97 Ram 1500. Codes 21 & 43 o2 sensor and primary coil. I hooked up a timing light and it appears that the lugs are firing. I know there is gas present. Will the o2 prevent starting and why are the plugs firing if the primary coil is in the codes?

TIA

 

welcome to df...

well besides the codes, have you checked the basics yet? cap rotor & plugs in good shape? any one of those will cause ignition problems. are you getting spark at all off the coil?

 

You need to check your fuel pressure also, weak fuel pressure can cause the engine not to start. I have got the primary coil code ever since I installed my MSD box on my ram. It wont set a CEL but it is always there when I scan it.

 

to expand on silvers comment... should be 49psi +/- 5psi IIRC. there is a link at the top of the forum in the info thread which takes you to the merry christmas thread which will lead you to a FSM download link. it's for a 2001 but that will tell alot of info that will apply to your truck. fuel pressure included.

 

Thanks for the fast replies. Excellent info. I dl'd the link from the christmas thread, thanks for that.
I am leaning toward fuel pressure now. I will check that next and let you know the result.

 

I removed the cap from the fuel rail and pressed the thing in the center and no fuel came out. I assume this means there is no pressure. Is there a reliable check for the fuel pump relay other than replacing it?

 

If you look at the relay, there is a wiring schematic on it. just jump the plugs-also check the auto shutdown relay.

 

I finally found the test procedure in the manual I dl'd from the christmas thread.
This is a fantastic forum. I am hoping for a bad relay, but my experience is the most expensive unit is usually the culprit.
The sending unit was bad when I bought the truck, so probably time for the pump.

 

Find the relay under the hood and then put your hand on it. Have some one turn the key on and feel for a click. If the relay doesn't click then you know it is not working correctly. I work on cars everyday and I use this method so it should work just fine for you.

Heres another thought also. I think all the relays are the same under the hood, so you could swap the relay with another one and see if that takes care of the problem. Just make sure the relay you swap isn't something that is real important.

 

if it is the pump, there is a DIY writeup for a fuel pump swap in the DIY forum, have a look, it may help some.