Thread: 2004 grandprix wont go over 70 mph

CEL flashing = multiple random misfires. Torque converter will not cause that.

Clogged cat or really bad ignition parts. Pulgs wires ect. Bad cat would be best best guess tho.

if the tune up involved just plugs, then you need wiresm even cheap wires that are bent too tight seem to fail fairly quickly after install

if its the cat the engine wont rev to high rpm's even in 1st/2nd gear.

what yer describing is a high load misfire.... use a handheld spray bottle at night and soak down the ign cables/coils with soapy water and look for a lightning storm.

chances are if its been doing it for a while you wont need to load it up to get it to mis

Do not replace the cat, you are wasting money.

Like 2 others have said, flashing check engine light is a misfire. You need to fix that first.

And if it is the cat and you take it for a spirited drive and you look under the car that sum ***** should be glowing hot

drive it at night, then pull over to see if the cat is glowing red.

when cold you can also bang on the cat and listen for busted material inside.

Clogged cat will cause misfires. Best cat test is back pressure measurement at upstream o2 sensor bung. Other indications are quiet weak flow from tailpipe, exhaust fumes blowing out of manifold seals in engine bay, weak acceleration in lower gears especially on upgrades, engine temp rise after laboring up a long upgrade. Mine did not glow red hot as others described.

If you have new plugs, but not new wires, change the wires, eliminate that variable from the equation before the expense of the cat decision has to be made. In my experiences with bad wires, you will for sure have problems with high speed misfires, and also under high load when accelerating at lower speeds, you will feel those and may not actually see OBD II misfire codes thrown. It may idle relatively smoothly, and even when revving in neutral, but go rough as soon as there is load put on the engine.

When you did your tune up, did you make the common mistake of putting the dielectric grease on the tips of the plugs and onto the contact surfaces of the connector inside the wire boots? The stuff is an insulator, the last thing you want on an electrical connection. Its just supposed to be lightly swiped on the rubber inner diameter of the boots with a Q tip to seal out moisture.

Originally Posted by Fivefingerdeathpunch

Do not replace the cat, you are wasting money.

Like 2 others have said, flashing check engine light is a misfire. You need to fix that first.

Bad cat can most definitely cause misfires. Back when I was around 14 or 15 and was first allowed to drive my moms grand prix I actually drove nice and never noticed the failing cat untill I got a flashing CEL for random missfire, Then I finished melting down the cat by driving 15 miles home anyways with raw fuel going into the dieing cat. Mom was pissed. Car limped to the shop at 15mph. Now that I bought the car from her the cat disappeared. Cant say I miss it at all. E85 smells awesome.

I do agree that they should eliminate the chance that its ignition related first though.

I love smelling like a distillery....

Originally Posted by Turbocharged400sbc

I love smelling like a distillery....

Sir, have you been drinking? No but my car has!