The car is a 91 firebird 305 and is my daily driver. Performance is not a huge deal with this car since I just use it to get around, but the misfire problem bothers me because I plan to sell it soon and I know nobody will buy it for a whole lot this way.

The car accelerates fine up until 3500 rpms or so and then it just feels like it hit a brick wall. The rpms more or less stick or climb maybe a few rpms a second but there is absolutely NO power. The tach goes up decently fast until 3500, then it just stays there. Once I let off the gas the car will shift and all is well again. Initially I thought a fuel problem ... clogged filter, bad pump? Filter looks to be relatively new, pump I'm not sure about. The car is a tbi setup car, so any obvious things I could check for? Maybe a bad injector? Oh, it has an intake manifold gasket leak in the back, but I don't think that would cause this bad of a miss, seems more of a fuel delivery problem.

 

Check the fuel pressure. Low pressure would point to a shotsky pump or regulator.

 

yea that was my original thought, I was leaning towards the fuel pump to begin with. I'm assuming the line just needs to be seperated and a guage installed with a T fitting? Tbi cars don't have the luxury of a schraeder valve?

 

can't help you there. TBI didn't last long in my car. Just follow the lines up, if there's a valve......you'll find it

 

None of the ones I've seen. Be sure to use a backup wrench because that throttle body can very well crack if you don't.

 

Yeah you'll need to run a schrader valve in-line with your fuel line, before it goes to the TB's...make sure you dont get a return line....

I dunno if you have a Harbor Freight there, but I have a gauge set from Matco and I went to Harbor Freight and bought the fuel pressure set for like $10 and not only got a gauge but primarily got all the hoses/fittings to plumb a schrader valve into systems not designed for one.

 

Thanks guys I'll try and pick on up in the next few days. There's a harbor frieght within 20 miles or so.

I finally got the brakes done today ( wheel locks and no key ) and I put it on the lift and noticed that it has an intake manifold gasket leak that is sorta bad. ( lots of oil on the back of the engine / trans ) When I started the car it would also kind of whistle from the engine bay ( almost like it's supercharged ) and if I gave it a slight rev the noise came away. I'm assuming this is air being sucked in through the torn intake manifold gasket. I'm also assuming this could cause a high rpm miss as well since it woulid be running lean in those cylinders with the leak. Any input?

 

I took the car out today and got on it in 3rd gear. In 3rd gear the misfire happened at only 3300 rpm. I'm assuming I'm running out of fuel for sure. Also if I start the car with a warm engine sometimes it dies out unless I quick rev it. Sounds like maybe the pump is giving out, but then again wouldn't it die out on a cold start too?

 

I had this problem and found it was a faulty ignition module (?)(Under the Dist. Cap). It was not making connection properly - I figured for the price I would change it out anyway.

 

Warm start issues, unless theyre no-starts, tend to be associated with faulty fuel injectors....they leak down and get into the manifold and when you crank it the motor goes real rich for a second and wants to shut down, the rev clears it. Revving a LEAN motor due to low fuel pressure, should actually cause it to shut down cause youre just further leaning it. The drop in manifold vacuum upon rev will up the fuel pressure, but if the system isnt right and cant respond fast enough, it should die or want to cut out as it falls off of the rev.

If the injector isnt spraying properly or too much it could also cause your misfire. TBI motors only have two, mounted in the throat....could always ship em out to an injector shop to have em checked/rebuilt if youre unsure, but of course you'd be down a car for a little while, not sure if you wanna do that.

 

Well if I meassure the resistances and they are both good that would mean the injectors are good right? There is a good chance an injector is leaky because on start to the car does smell like fuel and even sometimes after shutdown. This would show on a resistance test right?

 

I still haven't gotten around to doing this, however if resistances are out of spec then they are obviously leaking or not opening at all right? If resistances check out I can have someone turn the key to the on position and look and see if any of them squirt fuel? Both should remain dry until the engine cranks correct?