Will not start (sort-of randomly)

Hi all,

I have had this sort-of intermittent starting issue with my caprice ('85 4BBL carb. V8 305; 110,000 miles) for about a week or two.

Sorry for the long post. I have an issue with giving too much information sometimes :tongue: I have put some important stuff in bold for your convenience.

The engine will crank very well but not start after it has reached operating temp. and then left to sit for 20mins to an hour or so. However, if it sits for 4 or more hours then I can start it again without any issues (don't even have to pump the gas). Usually under 20mins of it being off I can restart it too.

I'm very confused as to why it will restart after 20mins or less of being off, then NOT start for a time period of 20+mins to an hour maybe two; then finally be okay to start after a few hours or more of being off...

The above seems to usually be the case, but sometimes it will start when I want but it can be VERY difficult.

It runs good (like normal) when it is running. Upon a successful restart (without it sitting for 4+ hours) the engine wants to die and has very low rpms -- perhaps not more than 300 it sounds like unless I help it.


Here's what I've done so far:

Diagnosed EFE (Early Fuel Evaporation / Heat Riser) valve -- is actuated whether engine is cold or hot, determined that the TVS (Thermal Vacuum Switch) needs replacement. Currently I disconnect the hose and plug it back in once the engine is warm. (Does not actuate again once re-inserted). AFAIK this will not cause the starting issue.

Checked charging/starter circuits for loose connections and misc. issues. Turned out to be in good condition. Motor and Solenoid switch terminal on starter were sort of snug but not very tight; cleaned up and added star lock washers for better conductivity; should be good now. I doubt there are poor connections elsewhere but even if so does not explain why starts extremely easily upon 4+ hour rest (car off).

Got a new battery (free replacement) and voltage is good (12.6v or better at rest) and provides plenty of power when starting. While cranking but not successfully starting, everything still sounds the same -- I can tell there is a lot of power (normal) while cranking. The engine just doesn't seem to want to start.

Replaced air filter with a new one. (Normal maintenance)

Discovered that 0.3 A (300mA) of power is taken from battery whenever alternator charging wire is connected. The alternator is nearly new (re-manufactured). I disconnect the negative term. on the battery to avoid it being drained. It can survive 24 hours or so while still being connected and be able to crank just fine. When the alternator is disconnected I get a reading of zero Amps (my multimeter is not very sensitive).

Checked fluids: All seem nominal.

Made sure belts were not too tight nor too loose.

Checked carb. fuel delivery -- Accelerator pump works great and fuel is being pumped in when pedal is pressed down.

Checked for flooding -- It does not seem to be flooding (I looked through the primary throttle plate and there was not even a small pool of fuel in there from what I can see).(Also, I usually don't pump the gas unless it won't start after trying for a few seconds. Then I gently pump maybe once; so I progressively add some more gas if it won't start. AFAIK I'm not flooding it).


Thoughts:

I did not check the fuel delivery pressure because the car runs good (normal) when I am able to start it. At WOT there is plenty of fuel.

Cap and rotor need replacement? Could this cause intermittent problems?

Engine is just getting too old? I've heard that excessive oil leaking into the combustion chambers can make starting difficult (makes sense). However, if this is the case, how come it will usually start if restarted under 20mins since last run and/or a 3+ hour rest? But not the time period between 20+mins and a couple hours. I do loose some oil over time; I seem to have lost about a pint or so over about 2 months, which is probably about 750 miles.

Could heat and/or time somehow be affecting something I'm not thinking of? Hence the reason for the odd times when it will or will not start. For example, under 20 mins the engine is still hot. During the time period from 20+mins to a couple hours, the engine is warm or cooling down and more time has elapsed (for oil to trickle down, etc). After several hours or more engine is cool, fluids such as oil have completely trickled down, etc.


Thanks for your help. This is starting to drive me crazy...

I have been having a similar problem with my caprice. For me, I only have this issue when i drive the car a mile down the street to the coffee shop and shut it off. Of course at this point the car is barely warmed up at about 110 degrees. Once i get back and start the car it barely idles and doesnt respond to feathering the throttle. Only way to get the RPMs up is to floor (which i'm told is what you do if its flooded) until it starts running smooth and clears out the leftover gas. Another thing, on hot days sometimes my car has trouble starting so it might indicate a choke problem?

So basically my guess is your carb is flooding, or its a choke issue, or maybe theres some kind of an air leak (possibly the gasket between the carb and the intake manifold). Another thing, on hot days sometimes my car has trouble starting so it might indicate a choke problem?

Next time it doesnt start try holding the gas to the floor while you crank it over and see if that gets it running...of course don't let the RPMs fly up once it gets going. That stuff is in the car manual if you still have that.

replace ignition module ...

buy a new not rebuilt alternator..diode is blown on yours, bleeding down the battery ..

replace ignition module ...

buy a new not rebuilt alternator..diode is blown on yours, bleeding down the battery ..

I agree with the above.
I was thinking carb but since you said it starts after a while, that eliminated that thought..

.3 amps is to much draw on the battery.

Thanks guys. I do try putting the pedal all the way down to clear possible flooding (after trying to start normally with a half-pump of the pedal, then a full pump or so). But that doesn't make a difference unfortunately... Perhaps it could be a choke problem; I'm not sure. Could it be getting too much air? The choke actually opens on its own a bit because it gets so extremely hot here that the ambient heat starts to make the choke start opening...

I will try replacing the ignition module. The alternator can be replaced in the future when I have $$ but I always disconnect the battery so there is no drain on it overnight.

Do I need a new cap and rotor? I still don't understand why it works and doesn't work in the way I described...

Thanks guys. I do try putting the pedal all the way down to clear possible flooding (after trying to start normally with a half-pump of the pedal, then a full pump or so). But that doesn't make a difference unfortunately... Perhaps it could be a choke problem; I'm not sure. Could it be getting too much air? The choke actually opens on its own a bit because it gets so extremely hot here that the ambient heat starts to make the choke start opening...

I will try replacing the ignition module. The alternator can be replaced in the future when I have $$ but I always disconnect the battery so there is no drain on it overnight.

Do I need a new cap and rotor? I still don't understand why it works and doesn't work in the way I described...

you have an electric choke stove/spring. these when aging as most springs when aging loose the tension...so therefore you when engine cold take air cleaner cover off give gas pedal a hit to the floor boards and check the the choke plate is fully closed..If not see if its dirty/sticking if not get a new choke assy....the chevy q jet choke stoves fail often. the olds 307 engine also used in this age group use exhaust flow to heat up the choke this is more reliable ...

ignition modules are sensitive to arcing and excessive heat ..usually they slowly fail with very random missfires ..then hard starting ..very intermittent..

I took off and inspected the ignition module. It was not very tight and there was very little silicone grease (the dielectric stuff I believe).

I simply took it off, cleaned it, added new grease, and bolted it back down snug-tight.

It works much better now and starts almost instantly every time.

Thanks for the help! :)

I took off and inspected the ignition module. It was not very tight and there was very little silicone grease (the dielectric stuff I believe).

I simply took it off, cleaned it, added new grease, and bolted it back down snug-tight.

It works much better now and starts almost instantly every time.

Thanks for the help! :)

the grease to use is the heat sink compound/not dielectric grease...go to radio shack to get this HEAT SINK COMPOUND...

GOOD FIND / the loose hardware would cause the module to overheat ...