Fiero engine problem

[ScotMac]

Sorry, forgot to mention. Yes, the #1 and #3 plugs had a good amount of white on them (tho only on one side of them), which is also why i suspected coolant. But again, i don't think blown head gasket or head bolts, since the compression is perfect on every cylinder.

Oh, and i don't think it is bad enough to show much of difference in coolant level.

Hence my intake manifold gasket thinking. Any other possibilities? Even a slight head gasket problem would show up significantly enough on the compression readings, right?

[schumi]

I would go on Pennock's Fiero forum. They have a ton of experts on that engine on there.

[Team SSR]

Maybe... Cylinder pressures are obviously higher when firing. Did you do a leakdown test with compressed air or a compression test where you spin the engine over with a starter and read the gauge? With a leakdown test you may be able to hear where the air is going and may actually see air bubbles in the cooling system.

[x1/9racer]

Head gasket leakage will not always show a compression problem. These engines back in the day used to frequently break one of the center head bolts, check these bolts for looseness, if they move, most likely they are broken. Also, Snap-On sells a CO2 gas tester for head gasket leakage detection, looks kind of like a turkey baster, a special blue fluid goes in two chambers of the tester, you pull vapor from the coolant filler neck with the engine running, if the fluid turns from blue to yellow, then there is combustion gas in cooling system.

[ScotMac]

I would go on Pennock's Fiero forum. They have a ton of experts on that engine on there.

Yes, Pennock's is the best Fiero forum on the web (though their forum software leaves a bit to be desired). Posted there...i'll see what they say.

Maybe... Cylinder pressures are obviously higher when firing. Did you do a leakdown test with compressed air or a compression test where you spin the engine over with a starter and read the gauge? With a leakdown test you may be able to hear where the air is going and may actually see air bubbles in the cooling system.

Did the latter (spin the engine w/ starter and read the gauge). Haven't done a leakdown test. I agree that the leak down is better at determining head gasket or head issues. But if it is in the intake, the leak down won't show me anything....since the leakdown works by sumitting the cylinder to pressure during the firing phase (TDC). ie, when the valves are closed.

Head gasket leakage will not always show a compression problem. These engines back in the day used to frequently break one of the center head bolts, check these bolts for looseness, if they move, most likely they are broken. Also, Snap-On sells a CO2 gas tester for head gasket leakage detection, looks kind of like a turkey baster, a special blue fluid goes in two chambers of the tester, you pull vapor from the coolant filler neck with the engine running, if the fluid turns from blue to yellow, then there is combustion gas in cooling system.

Again, i agree that those CO2 testers can be useful at determining head gasket and head issues, but again are not as useful for determining an intake leak...since the intake will not be subject to pressure *out*.

[ScotMac]

Also, anyone know what a duke based fiero normally should run for compression, in psi?

[ScotMac]

I just looked at the pressure that a leak down tester works at, from what i can tell, they are used at around 90-150psi. So, to get the same result, all i need to do is do a normal compression check, and leave the pressure in the cylinder, and then listen around the engine to see if the pressure is escaping anywhere. And check for bubbles in the coolant. If it passes that, it should eliminate a *slight* head gasket problem, right?

Edit: Obviously that won't work, since the leak-down is done at TDC, w/ the valves closed, so that it use the air pressure to "press" up against the closed chamber. And also the compression tester has a one-way pressure valve (out only). You guys should have told me before i tried it!!

[88YB1]

Scott, White smoke = coolant, Blue smoke = oil. The water passage in the intake is there to provide quick warm up of the fuel on cold days. From your description the manifold is your most likely cause. A head bolt, head gasket, or cracked head would smoke continuously.

Chuck

[billf]

The other test to do is to cold pressure test the cooling system. If you have leakage at the intake manifold, you should be able to see it. Staining (if you are using antifreeze) should help you locate the leak (external of course). I don't recommend antifreeze, by the way.

Good racing,

Bill