I've got a 1990 mustang that I just put together. Had all kinds of problems got almost all of them sorted out. When I try to start the car it will just turn over unless I pump the gas then it will start but will not run unless I hold the gas. It's killing plugs fast so I took the number 5 plug out to check for spark while I was turning it over and it didn't have spark so I held it to the header and it started sparking and the car fired up and ran as long as I held the plug to the header. So I thought it was gonna be a ground issue. I checked all my grounds and even added one. I have one from the passenger side lower block the the chassis,one from the bell house to the firewall,from the starter bolt to the chassis and from a water pump bolt to the chassis(had it from the head to the chassis but no change when moved). Not saying it's not a ground issue but I have checked them all with no luck. Any help would be greatly appreciated.

 

Sounds like more of a fuel problem.

 

I've got 39.5 pounds of fuel pressure. It starts without pumping the gas if I hold the plug to metal like the header

 

Try a ground directly to the head

 

What do you mean direct to the head? I had one to the head and it didn't seem to make a difference.

 

You should have a ground directly from the battery to the engine. So you are running the engine with the #5 plug out and touching the header? Dear god please don't do this anymore. You are going to start a fire.

If I am totally misreading this please start over again from the beginning.

 

I was just seeing if I was getting spark and it fired right up if I touched the plug to the header not just setting and running it that way. Battery is relocated to the back and theres not a ground running from there to the front it was this way when I got the car. I will try that next. What size ground?

 

Dumb question... you added all the grounds to the chassis, how is the condition of the ground cable from the battery to the chassis? If that contact is corroded adding more grounds elsewhere won't help. Also what size cable is it and how long?

Edit: also, the spark plug won't have a ground when its unbolted, so it makes sense that you didn't get spark holding it in air. The fact that it sparked when you touched the header means that the header is grounded. So idk if ground is your issue but id still check the battery cable.

Assuming its efi? Stock, modded? MAF in decent shape, idle valve , throttle plate gummed up, idle air port in throttle body, etc can cause bad idle

 

Yes it's efi and maf is almost new