[FrankieSixxxgun]

Alright, we've been chatting it up in the gas mileage thread about my weirdo fuel delivery problems, so I figured I'd start a new thread to kinda keep the other post on topic. Here are my symptoms thus far:

- Car runs awesome cold. The power I'd expect from the 307 is there and it's pretty responsive for a 200k (I think, the odo says 98k and it's probably rolled once before) mile old ass car.

- Once the car warms up, I get knock when slightly on the throttle.

- Once warm, but not every time it's warm, the car has no power past 1/8 push on the accelerator. If open more than 1/8, the car will actually slow down. It feels like it's choking out on A/F mix, but I can't tell if it's rich or lean.

- At idle, when warm, I hear a slight, fast-pased chirping from the engine compartment somewhere. Possibly a vaccum line or maybe bad EGR?

- Last tank my mileage was around 14.5 MPG. Definitely low for a FWB, right?

- The car seems to run hot. I don't know if that's just 80's emissions and a 195 t-stat doing it or if there's actually a problem. I know the modern cars run hot for fuel efficiency, so I'm probably used to my cold-running 60's and 70's engines.

Now for diagnosis/troubleshooting:

- Replaced the O2 sensor. According to the service manual procedure, the original one from 1987 in my car was dead. I figured it's probably worth the $15 to replace something that should be serviced every 15-30k.

- Checked the EGR. I can press the valve freely with my hands and it will stumble and stall the engine.

- Timing is set, with the diag grounded, to 20* BTDC per the under-hood instructions.

- Idle is set per the under-hood instructions.

- Rebuilt the carb with a kit from Advance auto. I'm no carb master, but I'm pretty sure I got all the parts back where they belong (Q-Jets are complicated when compared to motorcycle carbs!). The plugs are still out since I've been playing with the adjustment screws.

- Set the dwell to run at 30* +/- 5 with the idle air ajustment screw.

- Fiddled with the float stop screw, probably bollocks'd it all up.

- A/F idle mix screws set at default per the rebuild kit directions.

I love driving this car when it's cold, but sometimes when it's warm, I can't even maintain 65mph on the interstate. Forget about trying to go when the A/C is on too, the compressor just pulls the engine to a halt. Sometimes I gotta stand on the pedal just to get the car out of its own way. Help!

 

[Kev]

First - Check all of your vacuum lines and replace any that are cracked, checked or questionable.

Second - Your engine should run at around 200 degrees when warmed up, if it it running substantially higher check your cooling system.

Third - Double check your float adjustment.

Fourth - Check your EGR by sucking on the vacuum line connected to the valve, if the diaphram is intact it should stall the engine as thought you were pushing on it by hand. If it doesn't, chances are the diaphram is punctured and the valve should be replaced.

Fifth - Double check your choke assembly, make sure it is properly adjusted.

 

[BluEyes]

Have you checked for engine codes? Not all codes light the SES light.
Being a feedback carb, you should still be OBDI, so you can get a code "reader" from Walmart for $20 or 30. Or, if you have a chiltons manual, I believe they tell you which two ports on the diagnostic connector to jumper together and also includes a list of diagnostic codes.

 

[FrankieSixxxgun]

I have a code reader that someone gave me. Last time I checked the codes I was getting a MAP error and a rich condition. That was from my dumbass leaving a vacuum line unplugged. There are no current codes.

 

[N0DIH]

What, if any, codes set?

- Once the car warms up, I get knock when slightly on the throttle.

typically normal if no knock sensor is present or working. But could indicate lean condition.

- Once warm, but not every time it's warm, the car has no power past 1/8 push on the accelerator. If open more than 1/8, the car will actually slow down. It feels like it's choking out on A/F mix, but I can't tell if it's rich or lean.

Sounds like it is lean, is M/C solenoid stuck down? Float level set wrong? Vacuum port open at cruise? PCV stuck open? Cracked vacuum hose? PCV is common to crack when old. Power Brake vacuum line cracked? Is EFE stuck in middle or close position?

- At idle, when warm, I hear a slight, fast-pased chirping from the engine compartment somewhere. Possibly a vaccum line or maybe bad EGR?

Look for AIR pump making noise or leaking (pumps like to chirp), choke tube into intake leaking? air mainfolds leaking (common)? Exhaust manifold leak (not common)

- Last tank my mileage was around 14.5 MPG. Definitely low for a FWB, right?

Yup, that is low, my LT1 in -5 degree F weather is DOWN to 16.7 city with me being a little punchy on the throttle. AND 3.42 gears (factory towing package)

- The car seems to run hot. I don't know if that's just 80's emissions and a 195 t-stat doing it or if there's actually a problem. I know the modern cars run hot for fuel efficiency, so I'm probably used to my cold-running 60's and 70's engines.

EFE valve stuck will make it hot and ping. Low timing will make it run warm (which is a "normal" process during cold start to rapidly warm the converter up), is it getting into closed loop? You won't get lockup in open loop, but after 3.5 minutes exactly from a cold start, you get lockup. Eng temp below 140F might delay or prevent this. But 150+F won't.

 

[FrankieSixxxgun]

What, if any, codes set?

None.

typically normal if no knock sensor is present or working. But could indicatelean condition.

I didn't know I had a knock sensor on the 307. I didn't see one when I was playing when I had the exhaust off the car. Is it somewhere else?

Sounds like it is lean, is M/C solenoid stuck down? Float level set wrong? Vacuum port open at cruise? PCV stuck open? Cracked vacuum hose? PCV is common to crack when old. Power Brake vacuum line cracked? Is EFE stuck in middle or close position?

Not sure. Float was set to spec during rebuild, but the float stop screw is probably all out of whack. There could be a vacuum port open, beats me. I think I just replaced the PCV, but I can't remember. I know I did every other little filter, so I'd imagine I remembered to do the PCV. Stock hoses, so something could be cracked. I need to get in there with some starter fluid and see if I can find a leak. The EFE doesn't seem to be a problem. I disconnected it and the car ran exactly the same, so I just hooked it back up.

Look for AIR pump making noise or leaking (pumps like to chirp), choke tube into intake leaking? air mainfolds leaking (common)? Exhaust manifold leak (not common)

Could be the pump. The chirping is only when I'm off-throttle. Any throttle at all and it goes away. The air manifolds are the little tubes that screw into the heads, right? I checked 'em all and they're tight, but who knows. The exhaust is totally redone with all new gaskets, lockwashers, and locktite. It ain't leakin'!

Yup, that is low, my LT1 in -5 degree F weather is DOWN to 16.7 city with me being a little punchy on the throttle. AND 3.42 gears (factory towing package)

Yeah, my mileage blows. I'd love to see the advertised 17 stop and go.

EFE valve stuck will make it hot and ping. Low timing will make it run warm (which is a "normal" process during cold start to rapidly warm the converter up), is it getting into closed loop? You won't get lockup in open loop, but after 3.5 minutes exactly from a cold start, you get lockup. Eng temp below 140F might delay or prevent this. But 150+F won't.

How can I be certain it's in closed loop? I mean, the car noticibly changes behavior when it warms up. I've done the carb adjustment on the idle air screw and the dwell meter did adjust itself +/- 5 degrees, so that means I hit closed loop, right?

 

[N0DIH]

Easiest way to determine closed loop is if the TCC locks, it won't in open loop. I think there is a mode with a resistor in the ALDL that will tell more, but I have to look it up. Depending on what is in between A and B on ALDL does different diagnostic modes.

EFE's get physically stuck, you have to follow it down and watch it move with vacuum applied and then not. The 307 does well with it operating, however it can be removed, but the exhaust pipe gets awful close to the starter, and starter life is reduced, and 455 starts no longer fit.

Not sure what you mean on float stop screw. There isn't on any any Q-Jet I have ever seen (and I have a bunch, as well as opened a lot of them to pirate parts in the boneyard). There is the seat, the needle, the float, the pin and the itty bitty hangar that hooks the needle onto the float end. Nothing should ever touch the float except those things and fuel.

http://members.optushome.com.au/ozfbody/info/q_jet/Carb_overview.html Take a look here and see if you see it.

 

[johndfw]

Hey Frankie.
I dont know if you've read this before or not, but I found it very helpful when rebuilding my Q-jet a couple of weeks ago. You might look at tips #3 and 4.
Hope this helps.
http://www.florida4x4.com/tech/quadrajet/qtune.pdf

 

[FrankieSixxxgun]

Easiest way to determine closed loop is if the TCC locks, it won't in open loop. I think there is a mode with a resistor in the ALDL that will tell more, but I have to look it up. Depending on what is in between A and B on ALDL does different diagnostic modes.

EFE's get physically stuck, you have to follow it down and watch it move with vacuum applied and then not. The 307 does well with it operating, however it can be removed, but the exhaust pipe gets awful close to the starter, and starter life is reduced, and 455 starts no longer fit.

Not sure what you mean on float stop screw. There isn't on any any Q-Jet I have ever seen (and I have a bunch, as well as opened a lot of them to pirate parts in the boneyard). There is the seat, the needle, the float, the pin and the itty bitty hangar that hooks the needle onto the float end. Nothing should ever touch the float except those things and fuel.

http://members.optushome.com.au/ozfbody/info/q_jet/Carb_overview.html Take a look here and see if you see it.

I never looked at the EFE with the car on, but it looks like the default position of the EFE on the 307 is open. I just had the entire thing off the car and looked at it in detail since it's one of the most bizarre things I've ever seen.

There are 5 adjustments on the Q-Jet that I'm aware of. There are the two idle mix adjustment screws on the front of the carb, then at the top in the air horn there are the TPS adjustment, there's a flathead screw that adjusts the idle air bleed, and then just slightly more towards the front is a screw labeled float stop screw according to any diagram I've ever seen. Due to it's location, it looks like the farther down you screw it, the more it bumps up against the float. Maybe it butts up against the needle thing, who knows, but it's there under some plug.

The car makes it into lockup (and randomly back out), so it's getting into closed loop then?

 

[FrankieSixxxgun]

Hey Frankie.
I dont know if you've read this before or not, but I found it very helpful when rebuilding my Q-jet a couple of weeks ago. You might look at tips #3 and 4.
Hope this helps.
http://www.florida4x4.com/tech/quadrajet/qtune.pdf

Man, that document kicks ass! Thank you!

 

[johndfw]

Frankie....
Any luck?

 

[FrankieSixxxgun]

Haven't had a chance. I've been grounded with this strep throat that's going around or something. I'm lucky to even make it into work, let alone to play around with my toys.

 

[johndfw]

Sorry to hear that. Hope you get better soon.

Cheers!

 

[carnut]

Have a muffler shop check for a restricted Cat. converter or simply unbolt the front of the converter, pull it down reinstall two bolts to hold it disconnected and drive the car. Will be very! noisy but should help determine if power is restored. If the material within the converter is loose it will plug up the exit after driven and cause noticable power loss. Sounds to me like you are knowledgeable regarding your carb and its adjustments. The slight ping and bogging when throttle is depressed sounds like restricted exhaust. Hope this helps, Bill.

 

[FrankieSixxxgun]

Have a muffler shop check for a restricted Cat. converter or simply unbolt the front of the converter, pull it down reinstall two bolts to hold it disconnected and drive the car. Will be very! noisy but should help determine if power is restored. If the material within the converter is loose it will plug up the exit after driven and cause noticable power loss. Sounds to me like you are knowledgeable regarding your carb and its adjustments. The slight ping and bogging when throttle is depressed sounds like restricted exhaust. Hope this helps, Bill.

I've had a car with a clogged exhaust before and it always ran like crap. The car runs good sometimes, bad others. It's probably vacuum or sensor related.

I redid the exhaust on the car and, in tradition of being white trash, ran the car open-cat for a little bit just to annoy my neighbors. Although weak sounding, it seemed to flow fine. There's a steady, strong stream out of the exhaust pipe at idle too. On the other car where the exhaust was clogged, you couldn't feel anything coming from the pipe.