when i raump on it and shift through the gears my car seems to feel like it is not getting enough fuel when it hits about 4K in 2nd gear....its a stock CCq-jet and i JUST replaced the choke pull-off selenoid cuz the old one was bad.....any suggestions?

it ONLY does it in 2nd gear under WOT too...i dont get it...it surges really bad until u let off and shift......

 

Sounds like fuel delivery.

Fuel pump, fuel filter, crusties in the tank, etc. etc.

 

Heat Soak in the fuel lines. Guaranteed.

 

what is heat soak?

and how would i get rid of it?

 

The fuel lines get so hot that the fuel boils / vaporizes when it get to the carb bowl. Heat soak is otherwise known as vapor lock. Carbed thirdgens fuel line routing is so tight to the engine it is almost unavoidable. In factory form GM fought this problem. I ran my fuel lines up the drivers side with an electric pump. This helped alot. Most importantly if you have the really small heat shields on your fuel tank then buy the sheilds from a 91-92 Z28. These sheilds will completely cover the tank area and keep muffler heat from cooking the fuel.

 

I had the SAME EXACT symptoms as you a little over a year ago. I even noticed I was worse after idling for extended periods of time in hot weather (NEVER happened in the winter) After installing a gauge I watched my FP drop to under 1 psi during when the problem occured.

I fixed my FP problem with a good pump setup, removed the stock inlet filter and installed an inline filter, and fabbed up some heat shielding around the line in the engine bay. Problem solved.

CamaroMike - GM fixed the problem with an auxiliary electric pusher pump in the tank. All 87 models got the pump. GM issued a TSB to install this pump if the owner complains of vapor lock, so some 82-86 cars have it.

 

The last time I experienced the same type problem. I was at the track and I was manually shifting it, when in 3rd gears at about 4k rpms my engine was starving for fuel. It turned out the fuel pump push rod was not reaching the mech pump anymore it was bent *(stuck) . The fuel pump was not good either. I switched to an electric fuel pump due to not being able to remove the rod and the problem went away.

 

Marc,

Don't forget the little fan that blows on the carb, the redesigned jets, and the different needle and seat that GM also sold to help reduce the fuel percolation problem.

 

thanks for all the help


my car has one of those fans for the carb that you are talking about but i thought i heard someone state that it doesnt help so i unhooked it last year...i'll b sure to hook that back up now and try to do some sheilding for my fuel lines...thanks!

 

Post a pic of that fan, I have never seen one.

 

Me too, I've never heard of that!

Pic please.

 

That fan was a dealer-installed item, installed as a "campaign", IIRC. I've seen them in some other vehicles, especially inline 6-cyls where the carb sits literally right on top of the exhaust manifold. A friend of mine has a Toyota Land Cruiser that has one for example.

It won't do a lick of good when the car is moving. Its only puropse is to help heat soak when the car is sitting still.

Same thing with vapor lock at WOT. Think about fuel flow for a minute.... when you're at WOT, the fuel is flowing fast; that means there's a continuous supply of cool fuel from the tank; that means that the tendency toward vapor lock is minimal.

If your problem was at its worst right after idling or heat-soaking for a while (like Marc's description), and it didn't do it on a cool night or whatever, then it might be vapor lock.

Also, more often than not, what really happens with hot fuel, is not vapor lock. Rather, the fuel is liquid in the fuel lines, but after it passes through the needle valve and its pressure drops suddenly from 4 psi to atmospheric, it boils violently, and spews out of every hole in the carb. But again, this isn't an issue in the middle of a WOT blast, it happens after the car gets driven, turned off and parked, and started up after 5 or 10 minutes. Mine used to do it when I'd go to the store or something; runs fine on the way to the store, park it, go inside and do my thing, come back out and crank it up, and it would run for just long enough to pull out into the middle of the street, and then die. Then it would crank and crank and crank and crank, and when it finally did start back up, blow an enormous cloud of black (rich) smoke until it got cool fuel again. Turned out, the fuel pump had no gasket, only silicone, where it met the block; putting a gasket there helped immensely, and putting a second one there cured it completely. But that doesn't sound like your problem.

You have a fuel delivery problem. All the rest of that is irrelvant to your issue.

 

pic 1 is a pic of the blower...if you cannot tell...it is located in the fenderwell right next to the battery.......


pic 2 is the routing of the hose......



and pic 3 is where it blows onto the fuel line and carb....

 

pic2

 

pic3

 

RB83L69....well i replaced the fuel filter last year...i will replace it again since its easy and cheap to do....and then i guess i will just go from there....thanks for the info

 

Wow, what an octopus of vacuum hoses and emissions gear. No wonder the carb needs cool air blown on it, there's no air movement under that hood!

My only vacuum lines are to the distributor, brake booster and PCV valve, I feel lucky now.

 

RB,

While you are 99% right as usual. I do belive that the fuel starvation issue that is being experienced could be due to heat in the fuel lines, especially if the vechicle has headers. Hell, you know how close headers get to the fuel line, (touching). What's worse is most early thirdgen gas tanks had small heat shields. Those shields coupled with large 3"exhaust makes the fuel tank get very very hot. I know this from personal experience. My tank would get hot to the touch before the updated sheilds were installed and my factory fuel line would burn my hand, literally. Before the shields and rerouting the fuel line to the drivers side I always had a second gear surge. Now, that is eliminated on all but a really hot day.

Speaking of pressure drops:

Electrical fuel pumps help alot but can be a pain also because of the pressure drop in the regulator causing fuel flash. Not near as bad as the vacuum created by a mechanical pump though.

 

well i replaced the fuel filter today and the car didnt surge anymore but it still doesnt feel like it pulls like it used to....b4 it would feel like a 2nd round of hp when the 2ndaries(yep im lazy) would open up and my car would really fly....now its all gradual and doesnt feel like it pulls as hard....maybe it was just a fluke when my car ran a 14.7

 

ok well i was just browsing some of the other reacent carb posts and i guess that stock replacement choke pull offs have too small of holes which causes the secondaries to not open so fast......so that may be what the diff is....now to do a search on what size to drill it out to cuz im sure there is a pinnacle point where one shouldnt cross with the diameter...and with my luck i would cross it and the carb would bog cuz the secondaries would open too fast.... .....

 

Silly Matt,

There is a screw on Quadra-Jet carbs for adjusting secondary opening rate.

 

lol

yah i messed with that before and got it to where i like it...but i thought that the tensioning screw and the pull off both regulated how fast the secondaries opened?