The great misfire question .. help!!

Does this model year 3.1L have injectors? Replacing them on a 98 3.4L cured a single cyl. misfire problem. Might first try some cleaner, such as Chevron techtron. Also does it have the 3 coil setup, firing 2 cyls per coil? Maybe a marginal coil. Spark should be bluish. Are these the original plugs @ 162K miles? Lastly, any signs of the dreaded lower manifold gasket leak which may cause a misfire.

It sure does ... I'd rather not throw injectors at her .. since they are

100.00 a pop, I'll trying some cleaner and see what happens. Blue spark eh .. I'll have to look at that. No, the plugs here replaced 6 months ago, (less than 5k miles). Nope, she doesn't appear to be use any coolant, and like I said, none of the plugs are fowled.

The 3.1 isn't known for injector problems like the 4.3 and the injector designs are quite different. Under what circumstances does the misfire occur and can you tell which cylinder is misfiring?

Oh, the misfire is bad. You can tell at an idle, and feel it under a load. That is where I am hung up, I can't tell which cylinder is having the miss.

With the car off, remove each plug wire from the plug and just place back on the top of the plug without snapping into place. Start the engine and then go around the engine and see which one has no effect when pulled off. Any that have no effect indicate a dead cylinder.

Did you check the coil with an olm meter?

========= Harryface =========

1991 Pontiac Bonneville LE 3800 V6 ( C ), Black/Slate Grey _~_~_~281,040 miles_~_~_

~_~_~_~_U.S.A._~_~_~_~_~_

~~~The Former Fleet ~~~

89 Cavalier Z 24 convertible 78 Holiday 88 coupe 68 LeSabre convertible 73 Impala sedan

I've checked all the coils with an ohm meter. All appear around the same. I don't have a book for the car, so I don't know what exactly is spec. None of the plugs show fouling, but you can smell the gas coming out of the exhaust. I've exchanged all 3 coil packs with a known working unit. No change. This is my wives rig, which is the main rig for hauling the kids around. My Olds, regretfully, has not been maintained, and therefore is not safe for the kids to ride in .. So I am hoping to get this sucker fixed.

When I am testing the Ohm of the plug wires, on the 3 short wires, I get between 6.5 and 5.98 (that is with the meter on 20k, and between 12.0-15.0 on the 3 longer wires. There is one long wire, that if I wiggle the wire in a certain way, the ohm's fluctuate from 19-10 and from 10-19. But, I an not

100% sure it is the wire, and not the connection of the meter to the wire. Man this is frustrating.

Is this a question of semantics?

The Multec injectors used in the 3.1 are -very- prone to failure.

Yep, new injectors are expensive so I bought a set of reconditioned for about $150 exchange from

. From other newsgroups, this outfit seemed reputable. Got about 10K miles so far. I had gone the same route as you, checking plugs, wires, swapping coil packs around, even checked fuel pressure (which you might do if original fuel pump) and decided the next shot was the injectors.

FWIT- I had a 94 3.1 breaking up after 3k rpm's. Took it to the shade tree machanic. He changed all the coil packs with no change. I had replaced spark plugs previously and the wires all check out good. Even did an electrical load test while diving.

Luckly I was venting antifreeze on the upper left of the engine and water spray into the spark plug area and a sharp blue spark knocked me back on my heels. Did it again with the same results.

Checked the boot of the spark plug wire and it was fine. Removed the plug and inspected it closely. A cracked porceline! A fine hair crack up the side of the porceline. Changed the plug and all was well.

Hope this helps.

Thanks! I've changed out all the plugs, and the wires, and looked for arcs coming from the plugs..

In 3.5 years at an Olds dealer from 1999-2003, I never replaced a single

3.1 injector.

replaced four injectors in 3 engines in less than 2 years now.

tomato tomoto

also check resistance of coils. are you sure it is a misfire. my wife thought it was a misfire and turned out to be a bad vacuum hose. test injectors for 12 ohms resistance across the terminals. if this started not to long after the tune up it may have a cracked plug. pull them out and make sure the ceramic doesnt move and look for carbon on the ceramic.

Eight years in a Chevy dealership, I replaced hundreds. Went to Ford dealership, replaced many more on GM vehicles. Switched to the Chrysler Plymouth dealership next door to the Ford dealership, replaced even more Multecs. Hired on at natural gas utility, fleet mechanic, replaced yet more Multecs. Quit gas company to work for Snap-On as technical equipment specialist, found even more faulty Multecs during equipment demos. Promoted to regional training manager after Snap-On acquired Sun Electric, faulty Multecs still out there. Changed jobs to become head IM-240 referee for the state of Wisconsin, you guessed it, more faulty Multecs diagnosed. Currently own repair shop (last 7 years), still making customers happy and engines run right replacing faulty Multec injectors.

Sorry HT, your 3.5 years don't really stack up against my last 20.

I had the same problem on my 97 Grand Am with a 3100 engine. It turned out to be a bad fuel injector.

Bit your tongue .. Bit your tongue ..