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Can you help me diagnose problem via FORScan w/ Laptop?

Discussion in 'Stock 2002 - 2005 Explorers' started by SyberTiger, February 7, 2018.

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    1. SyberTiger

      SyberTiger Active Member

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      Welp...my fast idle problem is BACK! :angryfire:

      I thought I killed off this problem about 14 months ago when I replaced the intake manifold where likely I had a slight vacuum leak causing air to get sucked into cylinders and then the computer increasing the fuel to balance out the air/fuel mixture.

      My vehicle idle has now jumped up from its normal 650 to 700 RPM to around 1,800 to 2,000 RPM. I'm thinking vacuum leak again but without following standard hose checking protocols I figures I'd hook up the laptop via my WiFi ODB2 adapter then run FORScan to see if I can get some hints as to why the computer thinks the idle should be this high.

      So far I can tell you that the CEL (check engine light) is not on and FORScan shows a DTC of P1000.

      I'm hoping someone can provide some input on specifically what parameters I should take a look at and provide ranges the data parameters should be within.
       
      Last edited: February 8, 2018
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    3. SyberTiger

      SyberTiger Active Member

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      Rather than clean the IAC first I thought I'd take a different approach and disconnect the battery to reset the computer to see if the idle speed issue went away. Oddly...or not, this did effect the idle issue I'm having. The idle went down to around 1200 RPM which still is not good but I let it the engine warm up to find out if the idle speed would settle down. As you know, it's not unusual for the engine RPM to jump up to 1200 RPM at first start but it should fairly quickly drop back down. After about 10 minutes the idle did drop but it's unusual it would take that long...it was near 80 degrees here in Florida today so there really wasn't much of a warm up time.

      I had FORScan up on the laptop and you can see two different snapshots I took. Right HERE these appear to be reasonable numbers as you can see the DESIRED RPM is 672 and the computer was able to get the RPM to 675 +/- 20. Does anyone know what the nominal IAC % is supposed to be? I had read that at 20% represents a fully closed IAC which is the same as if you unplug the electrical connector to it.

      Then there is THIS snapshot which shows the IAC % at 24.83 but the RPM is 747 instead of the target 672. This tells me the computer is trying to close the IAC to limit air in an attempt to get the RPM down to 672 (via air/fuel ratio). It was one of the snapshots I took after having reset the computer/battery and to me it might be an indication of a vacuum leak but I'm confused as to why five minutes later the RPM went down to 675 as shown in the first snapshot of the IAC/RPM.

      Anyone ever hear of an intermittent vacuum leak....and why did resetting the computer/battery fix my problem for now?
       
      Last edited: February 8, 2018
    4. SyberTiger

      SyberTiger Active Member

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      Anyone have any suggestions for other things to look for using FORScan that could be related or is it time to start looking for vaccum leak and rotted or cracked line?
       
    5. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      The PCM computes the difference between commanded engine rpm and actual rpm as measured by the crankshaft position sensor and stores the difference in keep alive memory. Knowing the difference allows the PCM to quickly achieve the desired engine speed. When the battery is disconnected the difference is lost and has to determined again which takes a while. The same things happens with stored fuel trims for various engine conditions. Removing the keep alive memory power resets all engine parameters to the factory settings and everything will have to be "relearned" which takes several drive cycles.

      I suggest stop disconnecting battery power and let the PCM relearn and save the stored parameters. Then monitor engine coolant temperature, engine rpm, TPS, fuel trims and closed loop. At cold start PCM should be in open loop for about 20 seconds while the O2 sensors heat up and the short term fuel trims will probably indicate a rich condition. When the PCM switches to closed loop the short term fuel trims should cycle slightly above and below neutral. The long term fuel trims can indicate if there is a vacuum leak because the fuel trim will be rich to compensate for the lean condition.
       
    6. SyberTiger

      SyberTiger Active Member

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      Thank you for the response....I've been fighting this for 5 years! Do you know where I can find the nominal values for fuel trim, TPS voltage, IAC percentage, etc. so that I can figure out what is out of spec. I had watched a video by ScannerDanner which seemed to imply that TPS should be around 1 volt or under for just about all Ford products that are fuel injection but having read THIS THREAD I get the impression that is should be lower.
       
    7. lincolnshibuya

      lincolnshibuya Active Member

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      here's a basic trick to figure out if you have a vacuum leak using forscan.

      graph the LTFT 1 and 2
      graph engine RPM
      graph the STFT 1 and 2

      you should have 7 graphs in that order

      now let the engine warm up say 5mins because it needs to be in closed loop for the fuel trims to be correct and active.
      rev your engine (or increase rpm to 3k) and see if the graph of fuel trims go up or down

      if the fuel trim graph goes down at high rpm (3k above) then you have a vacuum leak, if the fuel trim shoot up when going at idle (low rpm) then you have a vacuum leak.
       
    8. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      As I stated in that thread the 2nd Generation and later PCM employs a ratchet function for the TPS voltage. At ignition On the PCM assumes the TPS value is for closed throttle and stores it in keep alive memory. It periodically checks for a lower value and if found writes that as the closed throttle value. Some scanners report % instead of volts. WOT is around 5.0 volts so if closed throttle is 1.0 volts that would be 1.0/5.0 = 20%. If the closed throttle voltage exceeds a certain value the PCM sets a diagnostic trouble code (DTC). If the DTC is not set on your vehicle then the PCM is adequately compensating for your value.

      Fuel trims are reported in different ways for different scanners. Some are in + or - % and some are less than or greater than 1.00 Long term fuel trims are used to compensate for gradual wear and individual vehicle differences. When the values exceed pre-established limits the PCM sets a DTC. There used to be a website that lists Ford on board diagnostics (OBD) strategies for various years to meet Gov't emission requirements. I'll see it I can find it and post a link. I'm not very knowledgeable about IAC duty cycles and other IAC related parameters. The PCM controls idle speed with airflow (IAC valve) and spark advance/retard which has a faster response time. You might try cleaning the connection to your crankshaft position sensor by disconnecting and reconnecting the electrical connector a couple times. I looked at the values you posted and they looked fairly reasonable. Post the long term fuel trims. As I recall, the PCM will not update the LTFTs when the engine is idling in cold start.
       
    9. SyberTiger

      SyberTiger Active Member

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      Thanks for the suggestion. That would be 5 graphs not 7, correct?
       
    10. SyberTiger

      SyberTiger Active Member

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      Okay, thanks...I will wait to see if you can find the data but will perform the other things.
       
    11. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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    12. SyberTiger

      SyberTiger Active Member

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      Click HERE to see the graph. Anything odd or interesting that warrants a closer look? Please let me know what you think.

      Why is the general range for LTFT1 (-0.39 to +1.56) whereas for LTFT2 it's (-3.13 to +3.13)?
       
    13. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      In general the LTFTs seem very reasonable (within +/- 5%) for a vehicle that is 16 years old. Bank 1 (passenger side) initially is slightly lean (FT is positive +1.56 to compensate) but ends up just a little rich (FT = -0.39). Bank 2 (driver side) starts about twice as much lean (FT = +3.13) as bank 1 and ends up a little rich (FT = -3.13). I suspect the change from slightly lean to slightly rich is due to the engine reaching operating temperature (89 C). Both banks go slightly lean on throttle opening but not significantly.

      The only issue I see is the engine rpm does not match the desired rpm. With those differences an underspeed DTC (P1507/P0506) should have been set. Is there another parameter identifier (PID) like commanded engine speed to log?
       
    14. lincolnshibuya

      lincolnshibuya Active Member

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      yep, I got confused,, I normally do 7.. (the 02 sensors but in this case you don't need it)

      looking at your graphs I don't see any issues at all, RPM is close to 650 and your LTFT are healthy for a vehicle at that age. If you have a vacuum leak it will start very high at more than 15-29% (on some above 20% will trigger a CEL) and then go down as RPM is increased.

      when does it encounter a high rpm on idle (you mention 1,800 to 2,000 rpm) ? after it heats up or driving for a while?
       
    15. SyberTiger

      SyberTiger Active Member

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      Unfortunately, it appears that FORScan will only provide me with a list of PIDs when it it connected to the vehicle OBD port so I'll have to grab the laptop and put it in the vehicle and give it another shot to find out if it has the commanded RPM. I think the RPM you were comparing to was the desired idle RPM and it would seem that the PCM was doing a decent job of commanding the IAC to adjust the RPM to match the desired idle RPM value. From the graph you'll note the engine was started and allowed to idle for about 2/3 of the graph until the RPM matched the desired and operating idle of 672 RPM.
      1. That initial notch up on the LTFT 1 during open loop is curious and wonder what that is telling me regarding a problem area but perhaps it isn't important because it happens during the short open loop period?
      2. Is it normal and to be expected that the LTFTs jump up when the RPM is increased? And, what does the oscillation of the LTFT 1 tell us at the end of the graph when the engine is just idling?
      3. Are there any indications of a vacuum leak within the graph?
      4. Are the STFT graphs telling us anything other than the PCM and components are operating within range? The fuel trim malfunction thresholds are shown HERE but those are the combined thresholds that flag a malfunction; they do not give us an indication of the nominal and desired ranges. Looking through the Motorcraft Service OBD manual I didn't see nominal ranges listed.
      Appreciate you help!
       
    16. lincolnshibuya

      lincolnshibuya Active Member

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      on OPEN loop, the 02 sensors don't work so the engine run rich until they heat up and go into CLOSE loop, so ignore that.

      the LTFT jump of 2-3% is normal and even the spikes are probably just noise (somehow the scale is larger on LTFT-1) like what you see on '699.0 compared to LTFT-2

      I'm looking at the purple RPM graph for the actual engine RPM.

      However it will be interesting to see a longer graph because if you look at the STFT (1 and 2) something happened at '464.83, the graphs started to show different spikes and that's when your IAC% spiked a bit, so I'm not sure if this is temperature related or something got activated (fan clutch, ac-compressor, high load on the alternator..) might be useful to add the engine LOAD values too.
       
    17. SyberTiger

      SyberTiger Active Member

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      Before I changed out the intake manifold the high idle problem would usually show up after a week, or two, or four and generally the high idle problem might start out at 800 RPM, then eventually creep up to 1,500 or more over a period of several local drives...and, the high idle problem was usually evident after the vehicle was warmed up and I would be sitting at a stop light.

      However, after I replaced the intake manifold about 14 month ago I held my breath and waited several weeks and declared the problem was resolved...and every month that went by I was convinced the problem was solved. But, after 14 months it showed up again and then instead of by usual ritual of cleaning the IAC and throttle body plus disconnect the battery I decided to only disconnect the battery. The graph you see if after the battery disconnect and the apparent KAM being cleared. Now it's running just fine. I suppose I'll have to wait until the problem shows up again then run FORScan with all the PIDs to see if I can figure out what's wrong. For now though I was hoping you all could give me a clue as to what the likely problem could be so I can fix it without waiting for the problem to show up again. But, it sounds like, so far, everything looks good.
       
    18. SyberTiger

      SyberTiger Active Member

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      I can't remember what may have happened at the 464 timestamp. It's possible that I turned the headlights on (I was in the garage) so that I could see my dashboard gauges. A/C was off and would have expected an momentary RPM dip if that happened. Or, could it be that the CATs had warmed up enough to efficiently do their emissions job? I note that just before this the had been trending down as it was lowering the engine idle RPM while the engine was warning up then for some reason there was a bump up in the IAC...again, maybe recirculated engine exhaust and unburned emissions fuel being recirculated back after engine warm-up causing a richer situation? Maybe there's a EGR PID I could have included?
       
    19. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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    20. lincolnshibuya

      lincolnshibuya Active Member

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      I haven't tried playing with the EGR on my 02 mountaineer but I've tried with my 03 navigator (maybe that option is there). Forscan has the option to modify the duty cycle, I used the EGR test on Forscan because that EGR is located in an unreachable area to do visually or even do a manual vacuum check. There were 3 codes I got, one was a lean code, hose not connected on EGR and the famous EGR sensor failure. So I tried testing the EGR valve first if it's working by changing the duty cycle, the engine will almost stall (and rough idle) if you play with the settings. If the idle changes then the EGR valve is working.. (nice tool without disconnecting or using probes for troubleshooting) I did it end up with replacing the EGR DPFE sensor and the 2 hoses... fixed my lean and EGR error code
       
    21. SyberTiger

      SyberTiger Active Member

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      It sounds like nothing need be done until/if the problem shows up again but instead of resetting the PCM (battery disconnect) I should hook up FORScan and take a look to see what is driving the idle up. BTW, I've never had a DTC set whenever I've had the high idle problem. No clue at all....it just idles high. You would think the PCM would be smart enough to flag something when the vehicle has warmed up AND the idle is high AND the throttle has not been opened AND the IAC is commanded to be closed.
       
    22. SyberTiger

      SyberTiger Active Member

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      Okay....the high idle problem came back today and instead of resetting the PCM (battery disconnect) I went ahead and hooked up FORScan to see if I could find the problem. I only went on a 3 mile trip to the post office and halfway there at a stop light I noted the idle was now around 1,700 RPM. Click HERE to see the FORScan graph from 9 days ago after I had reset the PCM and everything seemed to run/idle fine. Now click HERE to see the FORScan graph taken today with the high idle problem active. You'll see in there that I punched up the RPM at one point to around 3,000 RPM.

      The differences I see today are several: The TP MODE is always at PT (part throttle) whereas in the first graph the mode is CT (closed throttle) when idling then PT when I push the accelerator. So the question is, what causes PT when I'm not pushing the accelerator. Is the cause the throttle position sensor or a vacuum leak? Also I note that long term fuel trim bank 1 is always sitting around +3.9 regardless of the RPM. Lastly, the IAC is commanded to be 68% the entire time regardless of idling or punching up the RPM.
       
    23. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      In the earlier graph the TPS voltage minimum was 0.90 volts. Since that was immediately after clearing keep alive memory (KAM) the PCM assumed that value to be closed throttle. In the later graph the TPS minimum voltage is 0.91 volts which is greater than the KAM closed throttle voltage so it is declared part throttle. The difference in voltage (1%) is not enough to significantly affect the idle speed. Since the throttle plate is not open (based on the TPS voltage) then air is bypassing the throttle allowing higher engine speed. The air flow could be due to the IAC valve or a vacuum leak. If the source is the IAC valve then the MAF sensor will detect the increased air flow and the PCM adjusts the fuel accordingly. If the source is a vacuum leak then the MAF sensor won't detect the increased air flow and the fuel mixture will be lean. I suspect there is a vacuum leak in bank 1 (passenger side) because LTFT is +3.91 now and was about +1 in the earlier graph. You could confirm the source by recording the MAF counts at normal idle and high idle. Make sure the engine load is the same: drive or park and A/C on or off. In my opinion, the only reliable method of detecting a vacuum leak is with a smoke machine.
       
    24. lincolnshibuya

      lincolnshibuya Active Member

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      doesn't look like a vacuum leak IMO.. could be an issue with the IAC and/or MAF. Vacuum leaks tends to make the STFT very high on idle and go down to 0 when at high rpm (you only need vacuum on idle)

      have you tried disconnecting the MAF when it's high idling?

      also try check if you can do an active test on IAC, if whatever percent you commanded doesn't reflect on how it idles then your IAC is defective..
       
    25. SyberTiger

      SyberTiger Active Member

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      Until I get the idle back to "normal" I can't go back and compare and contrasts the MAF counts so I'll hold off on that and not reset the PCM/KAM, etc.

      However, to see the impact of disconnecting the MAF and the IAC click HERE. I denoted the period the MAF was unplugged then the IAC unplugged. Unplugging the MAF had not make a discernable impact on the idle speed. Unplugging the IAC did by dropping the idle from around 1,800 down to 740 RPM. I note the PCM really didn't care about the unplugged IAC with regard to commanded percentage. I seem to recall that with the IAC unplugged the engine should stall or struggle maintaining a minimum idle RPM but that didn't happen. So, what's keeping the engine idling at 740 when the IAC is unplugged? Could it be the IAC is stuck open?

      I'm fairly new with FORScan so I haven't delved into how to change the IAC commanded value. Can you provide some data on that?
       
    26. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      When the MAF sensor is disconnected the PCM relies on the TPS voltage to estimate air flow.

      On my Sport I adjusted the throttle stop so the engine speed is less than normal but not low enough for the engine to stall. That way I can detect when the IAC valve has failed but still drive the vehicle. You may be recording the wrong PID for commanded idle speed. In my tune there are multiple commanded idle speeds: vehicle not moving in park/neutral vs drive; A/C on or off, vehicle moving with closed throttle. Have you seen any change in commanded for any of the previous configurations?

      If your IAC valve were stuck open the engine speed would be well above 740. If it were stuck closed your engine speed would not reach 1,800 rpm at closed throttle. I suspect your IAC valve is defective and not responding correctly to PCM commands. I had to replace the one on my 2003 V8 recently because the engine was stalling. I tested it with a battery charger and it sounded like a buzzer.
       

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