I am driving an 86 IROC with a 305 LG4 with a T5 setup.

The engine was rebuilt with the L69 camshaft and also the exhaust has been upgraded to a 3" catback with a flowmaster muffler. The computer controlled Qjet has also been rebuilt and is a stock setup.

The ECM was replaced with a newer 1228079 ECM out of an 87-88 Monte Carlo SS and we are using the monte carlo SS automatic chip as well.

The engine will rev happily very high, 1st and 2nd gear seem to have power and when you shift into 3rd gear it falls flat on its face. It backfires and bogs and acts as if its run out of gas with no power at all. Shifting into 4th at that point gives you basically the same thing and eventually the power will come back in enough for you to get out of the way and get into 5th gear to cruise.

Part throttle shifts seem to be fine.

When I crack the throttle open all the way and peek inside the air doors, the secondary valves are not opening inside the carb.

With the car in neutral running at idle and with the air cleaner off, the carb is very responsive when you apply the throttle manually at the carb.

The secondary air doors do not open at WOT but is that because there's no load on the engine when not in gear? The vacuum brake seems to keep the air doors closed while the engine is running.

The other cars I have all have Tuned Ports so I really am at a loss when it comes to Qjets.

 

That would be a fuel delivery problem... the fuel system can't keep the bowl full when the engine has a sustained high fuel demand. Something somewhere is restricted.

Replace the fuel filter first.

 

A friend of mine gave me an old Qjet off an 84 L69 high output engine and I removed the secondary hangar and it has a set of DR secondary metering rods.

I just removed the stock hangar and its got CH rods in there.

I swapped the CH rods for the DR rods and test drove it. Its running much smoother now, no bogs. The ambient temperature is also much cooler now than it was earlier today.

It cant be THAT easy can it, just swapping rods?

 

Yes sometimes it can be. There is also an article here:

https://www.thirdgen.org/quadrajet

that will walk you through fine tuning your secondary air valve tension.

 

Car is very happy with the DR rods.

The only thing I am going to mess with is the choke because its running too lean at startup and dies out sometimes.

I am going to use this page to see if there is another set that might be fun to try:

https://www.thirdgen.org/rods

 

I ran into the same problem yesterday, it was really hot, over 100 outside. The car was getting over 220 and thats when I started to feel the cutting out in 3rd and 4th. I was running the A/C and turned it off to see how the performance would be and it was terrible.

I bought a new fuel filter today and am going to install it when the engine cools down.

 

I just replaced my old O hangar and CH rods. Got some new DR rods from the dealership which they had to track down somewhere in the mid west. Also replaced the G hangar with an Edlebrock brand unit. So far so good. Keeping the original hangar and rods just in case.

 

Fuel filter might help, but the real problem is VAPOR LOCK....The factory L69 cars had a huge problem with this, as did my LE9 305 Van. Too much heat around the fuel pump would cause a vapor lock situation. My van (300 hp 355 at the time) did it so bad pulling a trailer into the mountains on a 105*F day that it, started bucking badly, and then just stalled, would not start until it cooled down again.

My suggestion is use an in-tank fuel pump sending unit from a TBI car, upgrade the fuel pump to a TPI pump while it is out, and plumb the system for a bypass style regulator. You will spend a good $300.00 to set it up properly, but you will never vapor lock. I upgraded my whole fuel system to a 1992 TBI Van setup minus the TBI and it worked well. It also served basis for a later swap to TBI and yet another swap to TPI.

We did this on my brothers 80 Chevy truck.

Also a 1" aluminum spacer will help keep the heat out of the carb and make hot restarts easier.

 

Just a tip, many fullsize vans had the DR rods and F hangers STOCK and many Cadillacs/Oldsomobiles/Buicks and Station Wagons with the 307 had F hangers. DR rods + F hanger is a match made in Q-Jet performance heaven.

 

I put the new fuel filter in and it helped a bit, it feels slightly more peppy. I knew it probably wasnt the fuel filter already.

Its definitely heat related, it only happens when the engine temp goes over 220 degrees.

I am currently looking for dual fan radiator mounts to mount the extra set of dual fans I have in the garage. I also think this car could benefit from a dual snorkel intake, so I am going to hit the junkyard and make one.

 

How do I start a new thread...I'm new to thirdgen and I have a fuel system problem on my 89 5.0 bird.thanks,