2.3L ('83-'97) Drilling & tapping '94 intake plenum for EGR?

[lowspeedpursuit]

Most EGR threads are from people who want to remove it, which then devolve into arguments between people who think the system "robs power" and people who think it's important. I have the opposite problem.

I drive an auto-to-manual swapped '94. In the '94 2.3L trucks, EGR is determined entirely by transmission, not Cali. emissions. All manuals had EGR, and all automatics did not. The truck technically still ran on the auto computer, but not great. The manual swap computer expects EGR, and is throwing codes, and I believe putting me into base timing mode. I don't really care about the CEL, but I do care that I'm suddenly getting 15mpg instead of 24.

The easiest way to fix this seems to be to add EGR to my truck. Exhaust manifold already has the port. I have the entire trans. donor truck, which means the pipe, DPFE, valve, solenoid, and wiring. But, the donor is '95, which uses a newer intake manifold. I can't swap manifolds because the '94 head has what appears to be a coolant passage that the '95 manifold would leave uncovered. The plenums, where the EGR valve needs to go, are matched to the manifolds.

Is it remotely possible to modify a non-EGR plenum to accept the EGR valve? There doesn't seem to be a great wide/flat surface anywhere, except maybe the ford logo. The EGR plenums are a totally different casting, with a whole extra bit coming off the back near the throttle body that ends in a flat surface for the EGR valve. I feel like I've seen someone talk about doing it, but never give details or confirm their success, and I'm having trouble finding that thread again.

Thanks!

 

[Shran]

What about finding a different '94 donor that came with EGR from the factory? And exactly what computer are you using? I have heard of people using a resistor on the EGR solenoid plug when they block the EGR port off to fool the computer into thinking the EGR is there but I dunno if that would apply to your situation. Maybe easier than actually adding all that junk?

Using parts of the harness from the '95 and the EGR parts seems like a huge can of worms to open in my mind. I guess it seems easier to me to find a '94 or older donor that will be plug and play with your '94...

Also kind of curious why the auto computer didn't work. I used a '94 auto ECM on a 4.0/manual swap and it ran great apart from throwing codes for trans shift solenoids that were obviously not there. Had issues with it after some engine work was done and it had to be tuned to run the way it should.

 

[lowspeedpursuit]

Pulling a '93/'94 (maybe earlier as well?) EGR plenum is definitely a possibility, subject to pricing (not great on ebay) and availability (zero at junkyards w/i an hour or so). This is partly me exploring the free/convenient option before trying to chase one down.

I can weld steel, so the tube is effectively "adjustable", and the electronics match across the '94/'95 facelift acording to the catalog.

The auto computer "worked" in that it ran and drove. The main issue was that it didn't idle right. I think it has something to do with the torque converter and jumping the park/neutral switch, but tuning is basically wizardry to me. Changing nothing about the throttle, after the transmission swap, the idle would jump around and sometimes threaten to stall. The problem was even worse if I was running the A/C. In order to get it to stabilize, I had to turn the throttle stop up stupidly high. IAC works, no vacuum leaks, etc. All other things being equal, the truck idled normally before the trans swap and then normally again after the computer swap. I'm also not sure if the auto computer would respect the signal from the clutch switch, whatever that's used for (rev hang?). Interestingly, my auto computer also didn't care about the auto trans. being unplugged; I thought getting a CEL for that was a '95+ thing.

On bypassing the DPFE / solenoid, my understanding from reading about EGR is that because the recirculated exhaust isn't remotely as combustible as gasoline, EGR lowers cylinder temps. So, if you trick the computer into thinking the EGR is working and advancing the timing, but you're not actually putting the exhaust in, you'll get higher temps. and eventually detonation. On newer motors, I guess you could let the knock sensor catch it and drop back to base timing when it happens, but my motor doesn't have one. Whether the EGR bypass -> detonation problem is overblown, or whether something can be done about it (colder plugs?) is something I'm also curious about.

 

[Shran]

The only thing I did was wire the auto trans park/neutral switch wiring into the neutral position switch on the manual transmission and that was only done so that the truck would start.

I was under the impression that the "rev hang" or whatever the technical term is for it, is determined by the speed sensor in the trans or t-case, and maybe an input from the clutch switch as well? So basically if the vehicle is moving, clutch pedal pushed in, it keeps the engine RPM higher and then drops it down to normal idle a second or two after the vehicle comes to a stop. I'm not sure how to make that happen with an auto computer; in my case, with my swap, it just did it anyway without ANY of the clutch switch wiring in place (I used a dash harness from an auto trans Explorer so it wasn't there at all.) The idle would stay high until the truck came to a stop. That led me to believe that it was relying only on input from the speed sensor to make that happen. But, that was a 4.0 swap, different animal than you are dealing with.

Your comment about moving the throttle stop was interesting. I wonder if instead of doing that, you could enlarge the throttle position sensor slots to make it adjustable if it's not already and then turn it to increase the voltage at idle but not open the throttle butterfly like you did with the stop screw. Auto and manual trucks have different idle speeds set at the factory so I wonder if that would help compensate.

 

[lowspeedpursuit]

Honestly, I could have lived without whatever adjustments the clutch switch is supposed to bring to the table; I also just left the clutch switch jumper in place until I swapped the computers. But, the super high idle was killing me.

I have basically no experience with electrical signals, but "tricking" the TPS is an interesting idea. Since I'm willing to give up the clutch switch, I could probably live with the auto computer and an alternate method of fixing the idle. That said, I tried to take it off yesterday and my TPS screws are seized to the throttle body, so maybe that's a project for when I have more time. I think the donor throttle body is in the back of the shop somewhere.

It would be a lot easier to understand how the idle is supposed to work if I had a better understanding of the computer's strategy, but I don't think there's historically been any interest in reverse-engineering the 2.3L computer. Everyone focuses on tuning the more powerful motors.

 

[Shran]

You might try a manual impact driver (the kind you attach a socket to and hit with a hammer) for those screws. They work well for small fasteners like that and there is less chance of stripping the head or breaking it as opposed to brute force with a different hand tool or power tools.

FWIW what you would be looking for are two of the wires that go to the TPS. I believe one is reference voltage (5v at all times) plus a ground and another wire that returns voltage to the ECM. The latter two are what you want to probe with a multimeter. Normally at idle with the throttle closed you want to see somewhere between 0.75-1v and as you slowly open the throttle you would see the voltage climb to somewhere close to 5v when the throttle is wide open. Many TPS are slotted so that you can rotate them slightly and adjust the idle voltage.

As far as tuning these goes - there is really very little difference between your truck and a fox body Mustang with a 302. Or any other Ford product made in the mid 80's up to '94. They are all OBD-1 systems and either function off mass air calculations or speed density. So in theory if you find someone who can tune a fox body car, the principle is the same, the hardware involved is more or less the same as well, they just need different numbers for spark timing, air/fuel ratios, etc. Finding that person can be difficult and really may not be worth your time if you can fix it a different way with factory parts.