Ok so before I tuned up my 88 GT with the 2.8l. I was getting say 23-24 mpg city and 32 highway. Now when I did the tune up I changed the oil to some Mobil 1 5w30 oil and a k&n oil filter. I also put in some bosch platinum two's and some STI spark plug wires off of the fiero store. I also changed the air filter because the previous air filter had rust in it. My valve cover closest to the back of the car is started leaking oil, so I think I will put new gaskets in the whole intake manifold and covers. Now my oil pressure is at about 30-33 psi when idling at 1100 rpms. Now I also pulled code 32 but I dont think that would be causing that bad of gas mileage from being restricted from vacumm at high speeds. So what I am asking is maybe I need to do the fuel filter and crankcase filter too? maybe I need a new EGR valve solenoid? EGR Valve? Lines? I have no idea. Or are some of the things in the tuneup giving me bad gas mileage? Thanks for the input guys.

You never said what your bad gas mileage is now.

How long since you changed your O2 sensor? It is a big player in gas mileage.

Here is a good discussion of the code 32.
https://www.fiero.nl/forum/Forum2/HTML/045528.html

[This message has been edited by Hudini (edited 09-25-2007).]

Oh sorry about that. Its getting like 13 to the gallon right now maybe less. I dont know how long its been since the 02 sensor has been replaced. I just got the car about a month or less ago. I think it also needs a new tps because the idle is erratic sometimes.

Ok, cool. Now you might get some BS calls about the 32 hwy mileage as the car was never rated that high even when brand new. Not saying you didn't get that mileage but it is rather unlikely without running dangerously lean.

An erratic idle can be caused by so many things. I would start with a thorough cleaning of the throttle body including the Idle Air Control passage and the IAC itself. It just unscrews from the throttle body. The little bullet shaped nose (pintle) gets gummed up and can cause problems. Some O2 sensor safe carb or TB cleaner will work wonders if it's just dirt causing the problems.

Here is a pic showing the IAC port and IAC itself. Shoot some cleaner all around inside.

yea thats what I was getting on the way home from grabbing the car. The motor is rebuilt but just started getting bad gas mileage. Thanks for the advice again hudini.

If you were getting the mileage you stated up until you worked on it, I would say it was something you did while working on it. I would not look for another problem just try to figure what went wrong. How does it run compared to before the tune up?
Later ...Harry...

Lots of posts out here about NEVER using Bosch Platinum plugs in a 2.8. They are prone to fail quickly. Use AC or NGK only. Ed

NEVER use platinum spark plugs unless you are running boost, higher compression or have a car that requires high octane fuel. My old camaro had 10:1 compression and ran nitrous and it burned through a set of platinum's in less than a week. I put good ole autolites or delco and they last forever with little to no fouling.

Lots of posts here about never using Mobil one oil in a flat tappet engine as well. something about the zinc levels are so low the cam will wear out in a hurry if you use synthetic.

I do know that synthetics run at a lower oil pressure so your drop is because of switching to a synthetic.

Firefighter is so correct!!5 speed V6 will get 32mpg if not driven fast,23,24 mpg in light tracffic,,serious drop has to related to your recent tuneup,how does engine run?? a 40% drop in milage would show up in bad performance you can feel,,is car running rich??if engine runs better than before install of plugs could be leak,often if filter replace,,pipes moving cause old lines to leak...use flash light look under heat shield up at area where rubber hoses conect to metal tubes comming from tank,you may have to loosen bolts that attach to cabin,these harden and split and fuel leaks you need to run car just before check or have running when you check,check for leak along rubber and metal lines all the way to top,,do this after you determine not result of tune up ..when you fill at gas station,check for leakage with large fill hose,, can you smell gas??make sure brakes are not draging,, simple method, just feel all wheels after drive of some distance,,is one wheel much hotter? are all wheels very hot ?compare heat to another car in family have you ajusted E brake recently?? if not related to tune up leak or dragging brakes,if one wheel really hot could also be bad bearing..

[This message has been edited by uhlanstan (edited 09-25-2007).]

those plugs can work fine oir be a real source for problems

I have bosch platinum in my 4.3 V6 89 jimmy got 60,000 miles out of them when they decided to go to spark plug grave yard, 3 went bad at about the same time?? the spark plug spirit wakatanka seem to live in these,, these plugs seem to work better in 3.4 and 4.3 my personal experience with these plugs has been good ..no way would I install in 2.8.. I tried in duke to compare with autolite,new bosch made no improvement over year old autolite,one of few places where you can save money on fiero,,bosch seem to run lean!! ok in gas jimmy not good in fiero,this is based on my limited experience

quote Originally posted by timgray: Lots of posts here about never using Mobil one oil in a flat tappet engine as well. something about the zinc levels are so low the cam will wear out in a hurry if you use synthetic. I do know that synthetics run at a lower oil pressure so your drop is because of switching to a synthetic.

ZDP. Its not really a huge concern, but the cams and lifters will wear faster with low levels of ZDP than with Rotella T. This might mean the difference between 100,000 miles of great cam performance or only 60-70,000. Not a whole lot of difference, you see.

I'm not too sure about the metal-metal contact friction reducing qualities of true synthetics to say that they are worse than Rotella, though.

quote I have bosch platinum in my 4.3 V6 89 jimmy got 60,000 miles out of them when they decided to go to spark plug grave yard, 3 went bad at about the same time?? the spark plug spirit wakatanka seem to live in these,, these plugs seem to work better in 3.4 and 4.3 my personal experience with these plugs has been good ..no way would I install in 2.8.. I tried in duke to compare with autolite,new bosch made no improvement over year old autolite,one of few places where you can save money on fiero,,bosch seem to run lean!! ok in gas jimmy not good in fiero,this is based on my limited experience

Interestingly enough I put a set of platinums on my freshly rebuilt duke and it misfired every now and then under power until I put the old set back on.

[This message has been edited by AP2k (edited 09-25-2007).]

NGK plugs were a Very popular choice a while back

I have run platinum plugs for a while in my 85 2M6, never had a problem till I went to change them after about 50,000 miles, they all broke off where the cermiac met the plug body. They all came out after that, just strange that this happened. While I ran them got 30 mpg on the highway when cruising at 70 and never had any signs of per-ignition or detenation.

RON 768 I bet the plug you removed were white?? they seem to run lean and are britlle to quickly .. this is based on my limited experience,, they will build up a crust of cream looking material if engine is perfect these plugs may give slight increase in mpg but not worth it to try.. they seem to run clean and lean.. cream color instead of light brown.. new post today! gonzo had hose behind heat shield leaking, this is more common on old cars than people know because you can not smell untill leak gets very severe

[This message has been edited by uhlanstan (edited 09-26-2007).]

quote Originally posted by ron768: they all broke off where the cermiac met the plug body.

I have used platinums in all of my V-6 Fieros and never had any issues.....maybe I was lucky, who knows? As far as never using them in the 2.8......never heard that one, but I do remember hearing that the Duke's with DIS didn't run well with them.

A little off topic......I installed a set of NGK iridiums in my Bugeye last year and they worked well until yesterday when the same thing you described happened. It started running rough and when I removed the spark plugs to check them out, one of them broke in half. Crazy.....never had that happen to me. Replaced with "regular" copper plugs......hopefully won't have any issues with them.

I have a set of Bosch Platinium +4 in my 1986 Pontiac Fiero GT, I have the 2.8 liter engine in it and it runs just fine. I also run Quaker State Horsepower synthetic oil, and I have no problems at all. I also have Bosch Platinium +4 in my, daily driver, 1995 GMC Sonoma, with a 2.2 liter in it, it runs great, aside from the truck itself which has no power at all. The truck gets great gas mileage, but I am sacificing lots of power.

I would think that your loss of MPG is a result of something other than your brand of plugs. First hint would be it's now throwing a code 32. I would change the 02 sensor and clean the IAC, check everything and see what ya get.

I got my 87GT/5spd several months ago and it was getting 20-23 mpg. Did a complete tune-up, changed the 02 sensor, cleaned the IAC and now runs great. BTW I get between 38-40 mpg on the highway (very easy cruzinn) and 25 or so in town. It all depends on how you drive.

There have been so many conflicting posts on oil. Let me say that as of Jan 1, 2007 ALL oil that has the API stamp does not have the required amount of ZDP, (additives) for a flat tappet cam, yes even Rotella has been re-formulated to meet EPA guidelines. It is very important to break-in a new cam and lifters with a break-in additive like what Compcams sells. Even after it's broke-in I would still use an additive but it may or may not be required as the new oil does have additives that replaced ZDP. I question though the long term effects, I have too much $$$ in my engines to take a chance.

As for using synthetics in a flat tappet cam engine, absolutely no problem, as long as the engine is broke in before the switch to synthetic and if the engine does not have high mileage.

------------------

2.8 gettin 10mpg, read this1 posted today great info, better than mine especialy about cooling sensor

I think if you were pulling mileage like that from a 2.8 you should switch it all back. 24 in town 32 highway is way good mileage.

I use Bosch Platinum SINGLE tip plugs in everything and have for years. All my cars including the 2 Fieros and 2 Corvettes, my race boat (454 Drag boat), My airplanes, etc. I got an average of 50,000-70,000 miles on a single set in cars I owned long enough. Ive never had a single failure and they never rust in the plug holes. My turboed 3.1 Fiero was on its second set of them at 100,000 when I sold it. The ones in my limos when I owned that business always got at least 75,000 between changes. I put an average of 250K on each of them. My current Corvette with them gets between 25-27 mpg.

[This message has been edited by rogergarrison (edited 09-27-2007).]