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Hi all
I have a 1966 mustang gt mostly original as my first car I've been driving it a lot recently and just yesterday while driving at any constant speed it misfires. But when I accelerate it's fine I have just put on new cap, rotor, wires and coil. It ran great with the new parts but now it missfires the carb is a holley 600 that needs a rebuild it "throttle pops" every now and then and sometimes "diesels" when I shut it off and runs good otherwise. The fuel filter is newer and the plugs have probably 1000 miles on them and there gaped to 35. Also there is a crane cams ignition box on it all it dose is convert from points to electronic ignition the timing is set correct aswell. So do I have a possible vacuum problem or do I need to give in and get a new carb should I just take a can of carb cleaner and spray it in or is this a symptom of a dieing fuel pump or a clogged filter I have checked all plug wires and other wires. One more thing is I put on an msd coil before and it just stopped working one day so I used the old one for awhile and when I did the tune up I put on another msd coil thinking I got a bad one the first time could this be a coil going bad. Please someone help me and recommendations or advice would be greatly appreciated ,Jason. Sorry for the long post
 

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You have a lot of stuff going on with this engine. Who installed all the electronic ignition stuff? If not done exactly right you can get problems.

Start at the beginning and verify the installation of everything. Go thru the instructions and make sure all the notes were followed. Specifically on the use or bypass of the pink resistor wire. Look at all the vacuum hoses really well. Then I would look at the carb and evaluate if it really does need that rebuild kit. Spray some cleaner if it looks really bad and is dirty.
 
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Thats an odd prob.

Check carb gas level. It should be just below the inspection window.

I would set timing to 10 deg btdc with the dist vac disconnected then test drive it.

Make sure distributor rotor returs properly to the stop.
 

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Dieseling is a common issue with retarted timing...recheck that timing.

If you state your carb needs a rebuild, then do it...surging while cruising is often a lean condition...verify your primary jet size, however ignition and timing issues need to be fixed first.
 
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excessive advance will cause dieseling especially in engines with "high" dynamic compression.
 

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lol, Did I have that backwards? I knew it was too much one way or the other...been a long while since I had one diesel on me.
 

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Thank you for the reply I checked the oil and it was 3 quarts low cryin.gif . I had recently changed the oil and there are no leaks why would it burn that much oil and how bad are the rings after driving about 500 miles. I used to check the oil evey day and it was always full so I stopped a very stupid decision. So now my plan is to change timing to 10btdc instead of 6 witch is what my Hanes manual said. Also to put in new plugs and then test drive itquestion.gif I checked everything with the electronic ignition a few times before and all is good so it seems. One more thing is fuel gets into the oil and puts it like a quart past full I'm suspecting the fuel pump but I just figured I was mention that is there anything else I should do or check besides rebuild the carb thank you for the advice. I forgot to mention I checked over the vacuum lines when I set the timeing before and they are good. I forgot another thing again the pic valve has oil in it and around it has oil on the valve cover I know it needs new rings I guess but now it really needs them. Well I might as well list my questions because this post got long.
Q1.Why is it burning so much oil with no noticeable smoke? The Rings, valves?
Q2.compresion test?
Q3. Did I destroy my engine (I think I did)
Q4. Why didn't I hear any knocking or scrapeing or low oil pressure when it got so low?
 

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Discussion Starter #8
Thank you for the reply I checked the oil and it was 3 quarts low cryin.gif . I had recently changed the oil and there are no leaks why would it burn that much oil and how bad are the rings after driving about 500 miles. I used to check the oil evey day and it was always full so I stopped a very stupid decision. So now my plan is to change timing to 10btdc instead of 6 witch is what my Hanes manual said. Also to put in new plugs and then test drive itquestion.gif I checked everything with the electronic ignition a few times before and all is good so it seems. One more thing is fuel gets into the oil and puts it like a quart past full I'm suspecting the fuel pump but I just figured I was mention that is there anything else I should do or check besides rebuild the carb thank you for the advice. I forgot to mention I checked over the vacuum lines when I set the timeing before and they are good. I forgot another thing again the pic valve has oil in it and around it has oil on the valve cover I know it needs new rings I guess but now it really needs them. Well I might as well list my questions because this post got long.
Q1.Why is it burning so much oil with no noticeable smoke? The Rings, valves?
Q2.compresion test?
Q3. Did I destroy my engine (I think I did)
Q4. Why didn't I hear any knocking or scrapeing or low oil pressure when it got so low?
 

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that much fuel in the oil? maybe your carb is overflowing.
 

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You checked the oil and it was 3 quarts low, yet you say that fuel is going into the oil pan and increasing the oil level? I'm confused. Anyway, I had a lot of fuel in my oil when I was first trying to set the timing and adjust the carb on my car as it was having a hard time starting and just dumping gas into the oil. Could this be your problem? Regardless, I would do an oil change again, with filter, and monitor it regularly. As for your other problem, I would think it would be a timing issue, especially the dieseling.
 
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it is smoking.

get in front of someone at night so they are fairly close but a safe distance then floor it for 3 seconds then look in your mirror, then let off the gas and look in your mirror. you will see smoke.

remove yor pcv and oil fil cap, shield the fill tube from fan air and rev it. you should see smoke.

you had just enough oil to keep gping, 1/2 qt less and your eng would likely be toast.
 

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Discussion Starter #12
On the dipstick when full you can see that past the full mark it gets lighter in color and smells of gas then once it runs for 10 minutes it's at full and don't smell like oil to clarify that and when it got really low there was no fuel mark on the dipstick for some reason. I had my buddy follow me home the other day and he didn't notice any smoke just that my passenger side break light stopped working for some reason it keeps blowing that bulb. But I will take off the pvc, air cleaner and fill cap and look for smoke tonight before and after I put in the plugs. I was also thinking it could be the float in the carb stuck and fuel overflows but I will keep you all posted. Thanks Jason
 

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I just got done with the compression test 1 was 170 2 was 169 3 was 170 4 was 169 5 was 170 6 was 160 7 was 169 and 8 was 171 these are surprisingly consistent and good as far as i know except 160 but that's a small difference. So I put in new auto light 45 spark plugs gapped to 35 and fired it up and the miss fire is still there damn. So now I'm going to put on my old coil in place of the msd that's in it now. Because my last msd coil died in 10 miles but it's for stock and high energy ignition systems so.. no idea why it would give up but it's happened before. Do hopefully that it also to change the timing. If you can tell me anything about my compression test please do and also anything about the miss fire I'm always looking to Lear and of course get my car fixed but I know I have provided limited information. Thanks Jason

For the compression test I rented one at auto zone and removed all spark plugs then went from each cylinder. I used a pair of pliers to jump the solenoid and watched the gage until it stopped going up and bounced and I took the higher number.
 

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I would try old distributor wires if you still have them... Sometimes new stuff that does not work out of the box. Check if missfire is gone.
Alex
 
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ok your compression test should have been done with the coil wire removed and the throttle propped atr least 1/2 way open.

if those results are accurate it suggests your rings are good and the oil os leaking from your valves, howver, this is too much to leaak past your valves. the gauge could be up to around 20 psi off if it is a cheap one.

are you positive there is no massive oil leak?
 

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fuel in the oil, anyone think of a bad fuel pump? this would cause a lean fuel mixture also. bet the innerds of the engine are real clean now. this would also reduce the viscosity of the that will allow the engine to burn the oil fuel mix without smoking, also cause dieseling as the fuel in the oil provides fuel to run on.
 

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With that much gas in the oil why did you not change the fuel pump already? You mentioned that 3 days ago. You seem to know the basics, we all need help with the fringe things.
 
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