No fuel leaks that are apparent......if so there would be some indication with fuel puddling , dripping and fuel odor as well....none. New air and fuel filters are in place. Really haven't given the odometer much thought...............have been checking fuel mileage with the trip odometer and resetting at fill up. Need to check the trip odometer correlation to the actual odometer and against a known route, as well as one of my other vehicles, to see if anything is out of order with the odometer..........will post findings.

There's just no way you're burning that kind of fuel without a problem. When my engine started dropping mileage it turned out to be the ignition coil and you could smell the poor performance in the exhaust as it ran rich due to weak ignition spark. Your spark plug gap is correct I'm assuming since you installed new plugs.

If your rpm relative to speed checks out you should try filling up the tank and driving a known distance and topping it off once you get there for a good reference of what your getting per gallon. If you still find fuel economy to be that poor I'd be looking at engine compression at this point.

joseph,

Thanks for your insight and experiences. When I'm under the hood today chasing this thing, I will check / test the coil with a multimeter and see if there is any thing that comes up there. In some of your previous posts you suggested looking at the ignition control module (ICM) connections......intend to do that today. I'm thinking that the ICM not only provides spark to the plugs, but does also signal the ECM to advance the timing..........correct? Past experience says that if the ICM is dead, it's dead.the car won't fire..............not the case here. Is it possible that it's functioning OK in normal run mode, but not signaling the advance message to the ECM?

quote Originally posted by damccord: joseph, Thanks for your insight and experiences. When I'm under the hood today chasing this thing, I will check / test the coil with a multimeter and see if there is any thing that comes up there. In some of your previous posts you suggested looking at the ignition control module (ICM) connections......intend to do that today. I'm thinking that the ICM not only provides spark to the plugs, but does also signal the ECM to advance the timing..........correct? Past experience says that if the ICM is dead, it's dead.the car won't fire..............not the case here. Is it possible that it's functioning OK in normal run mode, but not signaling the advance message to the ECM?

Anything is possible. I know except in an emergency I will never install an Autozone module in any of my cars based solely on my experience with 3 of theirs. I distinctly remember replacing one with a genuine GM module and noticing wheel spin on launch where I didn't have it before without having made any adjustments to timing. The first went bad on install, the second after about 3 months of use and the car did run with it although when it malfunctioned it caused a considerable driveablility problem.

The same for their brand ignition coil. I don't have a lot of confidence in trying to detect a bad coil with a multimeter, but when my car started loosing power, smelling of fumes and getting the kind of mileage with a 4 speed that you're getting with no overdrive, I cranked the car up one night and looked in the engine bay in the dark and saw several arc points between the coil casing and the metal frame. You can see a white residue in day light at the points where this kind of phenomena is taking place. The spark to the plugs was too weak to ignite the mixture properly. It was at that time I realized the headaches I was having after my 30 mile commute were the result of CO from the exhaust. I couldn't smell it until it got bad enough.

Not aware of where you purchased your parts, just warning you to be careful with the brand of choice for parts that can deadline the car in an instant. I buy parts from Autozone, just not ignition unless it's name brand.

Ok.......Did some more work chasing it today . Here are the results. Cleaned up and unplugged/replugged ICM connectors multiple times. Checked the ignition coil per manual instructions with my multimeter (as posted on this site).....all checked out OK. Did clean up coil connections and its ground. Drove a known route to check the odometer and trip odometer, both are in line with each other and pretty accurate (within a couple tenths of my truck driving the same route). Put 2 oz. of acetone into a full tank of fuel.......to "clean up" any varnish, dirt, build up on the injectors. Drove the car 65 miles.......in town driving, at 25-40 mph. Re filled and checked mileage........17.6 mpg! When I refilled the tank, I put a can of Blaster Injector cleaner in it. Drove the car again in and around town ........35 miles, again in town traffic driving @ 25-40.....not babying it either. Refilled tank checked mileage..........18.4 mpg! Now that is more like what I would expect to be getting in town! Not sure what "fix" done today addressed the poor mileage being obtained previously or if it was a combination of these things...........but I'll take it. Will continue to monitor the fuel mileage and hope that today's efforts/results continue.

85SE Pretty much stone stock with 260K on the clock. It is fairly consistant at 25 mpg in the commute lane. On weekends with no one in front of me it is around 20.

https://www.fiero.nl/forum/icons/icon14.gif

Just click edit on my post to see how I changed yours to show what you wanted to show.

Charlie

[This message has been edited by cptsnoopy (edited 12-16-2010).]

quote Originally posted by damccord: OK, I just filled the car up and checked the mileage..................10.7 (83.5 miles / 7.8 gallons) !.....REALLY. This is starting to get old and frustrating If you read my original posts in the thread I've done all the things that you would associate with poor fuel mileage. Plugs, wires, cap, rotor, check for vacuum leaks, IAC, O2 Sensor, EGR Valve, Ignition timing, The car runs absolutely fine. I'm out of ideas here........only thing I've got left is Catalytic Converter being plugged/restricted, but would expect that I would have some indications in how the car runs and would be significantly down on power.........am I right in my thought process here? Guess I'll try and advance the timing as far as possible without getting detonation, run some fuel system/injector cleaner with a couple tanks of fuel..............maybe injectors are dirty/varnished and not cimpletely shutting of, resulting in leaking down excessive fuel. Would think that there would be some indication of this in the car running noticeably rich or loading up.....or would the ECM be able to adjust around this and mask it? Another thought that came to mind..................did someone prior to me buying the car put a chip in it and would that deliver the horrible mileage I'm getting? Anyone with experience with running chips able to weigh in? Guess I need to pull the console and check the prom that is installed in the ECM. At my wit's end with chasing this. Any advice,input, help would be welcomed and appreciated!

Okay...my next two cents worth: As I said in my other reply, I've done all those things you did and more. The one thing I didn't mention is I removed my EGR, and replaced my cat with a straight pipe. It did make the mileage go up, but just a little (maybe a mile..which helps) but my car always got fairly good mileage, and after doing all those things, like you did, it helped a little, but it's always done much better than yours. Mostly it made it sound allot better!

Have you ever heard of a lemon engine? Production cars are turned out of the factory at break-neck speed to make money. We customers just have to gamble that the engine (as well as all other parts) went together good. The engine's performance is highly dependent on how well balanced it came out. Some engines are unbelievably good, while others are lemons, or way out of balance. If the crank is off just a little, that throws the whole engine out. Try running Royal Purple oil with a K&N or Royal Purple filter. 15-40 if you use any significant amount of oil, or 10-30 if you use very little oil. This act alone caused both mine and my son's cars to increase mileage more than any thing. It's worth a try. Dyno tests made on brand-new small block Ford bronco's, before and after Royal Purple switch, made 7% horsepower increase (as I recall) . You can see it on youtube. Friction tests done at testing laboratories, showed huge reduction of friction vs high performance petrolium oils. They even showed how an old engine with bearing wear, actually repaired the bearing surfaces to a degree.

Royal Purple is the synthetic oil is the formula developed by Russia to run their trucks in Siberia....as I understand. It made my son's 210K mile '85 GT run like it was new, driving 80 mph to and from a round trip of over 400 miles +- . It got better mileage than ever, and didn't use a drop of oil doing it. It started using a little oil driving around town, after we got back, but his mileage in town was right around 24-25 mpg. Before Royal Purple it was around 21-23 mpg. By-the-way, my '86 GT with Getrag 5-spd. is getting about 21-22 in town now, but I know I've got other issues, because I was getting 23-25 around town before and 32-34 on the highway, depending if it was straight, climbing or down-hill trip. I'm actually running GTX 10-30 with 1-qt. of Royal Purple as an additive. When I change oil to all Royal Purple, I expect a jump, and hope for 25 around town and 35 on the highway. I've also got bigger drive tires with my new Falken 225/60/15's , which replaced my old 205's I had in the rear. That's about an inch or more increase in diameter, which will make a difference in mileage too (going the same distance with the less rpm's). Hope this helps...

One more thing...porting! Porting always helps horsepower and mileage, but, the 2.8 V-6 has bad breathing issues, due to the square holes punched in each exhaust header pipe-connection, instead of porting (or even punching-out) a round hole to match the pipe diameter (manufacturing issue again). If you ever have any of the headers off for any reason, be sure to port them for a big power/mileage increase. The small engine size and low compression doesn't warrant expensive headers. It's kind of like running high octane case when the engine isn't designed for it...it actually hinders efficiency.

Speaking of high octane, If you don't have the compression to burn-off the fuel in each explosion, it tends to burn continuously, as I understand it. I had a Chevy Chaparral 400 hp hypo327 that had 12:1 compression ratio, which ran best on the high octane fuel from the local airport. The engine combustion chamber and entire exhaust system left a white burn residue. If I drove it like a normal car, I had to change the AC44 plugs once a week. It was designed for racing, not for commuting. That was just the opposite of running a low compression engine...that uses low octane gas. For what it's worth...?

[This message has been edited by hypo327 (edited 12-16-2010).]

You gained some improvement with injector cleaning. While doing some research to explore the possibility of using E85 compatible fuel injection components for water meth injection I discovered some emphasis on info I was already aware of but took for granted. Fuel atomization. Note that GM OBDII vehicles and up run static fuel pressures in excess of 55 psi compared to the Fieros' ~40. I viewed some spray patterns on Youtube and read some documentation that was so clear in its theory and demonstration that I intend to bump my static fuel pressure up to 60 psi (my injectors are rated as high as 80 psi). If you are running the old pentle style injectors your spray pattern will look like a stream instead of a mist. It was stated that atomized fuel is most beneficial at cruise speed when cylinder filling is slowest and in most need of atomized fuel.

Look for more up to date fuel injectors or newer and that will probably improve your fuel economy even more.

Here's a demo of a later style injector, the old pintle injectors spray a stream more so than a mist.

http://www.youtube.com/watch?v=KgL1WFfRzis