nearly matched each other in lag. Both were from similar mileage and year cars.

    I'm left wondering if this throttle lag would detract from performance of the car?

    Rebuilding...

    After careful visual examination, I determined that the only difference between a run of the mill Bosch 0 280 750 XXX and the one for the 360 (an "038") is a vent. This is the one that pumps oil into your intake if you overfill your car with oil. Besides that one little physical difference, the series of TB's that the 360 is part of are virtually identical.

    I found a nice TB for a Porsche on Amazon that had the exact same dimensions as the 360's TB. It's a model #474 (vs. 038 for the 360). Same size everything. Same connector. Same mounting holes. Could it be a source of spare parts? At less than 1/10th the cost of the #038, worth looking into.

    My next project will be disassembling the old eBay specials I bought and rebuild them with new parts from the Porsche TB I got from Amazon. I'll know the answer to this question soon.
     
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  3. tbakowsky

    tbakowsky F1 World Champ
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    Sep 18, 2002
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    I have always considered the Porsche t-body as a potential replacement..however I have never needed to replace a throttle body on a 360 as of yet. They have proven to be a very reliable unit. Same as the Porsche.
     
  4. EastMemphis

    EastMemphis Formula Junior
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    While they may be mostly reliable, are you confident your throttle bodies are performing up to specification?

    If they're original units, they are likely inducing lag into your performance curve.
     
  5. tbakowsky

    tbakowsky F1 World Champ
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    I think you are looking for problems where there are no problems. Everything has a life span and degrades over time..no matter what it is. Replace when it fails. Stop looking for pixie dust.
     
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  6. EastMemphis

    EastMemphis Formula Junior
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    #5 EastMemphis, Aug 14, 2020
    Last edited: Aug 14, 2020
    So you wouldn't want to know if your expensive throttle bodies are about to fail or potentially cascade failures in other, even more expensive systems?

    While these throttle bodies have been holding out for nearly 20 years, they are getting older and wearing out. As the TB motors age, they require more amps. If the motor gets to the point that it's sucking too many amps out of the ECU, it can and will fry the most expensive electrical component on the car. The ECU won't "fail" the throttle body, the throttle body will fail the ECU.

    So by your logic, forget about the pixie dust problems that aren't failures. Wait for something to break first. Great.
     
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  8. tbakowsky

    tbakowsky F1 World Champ
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    Pretty much yea..stop looking for problems. Deal with the issue as they arise. Throttle bodies are not an issue on the Ferrari. Lambo for sure.
     
  9. EastMemphis

    EastMemphis Formula Junior
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    News flash for you: I have at least one bad throttle body on my Ferrari. So ya, throttle bodies are an issue in my small Ferrari world.
     
  10. MCASEY

    MCASEY Rookie

    Apr 1, 2015
    41
    Sydney Australia
    If you hold the throttle flat at gear changes, do the TB's close and then reopen?
     
  11. EastMemphis

    EastMemphis Formula Junior
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    That's a function of the ECU, something that's outside the scope of my investigations.
     
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  13. Some Guy in the sky

    Sep 19, 2018
    140
    I'm actually seeing something similar. Over the last two years I have slowly replaced almost every bosch part on my engine. Every time I have replaced something I have noticed an improvement in one aspect or another. I think we are in uncharted territory with these cars as they get into their second decade and we probably need to rethink what are maintenance items 20 years on.

    What follows is a list of what I replaced and when on my 100% stock 1999 360:

    1) Coils were original, replaced all of them and noticed a great improvement in power and responsiveness at 20-ish k miles.
    2) Replaced both MAFs a few months and a few hundred miles later (they had been replaced 10 years previously) . Again great improvement in power, I highly recommend this if your MAFs are 10 years old or older.

    3) replaced all 4 02 sensors a few months and not many miles after the MAFs (date codes of 1998). Noticed reduced exhaust smells at idle.
    4) Had injectors ultrasonically cleaned. Testing showed they were very unbalanced in output volume. Cleaning and post testing showed they were also clogged and output volume per time was increased by 20% (March 2020). Now the car seems to go to redline effortlessly. It also feels as if it could easily keep going past redline if it were not for the fuel cut off rev limiter. The car now feels like a divine wind (typhoon) is blowing against a sail pulling it instead of a being pushed by a mechanical device.
    5) Replaced both crank position sensors about June of 2020, noticed smoother cold idle as well as more stable oil temperatures under similar driving conditions. There also seems to be less heat when I open the hatch after a drive (I always hit redline many times during a drive). It also seems that the exhaust valves open more readily but I have no way of really measuring this. About 21k miles in.

    6) Replaced both exhaust cam position sensor a week ago, noticed better responsiveness at lower rpms. Just under 22k.

    After changing all of these items my car went from having flat spots in the power band with erratic responsiveness to a screaming demon that pulls hard through the majority of the rev range. The car was under the same owner ship for 15 years before I bought it and always maintained at highly regarded shops so this was not a poorly maintained car (records show 5 figures worth of work over the 5 years before I bought it in 18 even with records going back to 99), Once I bought the car I had the belts, plugs and all gaskets involved in a major replaced and the cams properly timed by a highly regarded shop in my area. This took place before I changed any of the above items.

    I am actually currently investigating a rare but annoying lack of reaction from the gas pedal when I try to rev match (stick shift) at lower rpms on down shifts. Every once in a while I will tap the gas to raise the rpms and I will get zero response ( as in the rpms don't move at all) then I will repeat and everything will work fine. I was going to start to investigate the potentiometer but it seems you have beat me to the punch.

    I would say keep going and share with us what you find. The improvement in performance that I have seen from making the above changes have been great and make the car extremely enjoyable to drive now. There is no way I will ever sell it and I would suggest others look into the above changes not matter how many miles and what kind of maintenance the car has had. You can buy most of these parts outside of the Ferrari network for cheap.
     
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  14. EastMemphis

    EastMemphis Formula Junior
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    One symptom I've had is sometimes when I stomp on the gas, the car feels like a turbo and has a lag before anything happens. It's just a few 10ths of a second but to me, alarming. I started getting trouble codes indicating problems with the drive-by-wire circuit and here I am.
     
  15. MCASEY

    MCASEY Rookie

    Apr 1, 2015
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    Sydney Australia
    Sorry, I thought you may be viewing in real time. Ciao.
     
  16. EastMemphis

    EastMemphis Formula Junior
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    An evolution of my tester is to hook it up between the throttle body and the ECU and monitor the current flow, lag and reaction of the pots as they perform in real life. It's not that big a leap technically. I have both the male and female connectors for the throttle body so it's just a matter of a few minor circuits and some software to be able to do this.

    Here's a video of the tester working...

     
  17. f355spider

    f355spider F1 World Champ
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    May 29, 2001
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    The accelerator pedal and throttle body do wear out. I have a Bosch drive by wire system on my older BMW and have replaced both components over the years (at separate times) when I received the relevant Pcode and driving issues. I have 314,400 miles now, engine and trans have never been rebuilt. Easy DIY to swap out. Surprised they would show significant wear at such low mileage on a Ferrari. I would wonder how significant the laggy response time is in actual use, and whether that is considered "normal" or not. In other words, how soon do they become laggy....does that happen immediately, or slow over the decades?
     
  18. Some Guy in the sky

    Sep 19, 2018
    140
    This is a good question and I would like to know as well. I will start having my mechanic start testing this at every yearly inspection/service once I find out if my existing ones need attention or not. Unfortunately its only going to take 20 years to get a an answer.
     
  19. EastMemphis

    EastMemphis Formula Junior
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    I'd say the average Ferrari throttle body gets a lot of banging up and down, vs. a road car that might drone on for hours at one throttle setting.

    The engine compartment in a mid-engine car is a lot hotter than front engine cars. Age and heat alone can degrade the insulation on the motor windings. The pots can oxidize and the lubricant between the pot and the pickup can dry out or be pushed off the moving surfaces. The device itself is unforgiving of tolerance so degradation can and will cause these devices to cause trouble codes yet still appear to function.

    There's also this mystery about these devices. People I've discussed this problem with have seemed to consider the TB to be a mystical device that simply must be replaced (in pairs) when they show any sort of trouble. The actual workings of the device and failure modes are a lot less well known and repairing and rebuilding them is unheard of.

    I think the biggest threat TB's raise is the possibility of melting the ECU from drawing too many amps. I discussed this with 360Trev and that's his concern. As they age, they draw more amps and once they cross some threshold, I think it was 6 amps, they literally will start melting the solder in the ECU. I'd like to get ahead of that possibility by understanding how these things work, how to test them and how to rebuild them using inexpensive parts.

    These devices are tough as nails but when they get to a certain point, they are going to cause problems. I suspect that I'm on the leading edge of that problem curve and in the coming years, throttle body failure will be as common as leaky fuel pumps.
     
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  20. Some Guy in the sky

    Sep 19, 2018
    140
    This guy might be worth talking to. Seems he only works on Mercedes, but I think he probably knows Bosch TB's fairly well.
     
  21. EastMemphis

    EastMemphis Formula Junior
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    Interesting findings...

    I added one more test to the program to find out what minimum duty cycle (MDC) is required to move the throttle to full. The motors run on a signal called PWM or Pulse Width Modulation. The PWM signal is just a square wave. The duty cycle represents the percentage of time that the top of the wave, the high volts, is on.

    The MDC test starts out at 0 and gradually builds up until the throttle moves all the way to fully open. By going very slowly, the inertia of the valve in motion is removed from the equation. It's a gentle push that gradually gets firmer.

    Comparing MDC's between throttle bodies (TB) is quite a good test for health. A low MDC indicates a minimum amount of friction in the system and an efficient motor. A high MDS indicates the system has major issues such as friction in the gears, shorts in the windings, worn brushes and other things.

    I ran the five TB's I have sitting around my desk (the sixth is still in the car) through the tester and the results were eye opening.

    New TB's, Bosch part 0 280 750 474 (Porsche) MDC = 26 mA=3025
    New TB's, Bosch part 0 280 750 474 (Porsche) MDC = 27 mA=3098
    eBay used TB Bosch part 0 280 750 038 (360) MDC = 35 mA=2525
    Old TB, left side Bosch part 0 280 750 038 (360) MDC = 37 mA=2415
    Old TB, right side Bosch part 0 280 750 038 (360) MDC = 61 mA=2537

    The milliamps are the maximum draw during the test. I suspect the new TB's with their new brushes, can pass power to the windings more efficiently than the 20 year old brushes in the 360 TB's. The current draw in two of 360 TB's are about the same as is the MDC and lag time. The "old right" TB has a much higher duty cycle requirement, probably from worn brushes.

    My prognosis is that the right throttle body is out of specification. I changed the left one already with an eBay special, my first attempt to "guess" my way out of this problem. After 100 miles, the trouble codes came back so either I guessed wrong, purchased a bad TB or both TB's are bad. After running these tests, I believe I can say that I guessed wrong. If I had changed out the right TB, I might never have gone down this path.

    I managed to buy the second TB from the seller of the first and they came from the same car. I'm going to pull the first eBay unit out, test it and then come up with a matched pair to install in the car. That should solve the TB issue. At least I hope...
     
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  22. EastMemphis

    EastMemphis Formula Junior
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    I've been talking to 360Trev. He seems to know everything. Very helpful.
     
  23. EastMemphis

    EastMemphis Formula Junior
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    I removed the eBay replacement I had in the left side of the engine and tested it. A bit weak, but not much different. It had a MDC of 41. I decided to use the original left TB (MDC 37) and the new eBay TB (MDC 35) as they had the closest MDC.

    After installing them, I reset the Throttle Adaptation using an Autel MS906 and took it for a test drive. All good, no codes. Car was a lot smoother with balanced TB's.

    After returning, I checked the codes again and all clear. I really won't know if this issue is resolved until I put at least 150 miles on the clock. Did 10 today. 140 more to go.

    In the meantime, I'm going to rebuild the two rejected 038's I have using parts from the 474's. Once that's complete, I'll swap out the rebuilt ones and see what happens.

    Here's a nice picture from the Autel:
    Image Unavailable, Please Login

    The time slices are 0.5 seconds so pretty coarse. Notice the relationship between AP #1 and #2. #2 is always half of #1.
     
  24. 24000rpm

    24000rpm F1 Rookie
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    oh, if, just if, there's a step by step tutorial on how to test these throttle bodies........ like , how to hook up with Arduino and what version of Arduino and what supporting equipment to buy.
     
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  25. Ferrari Tech

    Ferrari Tech Formula Junior

    Mar 5, 2010
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    Wade Williams
    I have always felt that driving a stick 360 was a challenge due to the fly by wire throttle. It always felt like it was behind what I wanted it to do. If I owned one and didn't just test drive them on occasion then I expect I would adjust to it. I am constantly finding new things that are required service as these cars get older. I have often thought the next steps of repair/maintenance on these more modern cars would be a more in depth electronic analysis system. I for one am glad to see someone with the skill needed taking steps to guide the future of maintenance. And further more actually sharing his knowledge. I will be watching and listening.
    EastMemphis, if I can be of any assistance, please feel free to contact me. I believe you are on the right track with this one.
     
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  26. EastMemphis

    EastMemphis Formula Junior
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    I put another 30 miles on the car. Ran even better today. Idle was smoother and acceleration brisk. One oddity. I noticed it was much harder to hold 2000 RPM's in first gear on a rough road. I've had no problem with throttle phlugoids (that bucking action in low gear, mid throttle) with the 360 up to now. A "Phlugoid" (actually, an aviation term) happens as a result of the operator's foot reacting to the motion of the car. Foot presses gas. Car bounds forward. Foot comes off the pedal slightly. Car de-accelerates. Foot moves forward again and the cycle continues. Usually getting worse until the pedal is either smashed to the floor or released.

    After a couple minutes of concentrating on the problem, my foot learned how to deal with it. A potential test for problems with the drive-by-wire system might be to try and hold the throttle at 2000 RPM's on a bumpy road in first gear. If you can hold engine speed without concentrating, you either have a very well trained foot or your throttle bodies are damping out the phlugoid oscillations.

    I've got a total of 40 miles on this fix. 110 more to go.
     
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  27. Some Guy in the sky

    Sep 19, 2018
    140
    I had something very similar but the bumpy road was not required. It seemed to get better when I replaced the MAFs and totally went away once I replaced the crank position sensors.
     
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  28. tbakowsky

    tbakowsky F1 World Champ
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    Sep 18, 2002
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    So if you the average customer were told your throttle bodies need to be replaced because they are aging.. yet still work fine, would any of you pony up the cash? Or would you think the shop was trying to rip you off..

    I can't replace anything on a car unless I can prove it's bad. I have a 99 360 in the shop right now with over 100k miled on it and the throttle bodies are the original units. Should I replace them even though the car runs just fine as it is? Would YOU replace them if the car runs just fine? Put your money where your mouth is.
     
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