Random RPMs drop, engine seems want to stall

[JWKberlin]

Did several screen shots of the oscilloscope

Thanks a lot mate!
That is indeed helpful. I might need a bit of background The Figures 2 - 4 are more or less steady state, right?
The first one is quite interesting, though. In that first screenshot did you come from higher rpms and the over-swing (to 521 rpms) resulted from that, or was it also steady state? And is that over-swing (in case it was a drop) repeatable/ typical?
In terms of amplitude, it is pretty close to the behavior of mine, but the time scale is totally different, yours appears to recover within 50 - 65 ms, while mine takes 2500 - 3500 ms ... what is wrong here, I wonder.

Kind regards, Janosch

 

[Explorer75]

Thanks a lot mate!
That is indeed helpful. I might need a bit of background The Figures 2 - 4 are more or less steady state, right?
The first one is quite interesting, though. In that first screenshot did you come from higher rpms and the over-swing (to 521 rpms) resulted from that, or was it also steady state? And is that over-swing (in case it was a drop) repeatable/ typical?
In terms of amplitude, it is pretty close to the behavior of mine, but the time scale is totally different, yours appears to recover within 50 - 65 ms, while mine takes 2500 - 3500 ms ... what is wrong here, I wonder.

Kind regards, Janosch

I did all the captures in parking.

When I had the rpms drop the vehicle was moving or on D, usually in stop and go heavy traffic. After the TB replacement that problem is gone.

One thing I noticed when doing a complete PCM reset (+ and - cable short): with the old TB it would oscillate very badly on first cold start up and stabilize after 15 seconds or so. With the new TB right after reset it is steady as it can be. This is when I could be 100% sure the old TB has some faults. On a recent trip I had better fuel economy (like +1 mpg) than before, it could be just coincidence.

 

[JWKberlin]

I did all the captures in parking.

Would you mind to do one more in N, just pushing it to about 2k rpm, then let go the pedal and capture the rpm behavior while doing so. (while it goes down or beyond 600 rpms). The engine should be warm though. That would be cool.

And you are sure the first shoot you took, with the rpm going down to about 520 rpm was normal idle? No cold engine or anything - I am just wondering; would not expect such a drop.
Well, I am facing a major service anyway and I may decide to swap the TB just as a try - if it does not help, I do have a spare; the ford electronic TBs do not seem to be perferct, so not bad to have one left.

 

[Explorer75]

OK, conditions: Vehicle in Neutral, fully warmed up, NO a/c (A/C only in the last as noted)

1) 2k rpms held, let go the accelerator and rpms dropped to about 300, stumble felt similar to fault first reported before replacing the TB.

2, 3 and 4) Subsequent drops from 2,000 rpms could not replicate 300 rpm drop/stumble, like PCM calibrated for it, smooth transition to 600 rpm can be felt.

In the next one rpms dropped to 447, no stumble felt, smooth operation. Seem like the problem presents or is felt below 400 rpms.

This last one I turned on the a/c, rpms dropped to 500ish on compressor start, smooth operation felt (no stumble of any kind felt). Then rpms went back up to 600ish.

 

[JWKberlin]

2k rpms held, let go the accelerator and rpms dropped

Thank you very much for all those plots - now it is getting really interesting.
As can be seen from the plot I shared your and my engine behave quite similar - at least when not taking your first plot into account. Man, this looks strange ... and a drop down to 300 rpms is somewhat scary (at least if it happened to me). I am really wondering whether the TB replacement really addressed the root cause of your initial problem or it may reappear sooner or later.
The Plots 2, 3, and 4 on the other hand sort of suggest that there is not really a problem. Compared to mine, I just noted a slight (and occasional) difference in the amplitude (your's goes down to approx. 450 rpms, while I noticed "only" a drop to 470 on mine) and timescale (your's may take a second longer to stabilize than mine). But I would conclude for certain, that either none of us has any issue - or we both have the same one.
I will certainly monitor mine for a while to figure out whether the issue evolves.

I am not sure, I ever explained the background as to why I am so "picky" about exactly this rpm setting: Although, in normal gasoline use I never had any significant issues apart from the rpm situation exactly as you have now shared it. But I am using also - as alternate fuel - LPG which is known to react more sensitive to any kind of sub-optimal engine settings. While using this, I faced exactly the same stalling issue you observed also on gasoline and on your engine. This is why I believed we could have the same issue - mine being less severe yet, but may worsen. Let me know, in case the stalling re-appears, please - as I will do, in case it re-appears on mine.

And again, thank you very much for all the good data and the time invested to capture these - I really appreciate it. If I can anyhow help you, just let me know.

 

[Explorer75]

I found this you tube video

https://www.youtube.com/watch?v=xU-z8Myhsc0

Mine doesn´t have that, in 2018 when I bought the truck I went to the dealer to update all the modules to the latest calibration, it seems they did.
If you experience that then you need that tsb done, which is to reprogram the PCM to the latest calibration.

Besides that moment when the rpms went down to 300 I haven´t noticed it again, hopefully the PCM learned from it.

As for the LPG conversion, they can be a pain in the a$$. They are done here a lot in my country and the give a lot of problems usually because of cheap systems that can´t match sophisticated electronics with the latest vehicles. I´ve been told that Tartarini LPG conversions are supposed to be the best and also the most expensive. Here they are even endorsed by dealers and the vehicle maintain power train warranty.

Anyway, I´ll post again if the rpm drop happens again. Hopefully it won´t.

 

[JWKberlin]

The issue explained in the video - I never experienced on mine, but also appears to have not so much impact at all, at least not in my use cases. Even if it had, I would most likely not have noticed it so far. But it is good to know and look out for this issue.

As for my LPG add-on: it is a Prins VSI 1 system installed in late 2011. The system is very sophisticated. It has still the Japanese Keihin injectors as full metal version and this late version of VSI 1 has already fixed all issues known since it's introduction. Thus altogether, I am quite happy with it, and the maintenance is adequate: basically to check/replace filters every 18k miles.
A photo of it below:

I am pretty convinced of the system. For sure the photograph shows only the injectors, in case of interest I can take more.

They are done here a lot in my country

By the way, I am from Germany. And based on the quoted passage I have the feeling you are not in the US. Where are you from, if you'd like to answer?

 

[Explorer75]

The issue explained in the video - I never experienced on mine, but also appears to have not so much impact at all, at least not in my use cases. Even if it had, I would most likely not have noticed it so far. But it is good to know and look out for this issue.

As for my LPG add-on: it is a Prins VSI 1 system installed in late 2011. The system is very sophisticated. It has still the Japanese Keihin injectors as full metal version and this late version of VSI 1 has already fixed all issues known since it's introduction. Thus altogether, I am quite happy with it, and the maintenance is adequate: basically to check/replace filters every 18k miles.
A photo of it below:


I am pretty convinced of the system. For sure the photograph shows only the injectors, in case of interest I can take more.


By the way, I am from Germany. And based on the quoted passage I have the feeling you are not in the US. Where are you from, if you'd like to answer?

I´m from Dominican Republic.

I would add a LPG or CGN (Natural Gas), but I don´t drive too many miles per year, maybe just 5,000.

I´ll report back if the problem returns.

Good luck!

 

[JWKberlin]

Dominican Republic - sounds like summer all year. Here in Southern Germany we had last Tuesday the first snow and temperature is still at around 0°C *shiver*
Say hello to the sun from me
By the way, after doing all sorts of maintenance (filters, spark plugs, etc) I went last weekend to a specialist for the LPG and he did some slight changes to the LPG system (parameters adapted only). Since then I am driving happily and without further stalling or issues on LPG for 100 miles.
But for sure I will also report back to you in case something similar happens to mine.

Good luck to you as well!
Kind regards,
Janosch

 

[peterk9]

My friend had his Mustang fixed up to run on propane back around 1970.

Peter

 

[Explorer75]

Dominican Republic - sounds like summer all year. Here in Southern Germany we had last Tuesday the first snow and temperature is still at around 0°C *shiver*
Say hello to the sun from me
By the way, after doing all sorts of maintenance (filters, spark plugs, etc) I went last weekend to a specialist for the LPG and he did some slight changes to the LPG system (parameters adapted only). Since then I am driving happily and without further stalling or issues on LPG for 100 miles.
But for sure I will also report back to you in case something similar happens to mine.

Good luck to you as well!
Kind regards,
Janosch

Thanks

I´ll sure be posting for better or for worse.

 

[Explorer75]

UPDATE

Got a message on the dash "Check fuel fill inlet" ODBII code 0457. A quick search led me to a video where it is recommended to clean the capless fuel inlet with the funnel that the truck comes with and WD40. Spray the WD40 and use the funnel 20 or 30 times to clean and lubricate the fill hatch. Code didn´t go away. Found a thread in this forum about someone having the same issue and the dealer replaced the canister purge valve. replaced the valve and code went to pending, erased it and haven´t got it since. Now the interesting stuff, going back, after I replaced the throttle body I got the low rpms maybe 4 or 5 times. A lot less than before where in a single drive it would do it a dozen times. After replacing the canister purge valve it never did it again, so it got me thinking and did a test, put back the old throttle body and surprise, surprise, the problems seems to be gone. It seems it was the purge valve and not the TB. I will do the RPM log with the forscan again but so far the rpms do feel a lot more steady and I´ve never seen them at 500 or below.

 

[Dlojack]

Recently I´ve been noticing a random drop in rpms, below 500. At first I noticed it on D on stop and go traffic, the engine seems to want to stall briefly, then the rpms got back up to 600+. Then today it happened at Parking. I turned the A/C on and off and the rpms seem unchanged, So I don´t think it has to do with the A/C.
All maintenance is up to date (almost 60K miles on the truckl: new motorcraft spark plugs 5k miles ago, new air filter 2k miles ago, new oil a month ago, cleaned throttle body couple of months ago, check engine codes, no pending codes. The only thing I can think of is a failing TPS within the throttle body.

What do you guys think?

,

Try cleaning the mass airflow sensor you should do that every time you change the filter they have a special cleaning solution so you don’t damage it

 

[peterk9]

Thanks for the update Explorer75. Might be helpful for others having a similar issue.

Peter

 

[peterk9]

Try cleaning the mass airflow sensor you should do that every time you change the filter they have a special cleaning solution so you don’t damage it

As reported, replacing the canister purge valve seemed to have fixed it.

Peter