Some intital results.....

After installing it I took a 150 mile highway drive to another town on the other side of the mountians (business trip). I had the IAT mod dial set to about the 3/4 mark ~ 7k on the potentiometer and 3k from the IAT. Same signal to the ECU as if it were only around -15 degrees outside.

Wish I had filled up the tank before starting out just to see what the mileage was. I had already driven about 60 miles around town before doing the install, which influenced the gas mileage. Got about 18.5 mpg in mixed driving. Not great, but only a little less than the previous average of around 19-20 mpg for mixed driving.

I decided to dial it down just a little. Set it to the 1/2 way point ~ 5k on the potentiometer and 3k from the IAT. Same signal to the ECU as if the outside temp were around 10 degrees. Filled it up for the return trip and filled it up again after I got back. I couldn't believe it, but it got 26.7 mpg! Of course about 140 of this 150 miles was straight highway driving, but it also included climbing TWO 4,000-5,000 foot mountain passes! 26.7 mpg is better mileage than it had EVER gotten since I bought it! Only about 2.3 mpg lower than the EPA highway estimate of 29 for the rig when it was brand new! Needless to say I'm VERY excited about this!

Edit: The 18 liter and 2.4 liter intake and throttle body gaskets came in today. The intakes are TOTALLY different (bummer) BUT the throttle body gaskets are identical (whoohoo!)

Soooo, looks like I need to locate one of the slightly larger throttle bodies for a 2.4 liter as my next mod to try and pump it up some more.....

 

You make me wish I was still stuck with my wife's little 90 eclipse 1.8. It sounds like you've come up with something applicable for lots of different vehicles with Natural aspiration. I'll forward this thread to a few guys who have similar needs.

 

HEY! Thanks for replying FireDoc! I was beginning to imagine that I heard an echo in here

I can't really take credit for "coming up with it". It was actually developed by someone else and eBay has a bunch of sellers offering several variations. They are usually advertised as "Up to 20 HP boost for your <insert make & model name here>" or something similar.

They range from under $10 for a 2-cent resistor and an instruction sheet on what wires to hook it up to, all the way up to a fully adjustable potentiometer in a small enclosure with install instructions for around $40-$50. I just built the more sophisticated and expensive version myself for about the price of the cheapo version.

I'm pretty excited about the improvement and am looking forward to further documenting the results and fine-tuning it to get the best performance/mpg balance. I drive quite a bit for my job, so I should be able to gather data pretty quickly. I'm even MORE excited about the possibility of the throttle body swap and what kind of gains that may produce.

Again, thanks for the encouraging reply and I'll continue to report results as I gather them.

 

I work 3 days on, 4 days off , so I only get to reply thurs thru sat. All other time is spent on the water pretty much. But I, and others are reading.

 

HMMMN, 3 days on and 4 days off and your handle is FireDoc, hmmmmn....

Wouldn't happen to be a fire department EMT, would you?

 

It depends on the day, We rotate if we are certified to do other jobs. Mainly I am an Engineer.

 

Engineer? As in holder of a BS in an engineering discipline? Or as in the guy in charge of a (fire) engine?

I'm a Computer Engineer and MCSE myself.

BTW, still not having much luck finding an adjustable cam gear. The only one I've found is made by RPW and the freight for the new gear from Australia, and to return mine to them as a core, is around 80 bucks! Add that to the $100 price tag and it starts looking a bit steep as an "experiment". Anybody got a line on any other cam gear that will work on the 4G93? The same engine was used in the 93-96 Mirage, but none of the big names seem to make one for it. I'm actually starting to think about picking up a junkyard cam gear and try making my own!

To that end I pulled the cam gear cover off to take some measurements and discovered something VERY interesting. Somebody made a mistake and installed the timing belt 1-notch off. The cam gear was already advanced too much! Since it is a 48-tooth gear, advancing the gear one tooth on the notched belt had the cam advanced 7.5 degrees (360 degrees / 48 teeth = 7.5 degrees per tooth). I corrected that and reset the timing and it is already running much better. Pulls MUCH stronger at low RPMs. I can get a smooth launch at around 1000 RPMs now.

I did a number of full throttle runs up that same 6% grade hill mentioned in my earlier post. I made slight timing adjustments between each run to get my base timing set to maximum advance for the best power and torque without pinging. Got it pretty much perfectly dialed in and it is running great. I can top that same hill in 4th gear at 55 mph whereas before it was 50 mph in 3rd.

Its still no low-end torque monster, but it is certainly much better. Apparently 7.5 degrees cam advance was TOO MUCH. I still want an adjustable cam gear to see how it does with about half that much advance - around 3, 4, or 5 degrees or so. I'll continue reporting how it goes as I make changes and adjustments.

 

BobC92, I just got back from being away 10 days for a cataract operation. Just want to let you know I read (can now see) and enjoyed your entire post. A good learning tool for me. I wish more posters here would be courteous enough to respond with the results of suggestions made to solve their problems. Seems most jump in as newbies, post once and are never heard from again. The people trying to help and learn hardly get any feedback. I hope you stay Bob.
I have a question. since you are fooling the computer into thinking the air temp is lower than actual, the air is actually less dense. Do you know if you are getting complete burning of the fuel mixture? It would be interesting to use an exhaust gas analyser with different pot. settings to see what your air/fuel ratio is like?? Have you looked at the plugs to see how they look? Rich mixture could be hard on cat?

 

All excellent questions, PC. Unfortunately I don't know the definative answers to most of them at this time! I did just check my plugs over the weekend and they looked fine - no soot or other signs of fuel loading.

I also know that the exhaust doesn't smell rich, for what that's worth. Also the mileage I've been getting supports it running lean enough. My supposition is that the "normal" air/fuel ratio is probably just slightly on the lean side of the "perfect" stoichiometric 14.7:1 air/fuel mixture - in the interest of maximizing fuel economy. When you think about it the difference in the density of air that is 65 degrees, and air that is 10 degrees below zero, it is really pretty small percentage-wise. I'm thinking that it is unlikely that the modifications I have made to the IAT result in an air/fuel ratio any richer than 13.5:1 or, more likely, 14:1.

Therefore, given all that, along with the condition of the plugs, no excess fuel odor in the exhaust, and good mpg I'm pretty confident that it isn't doing any damage. I'd sure like to take your suggestion and have the exhaust gas analyzer results to back that up though. I just don't know anyone who has one to use without paying them for the priviledge.

 

Progress report (sort of). I've created a spreadsheet to track my gas mileage. So far I'm averaging around 19 mpg in the city, and 27 on the freeway.

Seems like the thing that makes the most difference in mileage - maybe even more than city/highway or the setting of the IAT sensor adjuster is my use of the AC! In mixed driving I seem to get around 25 mpg with it off, but as low as 15 mpg with it on!

I spent $23 on eBay for an oiled gauze filter (K&N knockoff) and a MAF adapter to install it. I'm looking forward to seeing what kind of benefit I get out of it.

I took a gamble and bought a good, tested, used throttle body off a 92 Expo with the 2.4 liter engine. Found it at a wrecking yard in PA for $50 including shipping. It isn't much of a gamble because I'm about 90% sure it will fit. The big question is how will it work with the 1.8 liter's MAF. I found a 2.4 liter MAF locally for just a few bucks - just in case I need it.

At this point I'm planning on doing just one mod at a time - with a week or two to evaluate in between. That way I can see what gives the most bang for the buck. I'll keep reporting back - just for the heck of it.