Hesitation on a 307

[jschunke]

Is there anyone that remembers the carbureted 307?

It hesitates badly at a certain throttle position - just

a little above idle. Give it more throttle and it takes off.

It idles fine. Thanks.

[Scotty]

Is there anyone that remembers the carbureted 307?

It hesitates badly at a certain throttle position - just

a little above idle. Give it more throttle and it takes off.

It idles fine. Thanks.

It's the accelerator pump in the carburator. There is a leather and sometimes rubber 'seal' that gets deformed and you don't get a good shot of gas on takoff and you bog, simply replace the accelerator pump and you will be good to go. You can buy a carb rebuilding kit and it will be included along with a new needle valve and seat, gaskets, etc. The diagram below is of a Rochester 2bbl carb, there is a good possibility that you have this carb. See #43 below, I circled the pump assembly, I have rebuilt many of these.... If you have a 4bbl let me know I probably have the schematic (I knew this stuff would come in handy one day! )

[Scotty]

Here is the numeric key

[OynxSTS]

Is there anyone that remembers the carbureted 307?

Scotty is bang on with the accelerator pump.

I'm guessing that since you are in a Caddy Discussion Board your 307 is an Olds. I have one in my 442 and 90% of the engine problems you will have with these engines, even the CCC ones from the late 80's, can be cured with a Carb rebuild kit and a couple of can's of Carb cleaner. I thought most of the Olds 307s that came in Caddies we Fuel Injected...

In any event most of the Olds 307 that were carbureted were Quadrajets and were usually Computer Command Control ones... Chevy 307s... Now there’s a dog of a motor, they were almost all 2 barrels.

Anyway back to your problem, to get to the accelerator pump you are going to have to take the top horn off of the carb... My advice... take the whole carb off of the car (reduces the risk of dropping one of the tiny screws or pins down the intake) and rebuild the whole thing... Take care to blow carb cleaner through all of the little passageways. These gum up and will cause off idle misses/stumbles/hesitations too.

Trust me, you will be amazed at the difference! Your car will drive like new!

Oh ya, if it is a CCC Carb, Replace and adjust the throttle position sensor too. Use only a AC Delco replacement sensor. Contrary to popular belief, these units do not last for ever…and the aftermarket sensors are total crap.

[Scotty]

Ahh, my favorite carb, the Quadrajet...in case you have a 4bbl....

[jschunke]

It's an '84 Olds, 4bbl with CCC. Accellerator pump

makes sense, but I just rebuilt the carb a few months

ago. Crap, I've gotta take it apart again!

[OynxSTS]

It's an '84 Olds, 4bbl with CCC.  Accellerator pump

makes sense, but I just rebuilt the carb a few months

ago. Crap, I've gotta take it apart again!

Just a second,

Before you take it apart... again... Back probe the TPS...My CCC book is at home, I bet Mike knows the number from memory… But at idle you should get something like .95 of a volt… with the voltage gradually and evenly increasing as you open the throttle.

First check that the idle setting is right… This is the first and easies thing to fix, you can do it with the carb on the car and without disassembling the top half again. If the voltage change is uneven then you have a bad TPS…

One last question… did you replace and/or fiddle with the float? A poorly adjusted float can also cause hesitations due to fuel starvation. Unfortunately, as you know, to replace the float you are going to be spreading carb guts all over your coffee table again…

[JasonA]

Another thing to check is the EGR valve and EGR ports in the intake manifold. These ports clog rather frequently, and can cause a lean condition. I had a similar condition on mine that turned out to be a bad EGR valve. It was the original on my ol' 1984 Cutlass with the 307. Look here for more information on the EGR condition:

http://tech.oldsgmail.com/307_egr.html

[Scotty]

You know its funny you bring this up, I worked on my friends Chevy Caprice to get rid of a bog and was never able to clear it up. It was the most frustrating automotive experience I ever had. It acted like an accelerator pump in the carb, and I do believe I cleaned the EGR.... I'll bet it was a bad EGR valve

[jndnaps]

My 87 442 was doing the same thing. I just had the carb rebuilt. I'll pick it up Monday and see how it rides now. I'm the original owner and the car has 79K on it and this is it's first carb rebuild. Still has the original exhaust on it.. Gonna put some Flowmasters on it in a couple of weeks..

[Scotty]

My 87 442 was doing the same thing. I just had the carb rebuilt. I'll pick it up Monday and see how it rides now. I'm the original owner and the car has 79K on it and this is it's first carb rebuild. Still has the original exhaust on it.. Gonna put some Flowmasters on it in a couple of weeks..

Very Nice car, you have kept it in great condition. Is it garaged?

[OynxSTS]

My 87 442 was doing the same thing.

We are hopelessly off topic here, but your '87 442 is in much better shape than mine... Let just say that I got this car "used"

[jndnaps]

Thanks.. Yes, it's always garaged.. I keep it at my mothers house in her garage. I don't have room for it at my house. I don't really drive it that much. I like to drive it during the cool Florida winters. It's the first and only brand new car I ever had. I sat down with the Olds salesman at King Oldsmobile in Croton NY and ordered it.. That's my baby..

[jschunke]

I'd show my black beauty but wouldn't want

to nauseate anyone. There are two error codes:

24 - vss - a fault in vehicle speed sensor and

34 - MAP - signal from MAP sensor too high.

Had code 24 for years. Any idea where the VSS

is located? Code 34 is new, so maybe that's the

culperate. It has had a strange idle since rebuilding

the carb. It chuggs kinda like Christine.

[JasonA]

I'd show my black beauty but wouldn't want

to nauseate anyone.  There are two error codes:

24 - vss - a fault in vehicle speed sensor and

34 - MAP - signal from MAP sensor too high.

Had code 24 for years. Any idea where the VSS

is located? Code 34 is new, so maybe that's the

culperate. It has had a strange idle since rebuilding

the carb. It chuggs kinda like Christine.

The VSS is actually on the back of the speedometer head, on 1984 and later vehicles. The MAP sensor, on my old Cutlass, was located on the passenger side wheel house.

Here's a picture of my beloved. I sure do miss her.

http://jadcock.oldsgmail.com/cutlass/

[jschunke]

Thanks Jason, that helped me find the problem.

The air injection tube sprung a huge leak and

singed the MAP sensor vacuum line. Who knows

what else got fried. Now I have to replace those

injector tubes. What if I plug the exhaust ports

and forget about air injection? I'm also a Virginia

grad, Biomed UVa 1987

[OynxSTS]

From what I have read, it is OK to remove and plug the AIR system and I plan to do exactly this on my 442.

The air injection system does cause a slight drag on the engine but again from all I’ve read this is not much more that a single HP.. If that…

The air injection is only supposed to work when the engine is cold and is running “open loop” i.e. the Oxygen sensor is being ignored by the computer. Its purpose is to help burn off (and help the Cat burn off) extra fuel from the “rich” start up cycle.

Most engineers will recommend NOT removing functioning systems on newer cars as it does reduce emissions and is suppose to help extend the life of the Catalytic converter(s). Plus in many States/Provinces removal of the system is illegal.

However these systems do fail in older cars and can cause the computer to do all kinds of odd stuff as the extra oxygen in the exhaust stream makes the O2 sensor go nuts.

Also for what its worth, GM did build lots of Q-Jet cars in Canada without AIR pumps as our emission laws (in the early 80’s anyway) were a little behind the US. As far as I can tell GM used the same Cats in Canadian and US cars with little difference in longevity…

The other way these fail on the Olds V8s is the check valves that prevent exhaust gas from flowing into the system fail and the hot exhaust melts all of the upstream plastic bits...

To make a long story short:

If its working, leave it alone...

If its failed, remove and do not repace it...

Kinda like an apendix...

[jschunke]

What are you going to use to plug the

exhaust ports? Screw in some stainless

steel bolts? If I do recall there are some

tubes that extend from the ports into the

heads. They may get in the way, no?.

[JasonA]

Yes, you can dismantle the A.I.R. system, although it will in theory increase your tailpipe emissions. As stated above the A.I.R. (Air Injection Reaction) pump only takes 1 hp to run, if that. You won't notice a difference at all after you remove it.

I do believe the Canadian 307s didn't have the bosses drilled for the A.I.R. system. Here's a page for some more reference on the 307 heads:

http://tech.oldsgmail.com/307_heads.html

The system basically consists of three "pipes" if I recall correctly. One pipe going to each head (which splits off to a 4-tube manifold), and one pipe going down to the catalytic converter. There's a diverter valve which, again, if I recall correctly, pushes air to the heads, to the converter, or "releases" it to the air cleaner housing.

If you remove the A.I.R. manifolds that run to the heads, you'll have to plug the holes, yes. You should be able to find very shallow threaded plugs. You're correct -- there are 1.5" long tubes that extend down into the exhaust valve area from where the threaded ports are, and I don't know how they would interfere with a long screw plug. I'd try to find some of those shallow plugs. I've seen them in brass, but I don't think brass would be the material of choice here. Usually, these things are rust-welded to the heads and you don't get them off. What I would suggest is capping the tops of the A.I.R. manifolds with a rubber plug. I would leave the check valve in place (to prevent hot gasses from melting your rubber caps), and install the cap on the check valve. I've seen plenty of vehicles with this. These A.I.R. systems were very common on GM vehicles of all kinds in the 1980s.

I left mine intact for originality purposes, since I was competing in car shows with it often. Even if I wasn't, I would have left it in place unless something went really wrong with it. The simplicity of not having the system there at all is appealing, although emission levels would rise probably. I installed an Olds 403 engine into an '87 Regal which originally had a 307 (and an A.I.R. pump) and didn't reinstall any of that system. The 403's heads didn't even have the bosses drilled for the A.I.R. manifolds if I recall correctly, so I didn't use them. I didn't use the computer either. I got a non-CCC Q-jet carburetor and a diesel version of the right-side exhaust manifold, which didn't have the hole drilled for the O2 sensor. In my case, I needed new exhaust manifolds anyway because the puny '87 stainless steel "log" manifolds didn't mate up to the 403's larger exhaust ports. A buddy of mine had a junked Caprice with a diesel Olds 350 that he gave me the exhaust manifolds from.

[jschunke]

She must've been running lean. There's a mixture adjustment

screw inside the carb that is accessed from the front top. It was

screwed all the way down. Two turns out and no more hesitation.