Jump to content
HybridZ
Onion

Cranks but doesn't start

Recommended Posts

I've been messing with it for about an hour now and can't figure out why I can't get my 73 240z to start. 

I drove last night and it ran great. 

 

When I crank it I can hear it almost turn over, but I've tried plenty of times and it's not starting. I am getting fuel to the carb (single holley 390). The fuel pressure gauge before the carb shows 4 PSI, which is what it's always been running at. When I give it some gas, I can see and hear it spray fuel normally. I've tried starting fluid and I'm getting the same results. I thought it would be a spark issue, so I took a multimeter to the coil and it's getting power with the key in the "on" position. I then took out a plug and set it on the valve cover and cranked the car and I am seeing a spark. What could be the issue here? The only other thing I can think of is that something might have gotten wet. I left the car out in the rain all morning and it was a little wet under the hood, but not unreasonably so. 

 

The coil is a 3 ohm flamethrower coil and it's got the Pertronix ignitor electronics rather than a points distributor. 

 

Edit: My plugs are pretty dirty because the car burns oil. I've done loads of reading about it and it seems that the general consensus on the matter is to ignore it as it isn't worth the money to "fix" the issue and just keep topping it off every now and then. The spark on the plug closest to the driver (number 1 I believe) was orange. Should I test all the others while I'm at it and see if it could be an issue related to a weak spark? I've never had any problems cranking over, if it's a weak spark, shouldn't the car gradually get harder to start, instead of going from an instant start to no start? Also, the coil only reads 10 volts with the key in the "on" position, could it be too weak to produce a good spark during compression and cause it to not start?

Edited by Onion

Share this post


Link to post
Share on other sites

I had an ignition module go bad to where it produced a weak orange spark that wouldn't start the engine without starting fluid.  Once it started it seemed fine (although I didn't drive it), but it would not even pop without the fluid. Worth a shot,maybe.   Mine was a GM HEI module, not Pertronix.  Installed a new module and I was back to normal.

Share this post


Link to post
Share on other sites

I was going to ask about the colour of the spark, but you mentioned it in your edit.

 

You have a weak spark and this is causing your issue. The spark should be bright blue or white, orange is weak. Add the pressure in the cylinder and there may not actually be any spark at all. You could try closing up the gap real tight to see if if will light off, but you likely still won't be able to actually drive the car, if it does light off.

 

The 10V at the coil is low, but not unreasonably so, though I would assume this is a measurement without the engine running, and while cranking the voltage could drop to level too low to actually light the engine, if everything else was good.

 

Do you have a battery charger/booster connected? 

 

If the battery has a higher voltage, you could use a jumper directly to the coil/ignition system to provide this higher voltage to see if that's the root cause of your issue. With the length of wire between the battery and the coil it's very possible that the voltage drop is too much, especially if the battery is weak.

 

Also disconnect the ignition wire from the coil, and measure the voltage with the circuit open, if the voltage goes up significantly then there may be a problem with the coil or the ignitor system you are using if it also feeds that.

 

So in closing you have a weak spark issue and you need to track down why. Could be voltage supply or actual component failure.

Share this post


Link to post
Share on other sites

I'm not getting any spark. It could be from having cranked it so much before because it's not cranking as hard as it was earlier. Also, I tried taking the coil to distributor wire and unplugging it at the distributor side and laying it on top of the valve cover and cranking it (as suggested on zcar to other people, found it in a search) and I wasn't getting anything. I then pulled the number 3 plug and tried again to see if I was still getting spark, and there was nothing. Spark is gone. 

 

The 10V measurement at the coil was after having cranked it a few times for about 5-10 seconds each crank, so it could just be that the battery is getting low. 

 

I don't even own a battery charger/booster, but I could try it with a friend's car jumping mine.

 

I'll go check and see what the voltage reads with the circuit closed (to establish a new baseline, I doubt I'm still getting 10V), and open, and I'll report back. 

 

Thank you for your help, six. 

Share this post


Link to post
Share on other sites

Check voltage on the battery itself. It should be 12.7 volts with no load. If you have less than 12 volts your battery is not good. Check the fluid level in the battery and ensure it is at proper levels and then get it on a charger to see if it will come up to over 12.5 volts. If it stays below 12 volts you better plan on getting another battery.

Share this post


Link to post
Share on other sites

Tested the battery and I got 12.6. Tried to fire it up, it started instantly this morning. Took it for a spin to recharge the battery, all went well. Parked it, tried to start it again, no issues. Thanks for the help. Something must have gotten wet or moist from the rain and prevented it from starting. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×