engine and drivetrain Car Bogging Troubleshooting (Stumped!)

[Utah02]

I think Toby might be on to something here; which coil do you have and how is it's condition?

I have a Bosch black coil (I think) but I have used a Bosch blue coil in perfect condition with no luck.

[zinz]

In other words, if ive eased of the pedal about a centimeter, I can accelerate as much as the car will.

 

This has perplexed me for a couple of days... Are you saying that if you ease off the accelerator just a bit, the engine will accelerate to redline without bogging? 

 

Ed

[Utah02]

This has perplexed me for a couple of days... Are you saying that if you ease off the accelerator just a bit, the engine will accelerate to redline without bogging? 

 

Ed

Yes sir. I too am confused by it. This is a total shot in the dark but I don't have carpet in the car right now. I'm on bare floor pans. I just ordered carpet. Once it's in, maybe that cm will be taken up by the carpet thickness and the bogging won't be able to happen. I know there is about a 5% chance of that but just a thought.

[Russell74Fjord]

I would  check all the fuel filters, one at the bottom of the sender unit, one in line, one at the carb fuel inlet, one perhaps in the fuel pump, to make sure there is sufficient fuel delivery.

 

Pertronix, so no condenser, otherwise that can be suspect.

 

It sounds like you are running out of gas, - could be a mixture issue,

[PaulTWinterton]

Have you checked your filters yet? You might be getting bogged down  with theories when it's simple fuel delivery.  Also, one of the easiest details to check.

 

Carpet's a long shot.

Edited May 16, 2015 by PaulTWinterton

[Chris_B]

I read your posts, so excuse me if I missed this. Have you checked your fuel pressure? One interesting test if you could leave a gauge installed would be to pull over to a save place right when the bogging i occurring, shut off the motor and observe the fuel pressure.

 

Also, have you done basic troubleshooting, like compression test, charging system test, etc. For example, if you don't have sufficient power, your ignition system will not be able to sustain itself at higher revs.

[jgerock]

I'm with Chris B.  Check the pressure and also the volume of fuel. If your car is an original carbureted 2002, double check the fuel outlet from the tank.

[zinz]

Ok. hmmmm... My thought was the throttle butterflies are being opened past center and thus "closing" somewhat. This is possible on some carbs (like my Solex DDHs) but they only over-rotate slightly, certainly not a great deal. Perhaps you can double check the linkage at the carburetor by looking down the throat while actuating the linkage by hand (or someone in the driver's seat).

Another thought was that you have an electric fuel pump? Do you have a pressure regulator? when your car is "bogging" is it blowing a lot of black smoke? Might be over-fueling from too high a fuel pressure?

I'm with Paul and others that you check the filters first...

Certainly perplexing that you get normal acceleration when you lift slightly... Seems like a linkage issue, too. Interesting...

Ed

[Chris_B]

Here are a few other thoughts. You said you changed your spark plugs. How did they look?  Another test you can perform is to (again, driving the car at a safe place) accelerate until you get to the bog point, then coast to a safe pull-out and shut off your motor ASAP. Pull a couple of plugs and observe the condition. Grey and dry suggests a too lean condition; covered with black, fluffy soot suggests a too rich condition. 

 

Pumping in "too much fuel" will not cause the car to choke and pop. These typically are symptoms of a too lean condition. The mixture question is vexing, because the symptoms can be similar. In my experience, a hyper-rich can cause the motor to cut out entirely, whereas a too lean mixture will cause popping and can also cause the motor to loose power. But, you said you swapped the carbs. How strange that this condition followed your carb change... I guess a fuel supply problem (too rich or too lean) could do that. Or it could be something else- again, have you checked your electrical system (s/b >+14.4V at ~1000 rpm when checked at the battery)?

[Utah02]

Here are a few other thoughts. You said you changed your spark plugs. How did they look?  Another test you can perform is to (again, driving the car at a safe place) accelerate until you get to the bog point, then coast to a safe pull-out and shut off your motor ASAP. Pull a couple of plugs and observe the condition. Grey and dry suggests a too lean condition; covered with black, fluffy soot suggests a too rich condition. 

 

Pumping in "too much fuel" will not cause the car to choke and pop. These typically are symptoms of a too lean condition. The mixture question is vexing, because the symptoms can be similar. In my experience, a hyper-rich can cause the motor to cut out entirely, whereas a too lean mixture will cause popping and can also cause the motor to loose power. But, you said you swapped the carbs. How strange that this condition followed your carb change... I guess a fuel supply problem (too rich or too lean) could do that. Or it could be something else- again, have you checked your electrical system (s/b >+14.4V at ~1000 rpm when checked at the battery)?

I'm checking the electrical system later today. To me it still seems like a fuel starvation problem. I'm also going to check the fuel filter in the tank today. I'll let you guys know.

Thanks

Utah02

[percy]

 

1972 carbed 2002.

bogging problem.

car wont accelerate past 4000 rpms in ANY gear if I'm pedal to the metal.

If ive eased of the pedal about a centimeter, I can accelerate as much as the car will. If I'm pedal to the floor, anywhere from about 3,500 to 4,000 rpms the car will just cut power. It will hit those rpms and then drop down 500 or so rpms then wont accelerate. It makes a backfiring/bogging noise too. So here is the list of our ideas and attempts to fix it:

 

1. Changed the spark plugs, no fix.

2.  Simple timing issue. Timed the car, no fix.

3. 38/38 carb was too much. switched to weber 32/36 carb, no fix.

4. Tune carb. No fix

5. Pertronix was bad? switched back to points, no fix.

6. Bad distributor all together? Switched to a good one, no fix.

 

took the car for one more drive. In first gear it went up to 6000 rpms and then the car made a loud POP. The fuel pump just shut off, car died. 

 

 

 

Perhaps your car is telling you it would prefer a different name? 

 

6000 in first gear, a loud POP and the fuel pump shut off?

 

With all of the information you provided you fail to disclose how long this situation has persisted.  Is this phenomenon something new?   But for your 6000 rpm detail I too leaned toward Toby's rev-limited rotor theory.  Max engine speed can also be controlled by sophisticated aftermarket electronic ignitions (which you evidently do not have) and a weak, degraded or otherwise compromised ignition system, including the cap and rotor and reversed coil polarity.

 

A uniformly worn cam or maladjusted cam timing can restrict high speed engine operation.  When was the last time you checked your valve lash?  Valves that don't fully open may permit a nice smooth idle but might also restrict high speed breathing.   Are you running a non-stock cam and/or do you use a cam shaft with an adjustable cam gear?  Another long-shot, compression?

 

What was the POP, and what really caused the fuel pump to shut off?  What pump are you using and how is it wired?  A fuel restriction might cause a pump to overheat and there might be some overload protection.  And yes, literally running out of fuel might create a lean condition ripe for intake backfire. Too much fuel in the intake manifold and an intermittent ignition  -  could also cause backfire on the southern end of the engine, i.e., muffler.   How do you know the pump quit?  Is it fused with a relay?

 

The fact that you changed carburetors should eliminate most questions regarding throttle plate operation and probably linkage issues.  (What are the odds both carbs suffer from the same throttle plate orientation issues?)  But - it might be interesting if you described any differences in engine operation between the two carburetor installations.  Different carbs with different (unknown) jetting might yield different fuel delivery situations and different symptoms  - at different throttle positions and engine speeds and loads.   

 

While I am inclined to agree with others regarding fuel supply issues, mention of an electronic fuel pump and coils raises possilble electrical issues, including a possible short caused or exacerbated by vibrations at higher engine speeds under load.  The fact that reducing the throttle pedal depression by a centimeter restores power suggests even the possibility that the throttle linkage is touching or otherwise affecting the ignition and/or voltage supply to the fuel pump.  I would expect that if you have one or two of the 12v pigtails (originally intended for the solex) poorly secured or insulated this might result in a short and a blown fuse  -  but I suppose there are other possible consequences, depending upon what you might be doing with those wires.

 

Pictures, pictures and pictures?

Edited May 21, 2015 by percy

[Utah02]

Perhaps your car is telling you it would prefer a different name?

6000 in first gear, a loud POP and the fuel pump shut off?

With all of the information you provided you fail to disclose how long this situation has persisted. Is this phenomenon something new? But for your 6000 rpm detail I too leaned toward Toby's rev-limited rotor theory. Max engine speed can also be controlled by sophisticated aftermarket electronic ignitions (which you evidently do not have) and a weak, degraded or otherwise compromised ignition system, including the cap and rotor and reversed coil polarity.

A uniformly worn cam or maladjusted cam timing can restrict high speed engine operation. When was the last time you checked your valve lash? Valves that don't fully open may permit a nice smooth idle but might also restrict high speed breathing. Are you running a non-stock cam and/or do you use a cam shaft with an adjustable cam gear? Another long-shot, compression?

What was the POP, and what really caused the fuel pump to shut off? What pump are you using and how is it wired? A fuel restriction might cause a pump to overheat and there might be some overload protection. And yes, literally running out of fuel might create a lean condition ripe for intake backfire. Too much fuel in the intake manifold and an intermittent ignition - could also cause backfire on the southern end of the engine, i.e., muffler. How do you know the pump quit? Is it fused with a relay?

The fact that you changed carburetors should eliminate most questions regarding throttle plate operation and probably linkage issues. (What are the odds both carbs suffer from the same throttle plate orientation issues?) But - it might be interesting if you described any differences in engine operation between the two carburetor installations. Different carbs with different (unknown) jetting might yield different fuel delivery situations and different symptoms - at different throttle positions and engine speeds and loads.

While I am inclined to agree with others regarding fuel supply issues, mention of an electronic fuel pump and coils raises possilble electrical issues, including a possible short caused or exacerbated by vibrations at higher engine speeds under load. The fact that reducing the throttle pedal depression by a centimeter restores power suggests even the possibility that the throttle linkage is touching or otherwise affecting the ignition and/or voltage supply to the fuel pump. I would expect that if you have one or two of the 12v pigtails (originally intended for the solex) poorly secured or insulated this might result in a short and a blown fuse - but I suppose there are other possible consequences, depending upon what you might be doing with those wires.

Pictures, pictures and pictures?

Hey Percy,

Thank you for the thorough advice. It helps a ton. I'll do my best to answer everything you asked. I purchased the car like this. I've owned it since January of this year. It has an electric aeromotive fuel pump that's name I'm not sure of. I have switched fuel pumps to one I know works and it didn't solve it. The pop seemed to be a exhaust backfire. That's what I think at least. I checked and cleaned my fuel tank pickup screen but no luck. Here are some pictures of my wiring set up and fuel pump. I'll get a video posted soon too. In the video I shift to second and press full throttle until the video ends.

Thanks!

Utah02

http://youtu.be/ExlO7Jt2uFk

Edited May 22, 2015 by Utah02

[peterschop]

Sounds like a rev limiter.

[Simeon]

Back to the rev limiting rotor arm again

Does your rotor arm look like this?

[2joejoe2]

Intake manifold leak maybe? To verify not enough fuel, put some gas is a squeeze bottle rev the car, when it starts to bog squirt some fuel down the barrel.

You need to do a compression test and a leak down test. The valve train could be so worn that it can't draw enough flow to pull in a good fuel mixture.

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