: Sensor check

07-08-06, 05:47 PM
Iīm still fighting with my poor mileage, now I decided to check all engine sensors, but how to do it thoroughly - sometime I unplug or clean something randomly, now itīs time for deep systematic check.

How can I check all sensors, what is the data output, how to wire it?

I mean, some sensor must be wrong on this car (ī96 FWB), because the mileage is now nearly 2 times lower as all other Fleetwoods I ever had, and - interesting - it decreases more and more. I changed all what to change was (even the four O2 sensors and catalytic converters), I passed very successfully the voluntary emission inspection to see if I run not rich or lean, but with every 1000 miles the mileage goes down by 1 MPG... Thatīs fact, and because it is not usual, it must be reparable.

Maybe, the computer is wrong, is that possible? How to check him? No Check Engine light, no codes by reading the OBD... Tune him, can it help?

BTW, the car has 80.000 driven miles, only one previous owner, seems the grandpa never drove someone other as himself, garage keept, with all maintenance, no rust, no leaks, looks really like new, drives great, an eyecatcher:

07-08-06, 11:45 PM
Is the car RPO V4P? Look at the SPID, the Service Parts Identification tag in the trunk on the underside of the lid. Look for V4P, that is the tow package, not good for mileage if you have it. Look for the gearing, would be a Gxx code. This can give you some clue on what mileage should be.

If the car passes emissions, likely the O2's are fine. People love to change them and waste a lot of $$ on them.

Obvious things:
Engine Oil, is it clean and kept fresh? I prefer 15W40 Rotella T/Delo 400/Delvac 1300. I will NOT run anything else. Search this board and the HT4100/4.5/4.9L forums for more info. Synthetic is another word to look for, but be prepared! If you are gonna keep it for a long time, stick with 15W40. If not and you don't care, 5W30 is fine. But remember! 5W30 oils on the shelf today do NOT meet the engine oil specs that is specified for your car!!! The 15W40 oils still do. For now.... The oil specs are NOT backwards compatible like they are interpreted to be.

Tune up, plugs, wires, Opti, air filter.

Dirty MAF, don't mess with it if you aren't sure what you are doing, it can be easily damaged. So be careful with it.

Tire pressure, 35 psi is best overall, a little firm, but best for economy without damaging tire wear


Heavy foot? You aren't taking on them pesky Hemi Ram's are you? It is fun to keep beating them, but it hurts the gas mileage....

Driving with windows open can hurt mileage, AC on and windows up may help. I average 18.5-19 with AC on in my 62 mile each way commute to work and back. No cruise right now and I still am pushing high 18's all the time.

Fresh trans fluid?

Use AC Delco air filter. Don't waste $$ on crap like Frams. They are restrictive and hurt mpgs...

Brakes dragging? I had a bad lining on a new brake shoe that would drag at times. Really put the damper on mileage. Was a bugger to troubleshoot.

Looks good! Astroroof and all!!!

07-09-06, 02:28 AM
I'll leave the troubleshooting to the gurus on this board, but had to mention to you that's one beautiful looking FWB you have there! It looks to be in top shape, cosmetically.

Well done!

07-09-06, 08:37 PM
Limo, First things first, fabulous car!

Did I miss it, what mileage are you actually getting? How do you check it? If mileage drops with every 1000 miles driven, I assume it will aventually approach 0 MPG...then you can sell your gas hog car to me. :histeric: Just a little humor there.

Seriously, it must level out ...eventually, or more likely fluctuate with road, traffic, driving style, etc. Are you checking mileage under the same conditions, or as closely as your can, e.g.,type of roads, same drive styles, etc. If not, you are getting a rough overall average, at best. You must compare "apples to apples" to expect to get similar results. I can tell you are frustrated, especially after installing the parts.

My mileage can vary as much as 5-6MPG if I don't watch my gas pedal, or drive in a lot of city traffic.

07-10-06, 04:10 PM
Actually Iīm on 13.5 city and 15.5 highway. I started my exact measuring as I drove 15.2 in the city. The conditions are similar, no heavy foot (my "old" ī94 FWD did 24.5 / 17 on the same road). The gearing code on SPID is GW9 (2.93 ratio).

OK, I try to change (or cross-change from another FWB that works) the sensors.

As I bought this car, all brakes, discs + air filter was new, chasis lubricated, no scratches even on the anticorosive protection....

I changed the fuel filter, spark plugs + wires, tires, oil 5W-30 + filter. EGR cleaned, Idle Air Control valve checked, Throttle Position Sensor checked, Fuel Pressure checked, PCV valve checked, EVAP canister lines too, all vacuums lines hold the vacuum, yesterday I cleaned the MAF sensor, engine temp sensor works well, I replaced the intake air temperature sensor...

Now the trans is waiting for personal attention.

Well, if itīs not a bug on some sensor or what, I accept the mileage, but I drove two ī88 Brougham RWD with the famous 307 Olds engine, I drove two Fleetwoods (ī94 FWD & ī95 FWD) , I drove the cars the under same road conditions, and the mileage was a dream... and just this beauty one is gas hungry.

07-10-06, 09:49 PM
I understand your frustration. Sounds like you have the experience with the FTWD to know what you "should" be getting.
Your 13.5 city mileage is what I get towing on the road or with a heavy foot in city stop-and-go driving with my V4P '94 FTWD (3.42 gearing). 15 to 17MPG is a more normal range for me in the "city", and 19 to 20+MPG for highway.

Could you post your Emissions test data, so we can compare; however, I think yours would have to show a very rich indication to be able to influence gas mileage to the extent you are experiencing.

I feel you should be getting a little better and consistent mileage too, but not sure what else you could check. EGR came to mind, but you have cleaned that. In all your recent work, have you reset your computer unit with a complete power disconnect? If not, maybe with all the connecting and disconnecting of individual modules, the system calibration got out of whack. I know that may sound off the wall, but my knowledge of electronic system component interaction is weak.

Besides the items Nodih provided, you could also search for mileage posting within the FTWD and LT1 forums. I'm sure other mileage issues have been asked and discussed.

Good luck.

07-13-06, 12:14 PM
I found what. Seems I drive wihtout the PCM... Seems not possible. I start new thread.