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Making sense of sensors by Rich Truett
Started on: 03-16-2015 07:13 PM
Replies: 8 (206 views)
Last post by: 2.5 on 03-19-2015 04:05 PM
Rich Truett
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Report this Post03-16-2015 07:13 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
So...I recently bought a 1988 Formula from the second owner, a retired GM engineer. Total mileage: 55,000.
The car appears to never had a tuneup. I replaced original spark plugs, cap, rotor, wires, etc.
None of the maintenance cured a nagging problem: When cold, the engine runs very, very rich and will not rev past 3,000 or so RPM.
The codes thrown were 34 and 42.
I replaced the 02 sensor, the coolant temperature sensor, the MAP sensor. I found and fixed three vacuum leaks, including the EGR tube, which was cracked. I cleaned the upper intake while it was off and the throttle body as well.
The previous owner did recently replace the Ignition Control Module (ICM).
Finally yesterday, on a whim, I replaced the ICM and lo behold the car runs perfectly now. steady idle at 900 rpm, starts nicely when cold.

A few remaining small items to fix, including the dreaded trunk-side exhaust manifold.

Some questions:

There is a tube that appears to just stick in the bottom part of the throttle body. I can see that producing a small vacuum leak. Is there supposed to be any kind of sealer/o-ring around this tube? On my car it just fits inside.

What is the best way to remove that trunk side exhaust manifold. You can't see most of the manifold bolt from either the top or the bottom of the car.

BTW: This is my first Fiero since the early '90s. Neat car.
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Gall757
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Report this Post03-16-2015 08:17 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
Welcome to the Forum!

I thought the dreaded one was the one under the window....Do you have a crack in the rear manifold?

[This message has been edited by Gall757 (edited 03-16-2015).]

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Rich Truett
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Report this Post03-16-2015 08:30 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
Oops. You are right. It is the exhaust manifold under the window.

I think it is cracked. I have the ticking sound. I took it the car to Midas Saturday. They put it on a lift and started it and then got under it with a stethoscope. They traced the noise to the back part of the manifold right at the head. That would be the section of the exhaust manifold closest to the rear of the engine, (driver's side). My car had the recall and has the heat shield on the exhaust, further complicating things.

They also discovered the catalytic converter's innards have broken loose. So that will have to be replaced.
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Gall757
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Report this Post03-16-2015 09:02 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
I don't think you will ever remove that manifold from the top. It may be just a bad gasket and not a crack....but it still has to come off the head, which is always an adventure. If your car has been well protected over all these years, the bolts may be OK.
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Rich Truett
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Report this Post03-16-2015 09:09 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
You might know my car, Gall.
It has Michigan Fiero club stickers all over it.
It was owned by the former president of the club's wife, I am told by Floyd, the previous owner.

I have really enjoyed getting her running well.
Brakes are up next and then I am thinking of doing poly bushes.
But this exhaust manifold leak is troubling.
I am thinking maybe I will just pull the head off and handle it that way.
Can anyone recommend a good Fiero mechanic in the Detroit/Southeast Michigan area?

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fierogt28
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Report this Post03-16-2015 10:26 PM Click Here to See the Profile for fierogt28Click Here to Email fierogt28Send a Private Message to fierogt28Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rich Truett:

So...I recently bought a 1988 Formula from the second owner, a retired GM engineer. Total mileage: 55,000.
The car appears to never had a tuneup. I replaced original spark plugs, cap, rotor, wires, etc.
None of the maintenance cured a nagging problem: When cold, the engine runs very, very rich and will not rev past 3,000 or so RPM.
The codes thrown were 34 and 42.
I replaced the 02 sensor, the coolant temperature sensor, the MAP sensor. I found and fixed three vacuum leaks, including the EGR tube, which was cracked. I cleaned the upper intake while it was off and the throttle body as well.
The previous owner did recently replace the Ignition Control Module (ICM).
Finally yesterday, on a whim, I replaced the ICM and lo behold the car runs perfectly now. steady idle at 900 rpm, starts nicely when cold.

A few remaining small items to fix, including the dreaded trunk-side exhaust manifold.

Some questions:

There is a tube that appears to just stick in the bottom part of the throttle body. I can see that producing a small vacuum leak. Is there supposed to be any kind of sealer/o-ring around this tube? On my car it just fits inside.

What is the best way to remove that trunk side exhaust manifold. You can't see most of the manifold bolt from either the top or the bottom of the car.

BTW: This is my first Fiero since the early '90s. Neat car.


Hi Rich, welcome to the forum.

About the throttle body...it has an o ring seated outside the metal tube to seal with-in the throttle body. The bottom of the tube goes into the lower
plenum. I suspect this is what your asking about. Like you mentioned you took the TB off for cleaning. That would of been the best time to
see the o ring seal inside. The o ring is seated in a groove in the throttle body. This...you need to have.

I hope you replaced the ICM with a new AC Delco unit. The aftermarket ICMs have a tendency to have a short life. Make sure to add some heat-sink
grease underneath the ICM and the 2 screws are very clean, or install new GM ones at 10$ / pr. I'm saying this to benefit you to have a trouble free ignition
system for years to come.

One pointer about the cracked manifold. Most folks don't know this, but don't open the deck-lid when its raining and the engine running. Try to avoid that.
The reason is the water from above falls on to the hot manifold and that gives a temperature shock to the steel and the manifold will crack over time.

Have fun with the car, and you did a good choice getting an 88.

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

fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

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Spoon
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Report this Post03-17-2015 09:39 PM Click Here to See the Profile for SpoonSend a Private Message to SpoonEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you plan to tackle this manifold job yourself it would be wise to have a second person involved. Their job would be to pray for you, on both knees if necessary. I speak from experience, this will be your most miserable encounter you will ever have with a vehicle.

Don't get me started...........

Spoon

------------------
"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

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Rich Truett
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Report this Post03-18-2015 08:42 PM Click Here to See the Profile for Rich TruettClick Here to Email Rich TruettSend a Private Message to Rich TruettEdit/Delete MessageReply w/QuoteDirect Link to This Post
I am not sure yet if I love the car enough to do the window-side exhaust manifold fix.
It looks like a real bear of a job.
But I wonder...

Would it be easier to pull the cylinder off and take care of it that way? At least you do 98 percent of the work from up top.

However, things are tolerable now. My car had an aftermarket Dana cruise cruise system installed somewhere in its past life. I say had. It didn't work and now the trash can has cruise control. Anyway, the wiring was routed through the console and into the engine bay by unplugging a very large square grey plastic wiring harness grommet type fixture that plugs into the engine bay firewall. Once I removed the cruise control wire harness and reinstalled that plug, it cancelled out 80 percent of the engine noise oozing into to the interior.

My plan is to reduce back pressure by bypassing the catalytic converter with a test pipe. The cat con is broke anyway. reducing the backpressure by removing the converter could quiet the exhaust leak a bit. At least I hope.

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2.5
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Report this Post03-19-2015 04:05 PM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
Welcome to the forum
Whatever you decide with removing the exh manifold, I'd start hosing those manifold bolts with PB blaster penetrating lubricant, and stop driving it, (because PB is flammable).
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