The problem seems to be related to the engine compartment temperature. It can reach 5,000 RPM's just fine from cold start, can drive for around 5-8 minutes from cold start with no problems. Once engine is warmed up, it is losing combustion and regaining within 3 seconds at random. Idles just fine, problem is with maintaining speeds in gear and maintaining higher RPM's in neutral. Loses combustion at High rpms, anywhere from 2 thousand to 5 thousand and will fall below 500 rpms, then build back up to idle. It doesn't die completely.

Mechanical Fuel pump was replaced at the beginning of May. It has the correct 'S' shaped hose running into the fuel pump. I thought it might have been a clogged fuel filter, so that was removed. I cleaned and rebuilt the carb and it seemed to improve, but it is still giving me the same problems once the engine warms up.


Could I be losing fuel pressure while in gear?
Can a clogged sock in the gas tank cause this? It'd be the same as a clogged fuel filter, right? I wouldn't think this would be the main cause, because when the engine is cold, it doesn't act up at all.
Why is this only happening after the engine is warmed up?
I got the car up to 90 and 4 minutes later, I am holding my breath trying to maintain 40 mph. This has me baffled, it is a new problem that has just sprung itself on me, right as I was getting the car inspected.

 

has your choke gone out of adjustment? if you have electronic ignition, heat could be causing a part to fail intermittently.
jeff

 

A catalytic converter can do that when it heats up if it's failing. IDK if your car has one though.

 

I'll wire the choke open and see if anything different happens. I don't think it will, but I'll give it a shot anyways. It has points. Dwell is set at 30.

PO put catalytic converters on it. How can I check to see if they are still good or if they are clogged up? If it's failing it will start glowing red from the heat right?

Thanks guys.

 

Being it is a "new" problem, clearly something changed. I would say "yes" to your inquiry regarding the sock in the tank. Run for awhile and the suction pulls all the crap in the tank to the sock restricting flow. Shut it down and the crap falls back to the bottom of the tank. Possible. I doubt that is the problem though. What kind of carb are you running? Rochester? If so, how about the filter element in the carb fuel inlet? Just throwin stuff out there.

 

It's the stock q-jet , Rochester. I pulled the little filter out of the carb itself when I took out my in-line filter. The thing is, it will idle and run (low or high speeds) until the engine gets warmed up.

 

Had a bad coil cause that same problem.

 

I'll change the coil and see what it does.

At this point I think it's an electrical problem. Last night I fired it up from a cold start, I let it idle for a little over 40 minutes, no problems at all, the spal fans came on and off at least twice. So I don't know if heat is really what is causing/ triggering my problem. While in park I got the rpm's up to 5 thousand and it didn't have any problems at all. Took it out on the road, I'd say my average speed for the whole trip was between 50-65. It started cutting out on me, I let up off the gas and went a little further then it just died on me, completely. So at 9:30 at night on the side of the state highway, I'm taking the carb apart to take a look see. The entire bowl was filled with gas, the float was working properly, the accelerator pump on top of the carb was working just fine.

I let it sit for a few minutes, then put it back together and it fired right up and didn't give me any more problems.

 

That sounds like something electrical. Did you replace the coil?

 

Not yet, I thought I had an old coil that I could just swap, but I don't, so I'll have to go into town to get one.

I took another look at the carb, the accelerator pump is slow to rise after being pushed down. I think it might be catching on something inside, but if they accelerator pump was pushed down, wouldn't that be the same as holding the pedal down. It should be going faster or maintaining speed instead of slowing down.

Could it be hanging up and being pushed all the way down and flooding the carb while I'm going down the road? It'll cut out, I'll let up off the gas and it will come back to life.

It's not the choke and the cats aren't glowing red. The fuel sock has a couple of pin ***** holes in it and looks like something sharp was dragged across it, but not cut completely. There is some trash/junk in the bottom of the tank, but it doesn't look like it's getting sucked to the fuel sock.

Thanks for the help guys.

 

Also check that your fuel tank is venting properly.

 

I had a distributor act up like that If the car jerks rapidly under acceleration. like someone is turning your key on and off.

 

Here is my list of things to check:

Points ignition
1. COndenser loose on breaker palte
2. Breaker plate ground wire broken or shorting when avacuum advance moves
3. Primary wire- from coil to points is bad
4. The resistance wire form the ignition switch to the coil is bad.

HEI
1. Rotor is going bad
2. Module is overheating- no heat sink grease on the bottom
3. Pickup coil wire broken and seperating when vacuum advance moves
4. Coil is leaking and jumping to ground.

A fuel/choke/carb problem cannot be there one second and gone the next. It'll run out of gas and die, then you have to crank a long time to refill the carb. If the choke is too closed it's going to blow black smoke and load up. If the choke is too far open(?) it'll be hard to start when it's cold.

 

Exactly like that. I'll let up off the gas and it'll either recover or it will die. It'll recover 2 or 3 times before it completely dies on me.


Thanks for the list Tim, I've got points on the car, I'll give all those spots a look.

 

What an awesome list, my thanks to you Tim too.

I have a 74 BB with the same type of problem as well, carb was rebuilt last summer and it's run fine until yesterday.

I'll check all that. Thanks again.

 

Here's the problem, your points, cap and rotor will be fine because it's the shaft and bushings that have play in them. This lets the car idle but when you rev it under load, the shaft moves .010 and messes up the dwell. So the only fix is a rebuild or replacement. If your not big on matching #s. Just go to Napa. Thay have complete distibutors with points cap and rotor for cheap! I paid $47.00 for an Oldsmobile 350 Dis.

 

Take a flashlight and look in the gas tank. I'll bet you see a lot of crud in there.

 

I've replaced the coil, took a second look at some wires that have given me problems before. Those were alright, started looking at everything on your list, that I could see and get to from the top of the engine and nothing appears out of place. The resistance wire is the black one and the orange wire is the hot wire going to the coil, correct? Tim, do you know the proper number of volts that should be flowing through that resistance wire?

I think this could be a possibility. I pulled the rotor out of the distributor and the first thing I saw, was the the points and the lack of a gap. I didn't adjust it, put everything back together and it fired right up.

I'll dig further into the wiring this weekend and see if I can find out where my problem is at. Thanks for all the help guys.

 

The wiring was a mess, that's the simplest way for me to describe it.

After getting the wiring fixed properly and my starter wired back up, it seemed really sluggish in turning the engine over. I have been disconnecting my battery cables from the battery, because I thought I had a drain. As it turns out, I believe my car has been running off of my battery, instead of my alternator. I started the car up and then disconnected the battery and it died. I'm going to take my alternator into town tomorrow and get it tested to see if the alternator is bad.

I'm not losing my mind here, the car is started off of the battery and the car runs off of the alternator, correct?

 

It should be able to run with the alternator only.