i have a leaky front side exhaust manifold, and am getting REALLY bad mileage.. haven't had a chance to fix it, but was wondering, i am getting 100-150/tank ever since i started driving the car again, and the manifold was not loose when i used to drive it (haven't driven regularly in more than 6 mos. - was parked after i bougt my maxima) the way i think is, maybe air is getting into the exhaust stream and tripping out the 02 sensor? any input? i would think that air couldnt get into the pipes, due to positive pressure, but perhaps after the exhaust pulse has gone by theres a bit of a vacuum? the engine has less than 20k on it, 190 thermostat, runs great, except for smelly exhaust, and no codes being thrown

yea... i also have a craked manifold. but my 86' GT has 120k on it so i didnt think it was a problem that i only get 130miles a tank. but if the manifold can get me more miles, i'll get that fixed. let us know? anyone?

same for me. before i started hearing the leak i was getting about 150mls from full down to 1/4 tank. it's down to about 120-130 now. have to say i think a tune up is needed also.

Yep, exhaust leak ahead of the oxy sensor will def cause a rich mixture and poor gas mileage....had it happen on a 88 of mine. You may need to replace the sensor too after you fix the leak if it doesn't get better. Good luck!

Phil

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GTDude
OVER 25 years GM experience

A crack in the exhaust up stream from the O2 sensor will definatly screw up performance and mileage.

Any crack, depending on where is is, can cause major damage as well. Under the right conditions even cause a fire.

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11-Sept-01, The day the world as we knew it ended.

well my 85 GT 2.8 V6 has a 4sp manual gearbox.
The engine is in A1 condition and i only get 130 to a tank max. !!!

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Regards,

Paul Taylor, England.
85 GT, 2.8 V6.

looking at the registration dates of most of the people in this message, do i qualify as an old school member? theogre rules, i remember him... so many people now!

Hey Paul

I have the same car and get 27 mpg on the highway...I would bet if you pulled your O2 sensor it will be as black as night....for an easy test you can unplug the O2 and see if your mileage improves....

Rick

Yep,FIRE is a coming!!! Screw the rest...THAT my friend WILL indeed cause you more pain than loosing a few miles per gallon.
Then again maybe you like fire.....

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Damn woudnt you know it, the 85 V6 i just bought has the same problem. Does GM make this part still? I am afraid to touch it cause i dont want to break off the bolts tryin to remove it lol, I havent looked up there yet, but can i get the mig welder into there and shut the crack without pulling it off the car? Anyone doen this?

And yes i know how to weld on a car without frying things.

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'85 SE v6 auto (daily driver)

'88 Red SE (4.9 PFI, 4T60E 4speed O/D trans, Custom cradle) Engine installed! Fastback conversion begins.....the fun just keeps multiplying!

If the fix is a NEW pair of manifolds, I happen to have a new GM-DELCO pair. I am now working on my V8 Fiero so the V6 stuff ain't doing me anymore good. I have several O2 sensors if needed also ($13 ea.).
The manifolds I will sell for $230 which includes shipping in the US.

i got my car from a pawn shop so i didn't talk to the owner, but there was a reciept for manifold repair in the glove box so i know he had it done at some time. it looks like maybe just before he pawned it. and it's a common problem here.

are there any cast manifolds that could be used as a replacement? these things don't look like they're anything special, tuned or anything. could i use some off a 2.8 blazer, 3.4 engine or something? i'd be happy to trade a few horses for something that dosen't have to constantly be repaired. the constant cracking seems to messing up the performance anyway.

Scavenging is the effect that will pull fresh air through the crack, into the exhaust and over the oxygen sensor, producing a lean reading at the sensor,and poor gas mileage. Turbos are brutal on the stock manifolds in addition to the heat produced by stock settings. For those of you who have the equipment and the skills here is what I did: I took a pair of late model front wheel drive cast iron manifolds (two left sides)elongated the bolt holes vertically to fit the cast iron heads, used long bolts with tubular sleeves to secure them to the cylinder head, and for the right side, cut the manifold in two places and welded it back together on the cylinder head making it a right handed manifold, there is somewhat of an offset to the rejoined pieces but, the ports and tube section are much larger than the O.E. equipment. It takes a lot to make them glow which means more durability and hopefully no more trouble with cracks and leaks. I'll need to get my camera back from a loanee if you want pictures.

Yeppers, poor O2 will give bad gas mileage, cracked exhaust manifold will ruin head, warp valves, create lots of heat. (sounds bad too)

Ed

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http://hometown.aol.com/idomy0wnracing

that's what i was thinking. that the 3.4 ones might flow a little better anyway. i don't know if i can pull that kind of work off though. i'd like to see the pics please when/if you get the chance or time.

quote Originally posted by Paul Taylor: well my 85 GT 2.8 V6 has a 4sp manual gearbox. The engine is in A1 condition and i only get 130 to a tank max. !!!

Do you run out every gear??? Sheesh...I have an 85GT 2.8L 4 speed and I get about 200 miles out of a tank...and I've got an exhaust leak...hmmm...I should get that fixed...

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Nick
AIM: Naskie182010 www.naskie18.com

Someone said that the front (looking at engine from trunk) manifold can be removed with the engine in the car...? I too have a leak and would like to get it fixed before it gets too cold!

Fieroman

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~ Shane
AIM: fieroman500

Love it, admire it....tear it apart!

The exhaust manifolds I modified are front wheel drive manifolds that exit in the same location as the O.E. manifolds. The camaro/firebird manifolds are not practical because of the exhaust exit outlets. In order to remove the front manifold you must loosen the a/c compressor and remove the three bolts that mount the bracket to the head so that you can push the assembly forward to get to the lower flange bolt. If you really want to make it easy, disconnect the dog bone, support the car just ahead of the front cradle bolts, remove the rear cradle bolts and let the cradle swing down a few inches, be careful not to break any wires or grounds. It will be about to days before I can post pictures of what I have done.

It's certainly possible to remove the front manifold whilst the engine is in the car. I would heartily recommend, if you don't have one, you beg, buy or borrow a 3/8" "butterfly" impact wrench and impact sockets (and a spare socket, too...).

With my '88, I had to let the thing whack away for over a minute on a couple of studs, but out they came eventually. Hold on tight and let the air do the work. The constant vibration weakens even rusted bolts.

Eventually.

got the damn thing fixed - came up with a few new modifications that i highly recommend - heres some ideas for y'all -

the problems was not a cracked manifold, or a loose bolt - it was caused by the damn heatshield that gets sandwitched between the manifold and the gasket - it cracked, and allowed the exhaust to leak - i remember on 2 other fieros that the heatshield caused problems with blowing the gaskets out and such, so i decided (with some help from my dad) to cut the heat shield in half along the exhaust ports, and put those on top, outside the manifold, between the washer for the manifold bolt, and the exhaust flange. we took the manifold, rtv'ed the top 3 pieces (tiny!) to the back of the flange to hold them in place, and put the manifold where it needs to be, then put on the other (lower) half, and put the bolts in. so far, no more ticking noise, car runs smooth, but still smells rich... 02 sensor is not hard to swap out, just a pain..

on my test drive, though, the car died 2x- turns out to be an unrelated problem, with the charging system. the alternator and battery are both about 2 years old, but only 10-15k miles... anyways, another day, another problem.. i will post pics when i get a chance )if anyone is interested in seeing what i mean? i also left the ac compressor off the car, until i am sure its not going to start leaking again... can an autoparts store check to see if i have a bad battery, or can they only check alternators?

So what's your mileage after the fix?