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It was the Alpha 278 version and I only saw it on the last test with the bad idle.
Hi Tom,
My best guess at the moment is whatever condition that caused the bad idle somehow also caused a longer than expected ICV period. If there was too much time between rising edges, the timer would overrun and start counting from zero. If this was the case, the period measurement could be smaller than the on-time measurement resulting in an open percentage greater than 100. I will review the code and at very least increase the maximum measurement time to mitigate this possibility. There are also a number of things that could be done to detect this kind of issue, even correct it in real time. The ICV signal also drives a hardware watchdog circuit that resets the DME in case the program crashes. This could be related to your bad idle issue, but there is no way to know for sure at this point. The OBD+ module can monitor the reset signal from the watchdog circuit, but the firmware has not been implemented yet.
Joe provided additional feedback on the odd ICV open percentages (> 100%) I've been seeing with this Alpha build, which is a developmental build. He said that it's possible some of the changes he's been making changed something in the ICV calculations. He suggested I uninstall that build and install the latest Beta build, which I did today.
I ran the engine again and everything looked normal, including the ICV values. After the engine coolant temperature was 190, I recorded 20 sec of data. The average idle speed was 818, which is in the spec range of 840 +/- 40. The ICV % Open averaged 85.9.
So, a lot of experimenting and testing to diagnose a weird idle condition that was fixed (knock on wood) by simply disconnecting and reconnecting the throttle switch. FWIW, the 951 has been parked in the garage for about 3 years, and before that my son had it stored in a rental garage for a year, so I guess enough corrosion built-up on the switch terminals to change the idle position resistance enough to trigger Full Load mode. Disconnecting/reconnecting the throttle switch for testing must have reduced the resistance to the DME into the normal range.
I'm still planning to verify the resistance to the DME and KLR when my multimeter arrives, but for now, all is normal.
I checked the resistances from the throttle switch to the DME and KLR: 1) DME Test
Throttle switch at idle - measure resistance between DME connector terminal 2 (throttle switch idle contact terminal 6), and DME terminal 19 (my choice for Ground). Result: 0.4 ohm. Spec value, 0-10 ohm. PASS
Throttle switch above idle - same test points. Result: open circuit. Spec value, infinite resistance. PASS 2) KLR Test
Throttle switch at idle - measure resistance between KLR connector terminals 22 & 23. Result: 607 ohm. Spec value 320-670 ohm. PASS
Move throttle slowly to full load, resistance should continuously vary. PASS
Move throttle to full load position. Result: 4.1xx Kohm. Spec value, 2.7-4.7 Kohm. PASS
So, it looks like I now have a new throttle switch to add to my spare parts stash.
Edit: So, now I still don't know what caused the Full Load condition at idle since the throttle switch tested fine. So, what was it, intermittent KLR issue, intermittent DME issue, OBD+ weirdness? Beats me.
Last edited by Tom Pultz; 11-02-2022 at 08:26 PM.
Reason: Add information
I was able to collect data to scale the NA 944 AFM voltage in terms of airflow. Assuming my math and measurements are correct, the maximum "measurable" air flow in terms of volume is about 250 CFM (7 m3/m). At 75F (24C) and 14PSI (96.5kPA) of ambient temperature and pressure, the maximum "measurable" airflow in terms of density is about 17.5lb/min (135 g/s). I plugged these numbers to a few online engine CFM calculators; this seems in line with the maximum VE you could ever reasonably hope to get out of a 2.5L 8-Valve NA engine.
The next step is to verify on the bench if the CFM (m3/m) calculations are identical at much warmer and colder ambient temperatures. If the temperature compensation proves to be accurate, then the ambient pressure compensation will also likely be accurate. However, I will not be able to prove that until I get to road testing and drive to higher and lower altitudes.
I was able to collect data to scale the NA 944 AFM voltage in terms of airflow. Assuming my math and measurements are correct, the maximum "measurable" air flow in terms of volume is about 250 CFM (7 m3/m). At 75F (24C) and 14PSI (96.5kPA) of ambient temperature and pressure, the maximum "measurable" airflow in terms of density is about 17.5lb/min (135 g/s). I plugged these numbers to a few online engine CFM calculators; this seems in line with the maximum VE you could ever reasonably hope to get out of a 2.5L 8-Valve NA engine.
The next step is to verify on the bench if the CFM (m3/m) calculations are identical at much warmer and colder ambient temperatures. If the temperature compensation proves to be accurate, then the ambient pressure compensation will also likely be accurate. However, I will not be able to prove that until I get to road testing and drive to higher and lower altitudes.
- Joe
Hi Joe,
😊. Can the final MAF range cfm be about 0 to 300 for those who have built a 2.8L stroker engine with a higher lift race camshaft.
My current stroker engine with stock camshaft was limited to HP output above 5500 rpm. I was using the Rogue NA MAF tune. The high lift race camshaft opens the intake/exhaust valves a + 0.030 inches.
Tom
Hi Joe,
😊. Can the final MAF range cfm be about 0 to 300 for those who have built a 2.8L stroker engine with a higher lift race camshaft.
My current stroker engine with stock camshaft was limited to HP output above 5500 rpm. I was using the Rogue NA MAF tune. The high lift race camshaft opens the intake/exhaust valves a + 0.030 inches.
Tom
Hi Tom,
It is important to draw a distinction between the amount of air the AFM can measure and how much can actually flow through it. It could very well be the 50CFM extra you are looking for will only occur with the WOT signal. If this is the case, the DME would be looking at the WOT table, and from what I understand, the AFM input is ignored.
If you actually did need more than 250CFM of measured air, you could possibly run a 944 Turbo program, AFM and Injectors. This can work because the Turbo 944 DME is completely unaware of manifold pressure, it is only looking at the amount of air entering the engine. In theory, you could just copy over all the NA 944 ignition maps. The fuel maps for idle and off-idle might also be ok, but the WOT table would definitely need an update. If this works, it would give you all the CFM you would ever need on a 944 NA.
One curious thing about the AFM is the maximum voltage it outputs is only 4.5 Volts. However, the analog input for that signal is capable of reading up to 5 Volts. I assume the DME program just doesn't support reading above 4.5 volts, but I don't know that for sure. In any case, eventually I will dig into the stock DME program and figure how it works. I should then be able to modify it to extend the maxim measurable airflow using that extra 0.5 Volts of dynamic range. I would then enable the OBD+ MAF controller take advantage of it.
I was able to cool my shop down to 59F (15C) and remeasured the air flow. The CFM calculations at 59F deviated less than 1 CFM over the entire air flow range comparted to the original 77F (25C) airflow measurements. This is extremely accurate, better than I expected and well within acceptable tolerance. Next, I am going to heat up the shop to as warm as I can make it. With any luck, the airflow measurements will have a similar tolerance and we can transition from bench testing to on-vehicle testing.
I was able to heat my shop to 85F and remeasured the airflow, the results were very good and in line with cool air testing. I also created a calibration table for the one off F9T-MAF-V2 reverse-flow MAF sensor/housing. I need write some more software/firmware, but it I could be doing on-vehicle testing as early as next week! However, I need to fix an issue with my 944 NA before proceeding. It is idling rich, and cold startup is very ruff like a cylinder is flooded but clears up after a few seconds. My guess is one of the injectors is leaking unmetered fuel into the intake port. I bought a set of used injectors off eBay and refurbished them. Pictures of this refurbishment are posted on the F9T Instagram page if anyone is interested. I will post more pictures as progress on this repair is made.
I'm working on hooking my MAP sensor directly to my new Sport DME. Sorry if I missed it, but is there a quick reference to match the MAP sensor output wires with the supplied DME plug-in (red, black, orange wires)?
I'm working on hooking my MAP sensor directly to my new Sport DME. Sorry if I missed it, but is there a quick reference to match the MAP sensor output wires with the supplied DME plug-in (red, black, orange wires)?
I'm interested in this also, and I would also like a recommendation on which sensor to purchase as there are tons of them on Amazon ranging from $15 to $70 or more. Also, if someone could share where/how they penetrated the firewall that would be very helpful too. Thanks.
I'm interested in this also, and I would also like a recommendation on which sensor to purchase as there are tons of them on Amazon ranging from $15 to $70 or more. Also, if someone could share where/how they penetrated the firewall that would be very helpful too. Thanks.
The penetration location depends on which side of the car the DME is located. The next step is to locate the hole in a 'free' space on both sides of the firewall. Sometimes there is room to thread the wires through an existing penetration that has a protective rubber/plastic seal around the opening.
Start drilling the hole with a small size drill bit. Then switch to a progressive drill that is V shaped to make progressively larger holes. Then hole is sized for the rubber/plastic insert of with the id for the wires wrapped in a protective sheath.
10-29-2022, 06:43 PM
