1985 Pontiac Fiero SE

Tiny
MX~MASTER
  • MEMBER
  • 1985 PONTIAC FIERO
My car will only fire in 3 cylinders and will only start by priming it. And when it is running and I floor the gas it doesn't go above 1000 rpm. I am thinking it something might be wrong with the intake valves.
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Monday, July 24th, 2006 AT 4:04 PM

25 Replies

Tiny
MIKEYBDMAN
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Have you checked to see if you are getting good fuel pressure?
Do a compression check on all of your cylinders to eliminate intake vavles.
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Monday, July 24th, 2006 AT 5:11 PM
Tiny
MX~MASTER
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I just replaced the intake manifold off another feiro I had and it didn't do much. How would I check the compressison
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Monday, July 24th, 2006 AT 9:35 PM
Tiny
MIKEYBDMAN
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You will need to either buy or borrow a compression gauge. Remove all of your sprak plugs, and you will need to disable the ignition circuit. Screw the compression gauge and hose into the spark plug hole of the first cylinder. Have someone turn the engine over about 3 revolutions and you will see the pressure build and stabalize. I would think you should get atleast 120 psi or more on each cylinder. But most likely if you have one bad cylinder, it will be alot lower than the others.
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Tuesday, July 25th, 2006 AT 3:02 PM
Tiny
MX~MASTER
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You will need to either buy or borrow a compression gauge. Remove all of your sprak plugs, and you will need to disable the ignition circuit. Screw the compression gauge and hose into the spark plug hole of the first cylinder. Have someone turn the engine over about 3 revolutions and you will see the pressure build and stabalize. I would think you should get atleast 120 psi or more on each cylinder. But most likely if you have one bad cylinder, it will be alot lower than the others.[/Quote:9d11bd49fc]

I checked my compression but it still is good enough that it should all be firing?
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Wednesday, July 26th, 2006 AT 1:02 AM
Tiny
MIKEYBDMAN
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Have you checked to see if that spark plug is firing? You need to check for aprk at that plug. Look for a bad apark plug wire, or bad spark plug. Could be not getting enuff fuel pressure to run smooth also. I would check your plaugs and your fuel pressure. If you are getting good fuel, good spark, then that leaves timing.
In re-reading your original post, you fuel pump may not be pumping properly. I would check fuel pressure next. This is how the manual describes a fuel pressure check.

FUEL SYSTEM PRESSURE RELEASE

4 & 8 Cylinder Engines

With engine Off, remove fuel pump fuse from fuse block.
Start engine and allow to run until fuel supply is exhausted.
Crank engine an additional 3 seconds to ensure fuel supply is exhausted.
Install fuel pump fuse.
On 4-112 and 4-121 overhead valve engines, install fuel pressure gauge between throttle body side of fuel filter at the rear of the car. On 4-151 engines, install fuel pressure gauge between TBI unit and steel fuel line. On V8 engines, install fuel gauge between front and rear TBI units steel fuel line.
Start engine and observe fuel pressure. It should be 9 to 13 psi.
Relieve fuel system pressure. Refer to steps 1 through 3 above.
Remove fuel pressure gauge and reinstall fuel lines.
Start engine and check for fuel leaks.
FUEL SYSTEM PRESSURE TESTING

Before servicing fuel system components, fuel system pressure must be released. To relieve pressure, proceed as follows:

Remove fuel pump fuse from fuse block.
Run engine until fuel remaining in lines is consumed. When engine shuts down, engage starter for approximately three seconds to relieve any remaining pressure.
With ignition off, replace fuel pump fuse.
Remove air cleaner and plug THERMAC vacuum port on throttle body unit.
Remove fuel line between TBI unit and fuel filter or between front and rear TBI units on Crossfire'' injection systems. Use a suitable back-up wrench to hold flare nut on throttle body when removing line.
Install fuel pressure gauge J-29658 or equivalent, between throttle body and filter or, on Crossfire'' systems, between front and rear TBI units.
Check pressure reading with engine running. If fuel pressure is not between 9 and 13 psi, refer to Fuel System Diagnosis.''
De-pressurize fuel system, remove pressure gauge and reinstall fuel line.
Start engine and check for fuel leaks.
Remove plug from THERMAC vacuum port and install air cleaner.
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Friday, July 28th, 2006 AT 2:39 PM
Tiny
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I tested the compression and its good enough still that they should all be firing and there is spark. I changed the fuel injectores and it seemed to get worse now its only firing in one cylinder and backfires
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Saturday, July 29th, 2006 AT 3:40 PM
Tiny
MIKEYBDMAN
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I would check the fuel pressure. I posted instructions on how in an earlier post.
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Saturday, July 29th, 2006 AT 4:03 PM
Tiny
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I checked the fuel line pressure and its alright could it be the timing or the computer?
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Monday, September 4th, 2006 AT 4:14 PM
Tiny
MX~MASTER
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Anyone with any other ideas?
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Wednesday, September 20th, 2006 AT 9:46 PM
Tiny
MX~MASTER
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I got the problem fixed it was the book the firing order they have wrong in the book so we changed the spark plug wiring different but its still not firing in one cylinder do u think it could be a dead injector?
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Wednesday, April 4th, 2007 AT 11:17 PM
Tiny
MCFERRANCE
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Have you thoroughly checked the ignition system?

Is this a 4 cylinder?

I believe that this has a distributor cap. Do you have spark at each cylinder? Have you replaced the cap and rotor? Have you checked and/or changed the plug wires and plugs?
Another thing to do is to unplug the wire connection at the distributor and check and clean them, and also spread the male terminals to get better contact. I had a problem with this connection that was corrected by doing this.

You may need to check the ignition timing also.

If this is a 4 cylinder it has a TBI and 1 injector, correct?

If this is a 4 cylinder, it is unlikely that the camshaft and crankshaft jumped time and would still run. If it is a 6 cylinder it could jump time and still run, although not very well.
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Friday, April 6th, 2007 AT 2:49 PM
Tiny
MX~MASTER
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Yeah it is a v6 and it is running just not on all cylinders, and we got the plugs down to one injector so if we change the 6th injector it should be good
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Friday, April 6th, 2007 AT 3:24 PM
Tiny
MCFERRANCE
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Isn't this a 2.8L with a TBI and 2 injectors? Does this have a distributor?

The more specifics we have about the engine size, ignition, injectors and such, the easier it will be to help you.
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Friday, April 6th, 2007 AT 4:39 PM
Tiny
MX~MASTER
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Yes its a 2.8L and it has a distrubtor and 6 injectors
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Friday, April 6th, 2007 AT 8:32 PM
Tiny
MCFERRANCE
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Let us know if the injector takes care of it.
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Saturday, April 7th, 2007 AT 6:45 AM
Tiny
MX~MASTER
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Its still not running on one cylinder
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Thursday, April 12th, 2007 AT 10:32 PM
Tiny
MCFERRANCE
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Are you sure that you have good spark at each cylinder.

If you are sure that it is the injector, the next thing to check would be the wiring to that injector and then next would be the computer.

There are "noid lights" available to insert between the injector and the wiring plug to see if it is getting its electrical impulse from the computer. This should be available for your application. They should be available through a parts store or tool dealers such as Snap-on, Matco, or Mac.
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Friday, April 13th, 2007 AT 9:47 AM
Tiny
MX~MASTER
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I have gotten it to run in all 6 cylinders now, but my idle is way to high and my engine is overheating. I tried pluging an open vacume hose and it idled it down to where it should be, but when I attatched the vacume line to the intake manifold where it should be it, the idle went way back up like before, I am clueless on what I should do?
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Tuesday, October 23rd, 2007 AT 11:38 PM
Tiny
MCFERRANCE
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What does this vacuum line go to?

It sounds like the vacuum line is leaking from a tear, crack, or hole in it; that it isn't hooked up to what it controls, or the part that it controls is faulty and leaking.

One other thing would be to check if the vacuum lines are ALL hooked up correctly. Especially check the parts that have 2 vacuum lines on them to make sure they aren't hooked up backwards. Some applications have check valves in line. If these are backwards, it would cause a vacuum leak such as you describe.
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Wednesday, October 24th, 2007 AT 9:50 AM
Tiny
MX~MASTER
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The hose goes from the underneath carburator to the intake manifold, its a pretty big line, and to me it seems like its the only place to go because of a metal hose which doesn't allow bending to anywhere else the peice fits there, and I cant find any other lines for those two to go other than that. And when the one hose coming from the bottom of the carburator is not pluged the check engine light is on.
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Friday, October 26th, 2007 AT 11:24 AM

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