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Help! Dies At Low Rpm


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#16
Petros

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QUOTE (Bubba @ Aug 17 2011, 09:21 PM) <{POST_SNAPBACK}>
Yes- even with a new carb you might have the same issue if it is being caused by a bad fuel pump, clogged filters or even a clogged intake in the gas tank.

Checking the sight glass when the car is acting up would be pretty easy (5 minutes of work) compared to changing out the carb.


It is not the fuel pump, I already tried swapping that out with a good spare, I replaced the filters, and it is not the gas tank filler cap.

The car is in another state and I have to fly there to inspect it, find the problem and repair it for my daughter. So I want to go armed with as much information, and possible spare parts as possible, that might be causing the problem so I can fix it in one trip.

If it is not the pump, filters or gas cap, would changing out the carb likely fix it? Or are there other things I should check? What other spare parts should I bring?

I have an extra carb, it will only cost about $30 for a kit to rebuild it. It is actually faster to swap out the whole carb than correct the float level. This will also change all the internal diaphragms, the fuel cutoff solenoid, fix possible vacuum leaks, replace the auto choke, and a number of other parts that could be causing or contributing to the problem.

What I need to know if anyone has any idea of what else might cause this kind of behavior so I can check those too when I get back to the car.

There is several large plastic boxes, one on the firewall and one on the left fender well, that has a lot of vac lines going into them, and several electrical connectors. IF any of these are malfunctioning will it cause fuel starvation or drivablity issues? I do not think they will cause this kind of problem, but I have spares of these assemblies as well.

Thanks for any help of ideas.

#17
Bubba

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QUOTE (Petros @ Sep 6 2011, 08:54 PM) <{POST_SNAPBACK}>
It is actually faster to swap out the whole carb than correct the float level.


So, are you saying that you have checked the carb sight glass when it was acting up and you have noted that the fuel level was low?

If so, and given the fact that you have replaced all of the filters and tried a good fuel pump, the problem is likely the fuel pickup in the tank- maybe it is clogged with rust in which case you will need to drop the tank.

Double check the ignition timing and check cap rotor wires and plugs

Vac leaks- Check the rubber carb base plate for cracks (smear rtv on it if you find any) as well as the brake booster vac line where it attaches to the manifold. Check for cracked vac hoses.

#18
EuphoricBlue

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Bring a vacuum gauge, that will be the easiest way to tell if you have a vacuum leak.
Could be ignition coil fault that only shows up when the engine is warm.

#19
Petros

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fuel line pickup in the tank....it seems to me if that was the problem I would not have fuel at the fuel line and filter at the carb. That would be an easy check. But it seems unlikely since it appears to be temp related: engine cold, it starts, runs and drives normally; engine warm no fuel to the engine. That is an easy check however, blow air down the fuel supply line and see if it will run.

FYI, last time I was with the car I did not check the float level through the sight glass, but I will when I get back to austin to fix it.

Not likely timing, distributor or spark related because after it is warm, it will start and run momentarily when I spray starter fluid down the carb. I can keep it running with the starter spray but as soon as I stop spraying down the carb it dies.

#20
Bubba

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Would it run OK if you manually closed the choke butterfly rather than spraying starting fluid?

If yes- then it is likely a vac leak

If no- the carb must have been empty so it is likely a clogged fuel pickup (since you have already checked your filters and substituted a known good fuel pump).


Driving for a few miles could slosh a bunch of rust into the pickup in the tank and the suction could then make it stick to the pickup.

If the car was simply parked and idling (not moving) would it still die when it warmed up?

#21
Petros

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closing the choke makes it die, there are no vac leaks, I check for that using the starter fluid.

I am pretty sure it would die when it warmed up either driving it or when it was idling. Is there an access hatch in the back of the car under the carpet to get to the fuel sender? Some cars have a metal plate you can take off to get to the top of the tank above the sender. It allows you to check or change the sender without having to remove the tank. I do not remember if that is the case with the CRX, my Toyota and Mazda both have access plates over the tank. If there is one I can inspect the inside of the tank without having to remove it. Or do I have to remove the tank to get a look inside of it?

Usually removing a tank is a bit of a hassle, it would be worth checking the inside of the tank since this car has a history of plugging up the rear filter with crud. We bought the car cheap as a major fixer, it had not been run for a number of years but it had been garaged at least part of the time, it had been overheated, taken apart and than abandon. I replaced the engine with a rebuilt one, rebuilt the brakes and a number of other repairs, but before I ran it I drained the old fuel in the tank and put fresh fuel in it.

I do not remember the old fuel looking dirty when I drained it. I used the old fuel to run our lawn mowers and other small engines. Even so if there was ethanol or condensation in the tank it could have caused rust. It might be worth a look in the tank.

Edited by Petros, 08 September 2011 - 07:56 PM.


#22
Bubba

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Unfortunately, there is no access panel for the fuel tank, it has to be dropped...

When it gets warm and dies, if manually closing the choke doesn't help, it seems that the carb bowl would have to be empty.

Looking at the sight glass would confirm this diagnosis.

After it dies, have you ever used your hand to open and close the throttle butterfly a few times while looking down into the primary carb bore? If there is still gas in the carb, you should see a stream of gas shooting into the bore from the accelerator pump.

#23
Petros

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Yes, after it was warm and would not run, I took off the air cleaner and looked down the carb throat and could see a stream of gas (and a vapor cloud) when I advanced the throttle. IT appears there was gas in the carb, it just would not run as if it had no gas. this is why I am suspecting the fuel cut-off solenoid.

#24
Bubba

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I agree with your logic. It sounds like your tank and pickup are OK because if the accelerator pump still works then there is gas in the carb.

I have accidentally unplugged the fuel cut off solenoid before and when I did this, I was still able to start my car with a few pumps of the gas pedal. It wouldn't idle, but it was still driveable, even at highway speeds (55mph).

#25
Petros

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IT appeared to act this way at first, it would only die at idle. But as it was driven more and more it became undrivable where even holding the throttle down all the way it would run weak and die out. So it might have more than one problem. I am going to try and swap out the rear fuel filter again. IF it is full of crud than I am going to drop the tank and try and clean it out.

I do not know if it is related, but it only acted this way in the very hot Texas weather this summer, it drove all winter even if a bit balky at times (occasional stall, like it had a vacuum leak). What ever the problem it needs to be fixed.

#26
classichondaman

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It is now November. Did you resolve this? My thoughts were:

1.) if it was the fuel cut-off solenoid you should still be able to drive it by blipping the throttle

2.) if it was crud in the tank (a common problem) you shouldn't see a good stream of gas in the venturi

3.) if it had a severe vac leak it would probably not run completely smoothly when cold

....so......it still seems like a float issue.

But what happened??....

#27
Petros

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QUOTE (classichondaman @ Nov 2 2011, 09:41 AM) <{POST_SNAPBACK}>
But what happened??....


thanks for asking. I returned the first week in November and worked on it some more. I pulled the carb since I knew the choke was not acting properly and started to swap in a carb I got from the same year hatch back (I had bench tested all the components that I could and cleaned it out), and found a few differences. So I swapped those parts around, also replaced the coil and distributor cap, installed a new battery, replaced the rear fuel filter (it had a few particles in it but it was not plugged). Got it start and run finally. But when it was cold it acted like the choke was not working (bad flat spot), and it still wanted to stall below 1000 rpm. I was able to drive it once it warmed up, but it was stalling out every time I allowed the rpm to drop below 1000.

The choke was working properly, the float level was correct, and there were no vac leaks. So it appears to be something in either the emission controls or the power supply to the fuel cut off solenoid. There are a few components that will make it run too lean: the altitude compensator, and I think there is an idle air control. The fuel cut-off solenoid goes through a relay in the large plastic box on the fire wall (with all the vac lines going into it), and than into the ECM. IF there is no power at the connector than it is either the relay or the ECM. Any other guesses on what I should check?

My current plan is to grind through the service manual on all of the emission controls and see what could cause it to run too lean at low rpm, and than take one of each with me and go back after Christmas and just swap them out one at a time from most likely to least likely. This car is rather remarkable in how complex it is yet there are still a lot of these old carburated Civics and CRXs on the street.

So in summary: it starts and runs but has a bad flat spot until it warms up, and will stall out below 1000 rpms even when warm. IT is not the float level, not the fuel filter or fuel supply, not the choke, not anything to do with the ignition system, not likely anything inside the carburetor (since it acted the same with both carbs).

Anything else anyone knows about in the emission controls or things that affect the air/fuel ratio?

#28
Bubba

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If the spark timing is set correctly and the accelerator pump is working and the float level is correct in the carb, then it could be any of the components in the black boxes. I suggest that you do a devac. I did it to my 87 HF and other than a slightly high idle speed until it gets good and warm, it runs very good.

#29
civic4ever

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I keep getting confused with that screw. It is not the same as the throttle stop screw, right? And where is located.

 

It's possible you accidentally turned the idle speed adjuster down while working on it and didn't notice it. Try turning up the idle speed while it is running cold, wait for it to warm up, and see if you can bring the idle back down to normal levels when it's warm.