I gott'a 90 Firebird v6 MPI and the problem i am having is that it idles fine but when i put a load on it, or try to go up a hill the engine bogs down and either feels like its gonna stall or backfires out of the exhaust. I have changed the following...


Cap/Rotor/Plugs/Wires/O2 Sensor & I have done a fuel pressue test which seem to be fine, some have suggested a plugged cat. what does anyone else think?

 

It could be an exhaust restriction, although I'd look for either a vaccum leak or your timing if off. Check your timing first, and if that's o.k., then check all your vacuum hoses, especially the ones at the back of the plenum. If those are all fine, take it to an exhaust shop, they can do a test for an exhaust restriction.

 

Sounds like timing to me.

 

I was also thinking a clogged cat; how does it drive on a flat road if you floor it? Does it seem like you're not flooring it? I drove an '83 camaro with a clogged cat; it was strange.. I floored the gas and nothing changed; the car just chugged along like my foot was off the gas. But the backfiring sounds like timing, or low fuel pressure- did you do the test with a gauge?

 

i used a pressure guage and according to the numbers with just the key on and with it idling the pressure is within satisfactory ranges, to answer tomp's question on flat ground when i floor it it doesnt have the power it used to have all the time or it will take off fine then bog down. im leaning more to the cat myself but will take as many suggestions i can get.

 

Use the shack test on the cat as a quick check and take a look at it after you have been driving a while and look to see if it is glowing orange or red or is super hot.


I agree with Camar_Hunter_c, sounds like timing problem, real easy to check.

 

With a clogged cat the engine WILL eventually stall, not just lose power. Go drive for a while, if the cat is glowing red after 2-3 miles, then its clogged, if not you have other probs.

 

could also be injectors how many miles you got on it? i think it needs fuel injector cleaning not just the bottle in the gas either i mean teh potent stuff thats ran directly into the fuel rail pepboys does it 69.99 it might also be the cat though have someone rev it while you hold your hand over the exhaust if it hesitates you need a cat if it trys to pull your hand in you have internal problems with the engine :-(

 

michael be careful with that potent stuff, GM warns you right in their factory manuals that that stuff can eat at the o-rings causeing more harm then good. Injector cleaners are a lot of BS, the way GM tests injectors is to hook up a pressure gauge to the line and use their tool to activate each injector one at a time and watch the pressure drop. This will tell you which injecotor is good and which is weak and which is pissing to much. Injectors don't get dirty LOL, thats what a fuel filter is for and gasline has cleaners alreay in it to stop any type of guming up. So don't waste your money on cleaners. Just get the GM tools and follow the GM test in the factory manual.

 

Michael, you could send them out to Rich J at http://www.cruzinperformance.com for a disassembly & cleaning for less than the Pep Boys price! Ryan, if you want that injector tool, http://www.sunpro.com sells it through their "garage sale" link! The injectors can get dirty, depends on how clean the gas is, and how long the car sits for. When RichJ cleaned my spare set of injectors, the car felt stronger with them in, as opposed to my original 180,000 mile set.

 

I didn't read everything but...

I noticed a big difference in idle when I had to change my cat! Much smoother. So a restriction could be your problem...

Also check your timing. It should hold a STEADY ten degrees or so. A lot of us use around 12 degrees or so for better idle... How many miles are on the car? A worn timing chain (thats usually takes about 80k to do) can cuase an erratic idle. Replace that timing chain with a Coyles Double Roller Chain Set from www.SummitRacing.com for like 90 bucks or so...

Hows your Vacuum? THat cuases TONS of problems. Learned that the hard way. If you don't have a guage, do a poormans check, by pulling a hose by the Purge Canister (Black cylinder opposite the battery side). Make sure you hear a hiss. No hss means you don't have any pressure. I recomend buying a guage(like $20 or so) and makeing sure that you have 16 t0 20 psi...

 

Go look at your coil in the dark and see if it glows, you probley need a new one.

 

the car has about 140K miles on it, im thinking of just taking it in cause i dont get enough free time from work to mess with it, on my days off i usually like to just lay around cause im so wiped. but when i get a chance i try some of everyones suggestions, i just hate to pay a butt load for it, just had to pay 1,500 for a transaxle in my current daily driver.