EGR /SEFI Theory of Operation and it's Evolution

[DPDISXR4Ti]

This topic came up in a different thread, but it's worthy of it's own discussion, in it's own thread. It's interesting that the early 4.0 implementations, both the Ranger and Explorer (and I presume Aerostar as well), did not have EGR at all. Certainly the technology existed and was put into production on other platforms in the early 80's. I can only assume that the initial 4.0 calibrations were clean enough to pass the EPA guidelines without EGR, so Ford opted to keep things simple and left it off.

Starting in 1993 (possibly earlier for CA vehicles?), EGR got phased in, first on the Explorer and then in 1994 on the Ranger. I'm still trying to figure this out, but it would seem that it's implementation was a little more complex than the earlier 80's EGR implementations. Sequential Fuel Injection (SEFI) arrived on the scene at the same time as EGR, and SEFI required a Cam Position Sensor. From what I've observed, you got all (EGR, SEFI, Cam Sensor) or none on the 4.0. Does one require the other? I don't believe so, but I'm willing to be convinced otherwise.

Part of why I'm raising this topic is to determine the cross-compatibility of early EEC-IV 4.0 PCM's with later ones. Certainly they are NOT plug-n-play compatible, as the wiring did change. But let's say you wanted to convert your 1991 Ranger 4.0 from EFI to SEFI. Could that be done by simply moving a couple wires, adding the additional circuits for each of the fuel injectors and swapping out the "dumb" oil pump drive with a later one that has the Cam Sensor?

 

[gaz]

Here is the text from the document, FORD FUEL INJECTION & ELECTRONIC ENGINE CONTROL by Charles O. Probst, SAE.

The first 2 pics support that SFI was available in 92 but only with the 3.0l and that starting in 1993, the OHV 4.0l came in SFI (with EGR, the California emissions version) or MFI (no EGR, Federal version).

The following 3 pics with associated text explain the general function but do not clarify precisely what the PCM does with it or exactly why.

The forum member I would solicit is @RonD .

 

[alwaysFlOoReD]

Here is the text from the document, FORD FUEL INJECTION & ELECTRONIC ENGINE CONTROL by Charles O. Probst, SAE.

The first 2 pics support that SFE was available in 92 but only with the 3.0l and that starting in 1993, the OHV 4.0l came in SFI (with EGR, the California emissy version) or MFI (no EGR, Federal version).

The following 3 pics with associated text explain the general function but do not clarify precisely what the PCM does with it or exactly why.

The forum member I would sollicit is @RonD .

View attachment 121665View attachment 121666

Yes, RonD is a wealth of info. Unfortunately he has told me he will no longer be on any forums. He will be missed.

 

[rubydist]

Another factor in this was that the emissions standards kept getting more stringent, so the manufacturers were required to keep adding complexity to meet those standards.

The engine wiring for sefi is much different from efi, that much I know for a fact, because I did consider swapping an early 90s F150 to sefi, but decided it was not worth the effort due to all the wiring differences.

 

[DPDISXR4Ti]

Another factor in this was that the emissions standards kept getting more stringent, so the manufacturers were required to keep adding complexity to meet those standards.

The engine wiring for sefi is much different from efi, that much I know for a fact, because I did consider swapping an early 90s F150 to sefi, but decided it was not worth the effort due to all the wiring differences.

No doubt, as the emissions standards got more strict, the emissions-reducing technology got more sophisticated. I'm sure that's what caused the development of DPFE as a more sophisticated version of PFE. I'm still somewhat surprised that the early 4.0 OHV engines had neither version of EGR, and just jumped right in with DPFE in 1994 (on the Ranger).

I have the schematics here for the EFI and SEFI engines, and they're not that different. It's just a matter of adding some wires for each of the injectors (rather than batch-fire), and moving a couple others around. In theory, you'd also need to switch from a single O2 sensor to one on each side. I think however that you could just feed the single existing O2 output to both circuits and the PCM wouldn't be the wiser. Maybe come back another day and plumb in a O2 bung on each side if you really wanted to.

The thing I would NOT want to do however is add in EGR. I hate all the pipes, vacuum lines, and wires that EGR adds. I want simple engine bays that are easy to work on. I've deleted EGR on PFE vehicles with little consequence. If the timing map is tight, you might need to retard it a couple degrees, but usually that's not the case. But what happens when you delete EGR on a DPFE engine? Keep in mind, the basic goal is to be able to run a factory PCM without any sort of tune.

 

[rubydist]

I have the SCT unlock codes for both my 03 manual (no egr) and my 09 automatic (with egr) and the factory tunes are miles apart on those 2 - the base timing is completely different.

 

[gaz]

@DPDISXR4Ti
The 93-94 SFI 4.0l set ups were rated a 10% higher fuel economy than the Federal version. Despite all the PITA issues the EGR system adds to the engine bay, I'll take +10% fuel economy EVERYDAY OF THE WEEK + Sunday; afterall, i only need to pop a valve cover every 35k miles or so to adjust the valve train to maintain optimum efficency.

Both of my 2.9l's had an EGR system and i HATED having to work around those rigid, ALWAYS right where i needed my hand to be. On the other hand, pulling 28+ mpg on 32" rubber with 5" of lift with a FULL load, driving through some of our great nation's mountain passes told me to leave it alone ..)

This thread has motivated me to join you to learn whether or why, the EGR is an improvement and why it's worth maintaining. One thing for certain, both the fitting that hold the EGR tubing onto the exhaust manifold and everything bolted to the intake manifold, are far worse to disassemble than any muffler or exhaust pipe hardware.

You are ABSOLUTELY correct about needing two O² sensors; if it didn't cost more, add weight and present engineer challenges, i believe Ford would have come from the factory with cross flow dual exhaust systems; the the earlier 2.9l exhaust manifold "H" pipe says it out loud ..)

@rubydist
Now this timing ∆ is some interesting info!!

 

[rubydist]

I don't know how much of it is auto v. manual, or egr v. no egr, or 6 years later tighter emissions specs but it is way more different than I expected.

 

[DPDISXR4Ti]

@DPDISXR4Ti
The 93-94 SFI 4.0l set ups were rated a 10% higher fuel economy than the Federal version.

Do you have some sort of reference for this? I'm looking at the EPA site right now and it's indicating identical fuel mileage between a '92 4.0 (no EGR) and a '94 4.0 Ranger (EGR). '95 Ranger 4.0 indicates a 5.7% improvement (5.6 gal/mi vs. 5.3), but I suspect the higher compression and faster-burn head that appeared in 1995 accounts for most all of that.

 

[gaz]

The 1995 does have the fast burn heads but the compression ratio stayed the same from 1991-1996. Ford accomplished this by increasing the dish in the piston to maintain 9:1.

I am searching for where I saved the fuel.econmy numbers.

 

[DPDISXR4Ti]

I have the SCT unlock codes for both my 03 manual (no egr) and my 09 automatic (with egr) and the factory tunes are miles apart on those 2 - the base timing is completely different.

Did you mean '93 rather than '03? The '09 would be the OHC engine, so I would expect that to be different from the OHV timing map. Or are you comparing ignition maps of the '03 OHC to the '09 OHC?

 

[rubydist]

No, they were all SOHC beginning in 2001, so both the 03 and 09 are SOHC.

 

[DPDISXR4Ti]

No, they were all SOHC beginning in 2001, so both the 03 and 09 are SOHC.

Okay, got it. As you indicate, there's a lot going on there with all the differences, so it's hard to draw any definitive conclusions.