I was Wrong about EGR and Part Throttle Detonation

[vristang]

I have made several posts about how removing the EGR without disabling the function in the computer would cause part throttle detonation due to advanced ignition timing.

It turns out this is wrong, and I want to get the correct info out there.

The computer does see when the EGR is not functioning properly. When this happens the computer enters an alternative strategy, which eliminates the fuel and timing compensations that are usually made when the EGR is working.

I have yet to figure out all the details on the "Alternative Strategy", but I think it safe to say that Ford would have made these settings rather conservative.

This was pointed out to me by Joel5.0 from MustangForums.

I have confirmed with the Ford EEC-IV GUFB Manual that this is accurate.

Here is a summary of when the Failure Mode Strategies are used.

jason

 

[vristang]

Here is a Corrected Full Write-up on the EGR

EGR Theory and Notes on Removal​

Vristang​

Background-
The EGR (Exhaust Gas Recirculation) is an emissions device that reduces NOx by decreasing the combustion temperature. NOx (Nitrogen Oxides) are only formed when enough Oxygen and Nitrogen are present and combustion temps are very high. Small reductions in combustion temps can have large effects on NOx output. EGR reduces combustion temps by displacing Oxygen from the intake charge with an inert gas (Recirculated Exhaust). The decrease in Oxygen lowers the efficiency of the combustion process, and therefore the peak temperatures reached during combustion are lower.

The Effects of EGR-
Due to the decrease in the efficiency of the combustion process, the EEC-IV computer will increase spark advance when the EGR is functioning. The loss in overall efficiency experienced due to EGR can be somewhat offset by this increase in ignition timing.

Since the efficiency of the combustion process is being decreased, less power is being created. This will cause the driver to open the throttle body a little more, in order to maintain an appropriate level of power for the driving situation. An open throttle body is easier for the motor to breathe through - the pumping losses are lower.
Due to the fact that the spark can be advanced and that the throttle can be opened farther (reducing pumping losses), one can actually see a gain in fuel economy due to the use of EGR.

Also worth mentioning is the coolant system that runs to the EGR or EGR spacer. The EGR gasses are rather hot when they hit the intake manifold. The coolant in the EGR spacer helps to lower the temperature of the exhaust gasses before they hit the fuel. If these coolant lines are removed, the extremely high temps of the exhaust gasses, mixed with the intake air/fuel charge can lead to part throttle detonation and/or backfiring. Ford used the coolant to lower the temperature of the exhaust gasses to a reasonable level.

Also, note that the EGR will only function at part throttle conditions. The EGR is turned off at WOT, and therefore has little affect (if any at all) on WOT power.

Summary-
The EGR system does not affect WOT power, and can even improve part throttle fuel economy.

Removal of EGR-
Popular belief has been that removing the EGR system and not disabling the function of the EGR in the computer, would lead to part throttle detonation due to the increased ignition timing. For this reason it has been said that the only safe way to eliminate the EGR was to also get a chip or custom tune that disabled the system in the computer.
It turns out that this is not true.
The EEC-IV can recognize when the EGR is no longer functional, and will use alternate fuel and timing strategies when this is the case. There is very little risk of harming the engine by removing the EGR equipment from your EEC-IV vehicle.

Here is a summary table of the alternate strategies used by the EEC when a bad sensor signal is detected (code condition is triggered).

Myth –
Some folks misunderstand what the EGR is, and will tell you that the EGR pulls the exhaust into the combustion chamber to burn any unburned fuel in the exhaust, thereby reducing Unburned Hydro-Carbons. This myth seems to have originated in the days of carburetion, when the understanding of emissions by the public was still rather poor. Remember, the EGRs primary function is to reduce NOx.

This site has some info on the EGR plug which can be used to prevent the check engine light from coming on after disabling the EGR system. http://fordfuelinjection.com/index.php?p=61

 

[VG30DE]

Thank you, its about time this was publically published. The main reason to get rid of the EGR is to safely do a coolant bypass of the EGR spacer block, thus keeping the plenum cooler, and to stop exhaust from flowing through the plenum because it literally clogs it up. There is literally no performance gain or loss from disabling the EGR except as a result of those conditions since the EGR is not open at WOT.

I had my GT40 intake extrude honed and polished 3 years ago. I've been running with the EGR valve and sensor in place and the wire harness connected but the vacuum unplugged. If I pull my intake right now, its still clean and shiny inside. Not the case if I had EGR. And like most of us here, it doesnt pass emissions anyway.

 

[smittyb]

I almost said something last time you said it, but I had nothing to back it up.
VG30DE, just curious, but you still have exhaust gas up to the spacer, the valve is just not opening, correct?

 

[vristang]

You guys knew I was wrong and you didn't say anyting.

NO Worries


Bump to make sure this is seen by anyone who may care.

 

[TENGRAM]

great info. that GUFB document is good stuff, albeit lengthy. nice summarization of the EGR info

 

[HISSIN50]

I have to ask.................

How does the puter know that EGR is missing (via PFE/DPFE feedback or some other mechanism)?

And what is the answer for the countless folks who have indeed removed the EGR and then saw part throttle pinging?

It's hard to disagree with what actually happens on these cars. Being a hands on kind of guy, I tailor things around what happens, not what should happen (Jason, I still stand behind the TPS adjusting stuff, for instance, as much as a certain someone wants to disagree ).

I'm certainly not disagreeing with you, and I applaud you posting the info (you have the patience and interest to read crap that I dont care enough to, and I appreciate it!). I just wanted to ask a couple questions about this..........

 

[TENGRAM]

I have to ask.................

How does the puter know that EGR is missing (via PFE/DPFE feedback or some other mechanism)?

And what is the answer for the countless folks who have indeed removed the EGR and then saw part throttle pinging?

It's hard to disagree with what actually happens on these cars. Being a hands on kind of guy, I tailor things around what happens, not what should happen (Jason, I still stand behind the TPS adjusting stuff, for instance, as much as a certain someone wants to disagree ).

I'm certainly not disagreeing with you, and I applaud you posting the info (you have the patience and interest to read crap that I dont care enough to, and I appreciate it!). I just wanted to ask a couple questions about this..........

if any EGR code is present (possibly excluding CM codes ) the ECM "knows" that the EGR is missing/disabled. for those who have experienced part-throttle pinging, i would suspect that their tuning (timing) was on the verge of detonation before the EGR delete, or that there were other contributing factors. also, i believe that if you only block the egr port (on the lower) from the upper, and leave the rest hooked up, this could cause detonation, since the ECM still adds timing, but the EGR is not cooling combustion.

 

[emagdnim]

This is proof never believe everything you read on the internet. I remember big arguments about this and all the people saying dont take it off!!

 

[vristang]

(Jason, I still stand behind the TPS adjusting stuff, for instance, as much as a certain someone wants to disagree ).

That dude is a riot

JT - I appreciate you adding this to the topic. Hopefully we can get a better understanding what really happens, which would never happen if it was just me making a post.

I know what you are saying. In my case I may have been getting the ping due to oil deposits on the pistons, I can't be sure. Or it may have been that my timing had been advanced a little too far? This was before I started using those fancy timing lights, so I will never be able to adress that though.
Once I get the motor straightened out I will have make some datalogs to see how the car reacts with and without the egr.

Since most of us advance the timing, this should be considered as well.
Another variable that I still don't fully understand is the "Alternative Strategy" that the EEC switches to.

I am still trying to decipher this section of the GUFB, but it is slow due to the terminology and all the logic diagrams.

My understanding is that the computer will not use EGR fuel and timing compensation any time there is an EGR code.
I am not entirely sure what tirggers the EGR codes though.
Obviously, I still have some reading to do.

jason

 

[emagdnim]

I was also curious about what tells the computer the EGR is not working , unhooking the sensor would probably be the easiest way but this causes some peoples check engine lights to come on..(not mine). Perhaps the egr elim kits that fool the computer into thinking the EGR is there to eliminate the check engine light actually prevent the computer from correctly adapting?

 

[vristang]

The dude that informed me of how the EEC reacts to the EGR is Joel5.0.

Here is a link he provided me that explains it.
http://www.my5oh.com/forum/viewtopic.php?p=225

JT - He also made some comments on the TPS in this link as well.

 

[jrichker]

I know this from personal experimentation, that the TPS has a very definite effect on idle. Last week I swapped the TPS for a spare I had laying round. Before the swap I had no idle surge and the engine would pull smoothly at 1500 RPM in 3'rd gear. I swapped the TPS, made several attempts to play with the adjustment, but still have the surge. Since the TPS was the only thing changed, it is the suspect component.

In like manner, my car has a cruse level ping that does not get worse, and in fact, disappears when you floor the accelerator. If it were an ignition timing issue, flooring the accelerator would make the pinging worse. I believe the EGR working at a sub standard level is the cause of this ping. I get an occasional code 34, EGR above closed limit & CEL. I have spent over 2 years and many $$$ on parts, replacing this and that to try and eliminate the ping. The this & that includes a new EGR valve ($95 - Ouch!) & EGR sensor. I have even removed the heads and wire brushed all the carbon out of the combustion chambers in an attempt to eliminate the ping without any results. I am reasonably convinced that an EGR that the computer thinks is functional, but really is working poorly will cause cruse level ping problems.

 

[HISSIN50]

This is kinda interesting. I've never considered deleting the EGR so I cant comment on that further (I don't even see mention of the feedback system for the EGR). But if an EGR code is present, the puter will supposedly bypass EGR function and EGR-specific trim (if I read things correctly). But then the resistor-trick takes care of the CEL. So is it safe to say that the CEL and EGR function in the computer dont keep tabs on eachother? The EGR can be made to 'be broken' and the CEL is tricked into not illuminating, but the puter doesnt pick up on the inconsistancy?

That was an interesting link. I respect Joel's thoughts (and he's respectful in posts that I've interacted with him on - he presents a mutual-respect kind of rapport with others on threads). I dont care who is posting about what, I think that's paramount to quality discussions.

I, like Joe, have had 'untextbook' experiences with fix-it issues. I think my mindset would be to maybe know/remember how it should work, but keeping in mind that it might not happen like it does in theory (for whatever reason), and be able to react to that accordlingly. That's a pretty safe way to think about it, it seems.

I'll be eager to hear more about all this stuff, in theory and in practice (funny coming from a guy who could care less about deleting an EGR - I have strict Emissions testing here).

Good thread.

 

[VG30DE]

I almost said something last time you said it, but I had nothing to back it up.
VG30DE, just curious, but you still have exhaust gas up to the spacer, the valve is just not opening, correct?

Thats correct. Everything is still in place and could be operational if I ever wanted to. ( no I never want it to work ever ) I have disconnected and removed the vacuum soleniod but still have the EGR position sensor connected, so the PCM knows that its not working, and thankfully I do not get a CEL with the position sensor still connected. It comes right on if I unplug it. So I get all the benefits of not having exhaust flow through the lower and upper manifolds, without any adverse conditions or the CEL. And I have friggen twin turbo. No chip, stock A3M. Runs mint.

 

[TENGRAM]

I know this from personal experimentation, that the TPS has a very definite effect on idle. Last week I swapped the TPS for a spare I had laying round. Before the swap I had no idle surge and the engine would pull smoothly at 1500 RPM in 3'rd gear. I swapped the TPS, made several attempts to play with the adjustment, but still have the surge. Since the TPS was the only thing changed, it is the suspect component.

like you said, the adjustment made no difference, only switching to a different sensor did. maybe the spare sensor was slow to react or had some other problem, while still measuring within spec?

In like manner, my car has a cruse level ping that does not get worse, and in fact, disappears when you floor the accelerator. If it were an ignition timing issue, flooring the accelerator would make the pinging worse. I believe the EGR working at a sub standard level is the cause of this ping. I get an occasional code 34, EGR above closed limit & CEL. I have spent over 2 years and many $$$ on parts, replacing this and that to try and eliminate the ping. The this & that includes a new EGR valve ($95 - Ouch!) & EGR sensor. I have even removed the heads and wire brushed all the carbon out of the combustion chambers in an attempt to eliminate the ping without any results.

if the 34 was a CM code, then i dont think the EGR related fuel and timing adjustments are bypassed. also, its odd that it is reading above closed limit (open). there are 2 kinds of egr sensors: black or white. did you get the right replacement? i'm sure you cleaned out the egr ports (in case the valve was unable to close enough), right?
i know you know your stuff, but you might check out Joel's EGR Troubleshooting Thread (you'll have to register to see that one), just in case you missed something.

I am reasonably convinced that an EGR that the computer thinks is functional, but really is working poorly will cause cruse level ping problems.

exactly

 

[stang&2Birds]

About the EGR:

Hmm, I never saw your posts saying that about the EGR, or I ignored them.

That information has been around since 1985 (when the 1986 Stangs came out). I have many Ford dealer service documents for the Stang and EEC-IV. They cover the years from 83 to 95. Plus, the dealer CDs, DVDs, Alldata Ford CDs, a *ton* of Dealer and other books, and so on. EBAY RULES!

 

[TENGRAM]

This is kinda interesting. I've never considered deleting the EGR so I cant comment on that further (I don't even see mention of the feedback system for the EGR). But if an EGR code is present, the puter will supposedly bypass EGR function and EGR-specific trim (if I read things correctly). But then the resistor-trick takes care of the CEL. So is it safe to say that the CEL and EGR function in the computer dont keep tabs on eachother? The EGR can be made to 'be broken' and the CEL is tricked into not illuminating, but the puter doesnt pick up on the inconsistancy?

That was an interesting link. I respect Joel's thoughts (and he's respectful in posts that I've interacted with him on - he presents a mutual-respect kind of rapport with others on threads). I dont care who is posting about what, I think that's paramount to quality discussions.

I, like Joe, have had 'untextbook' experiences with fix-it issues. I think my mindset would be to maybe know/remember how it should work, but keeping in mind that it might not happen like it does in theory (for whatever reason), and be able to react to that accordlingly. That's a pretty safe way to think about it, it seems.

I'll be eager to hear more about all this stuff, in theory and in practice (funny coming from a guy who could care less about deleting an EGR - I have strict Emissions testing here).

Good thread.

as i understand it, the resistor tells the ECM that the EGR is closed, so it does not use the EGR fuel/timing. but, then how does it avoid a "valve opening not detected" code 33? maybe it doesn't. with the vacuum line dettatched from my egr valve i have a KOER 33...but no CEL. yep, according to Joel's data, a lit CEL is caused by a 34 as well as 31 and 32...but not 33. so, if you delete the egr and you have a 31,32, or 34 as a result (depending on how much of it you delete), you could use the resistor to get a 33 which will not cause your CEL to illuminate...i think. hopefully someone w/ a resistor will jump in here and confirm my suspicions about the 33 being present with it installed.

IMHO, the problem with theories is that typically there are too many unknown variables, however, the same could be said for basing things on previous experience. nothing is ever exactly the same twice...profound, i know

 

[stang&2Birds]

Post Deleted:

Added nothing to the thread.
No techcnical information
No data
No theory


Daggs

 

[jrichker]

Daggar was right about you...

The first rule from my over 40 years of troubleshooting experience with complex systems ranging from automobles to airplanes to electronics and computers: the last thing that was done that changed the problem symptoms and made them worst is the primary suspect for the problem at hand.

It is my intention to put the old TPS back on, and when I do, I also expect the current idle quality problem to go away. While the TPS values are within limits to keep from setting a code, they are evidently not optimum for idle or smooth performance at very low speeds.