Engine issue... Looking for ideas on where to go next...

[Calif240]

Hey guys... I had the car out two weeks ago and hammered on the accelerator and she laid a nice patch of rubber ... However, as soon as the rubber was done being laid, she ran weird, almost like missing a cylinder. I thought for sure I ate a plug, so changed them all out for new NGKs, but it runs the same, extremely hard to start, like it's got a bad plug. I popped the valve covers and everything looks great. I'm about to go next to the distributor and then check for a blown head gasket, but wanted to post here in case somebody had an easier idea or suggestion on what's wrong. I can get it to start here and there, but it will die on its own.

Any ideas?

Thanks,
Terry

[RECHRGD]

Easy stuff first....  Have you checked all the distributor contacts and cap for damage?

[Calif240]

Yep distributor looks fine... My O2 sensor shows its running lean 14.5-15 instead of a little under 13. Before it was mixed fine. Nothing popped or made any noise when I laid the patch of rubber... Just immediately acted like it was missing.

[RECHRGD]

PCV valve stuck?

[Calif240]

No pcv valve on the engine... I tried spraying starting fluid in carb to ensure I wasn't restricted at a carb jet, but it didn't do anything and engine just died. I also blocked the vacuum line going out to ensure I didn't bust a vac line somewhere... Nothing... 

[c00nhunterjoe]

If it has a miss, pull 1 plug wire at a time to determine  which cylinder is missing. Proceed from there.

[Calif240]

Good suggestion. I'll try that hopefully tonight and see what the results show.

In a normal "miss" scenario, the air-fuel should read more rich, correct? As unburnt fuel would be in the exhaust. O2 sensor shows I'm lean, so I was starting to head down a different path, but I think I'll start there w each plug wire since it's much easier.

Thanks,
Terry

[c00nhunterjoe]

You are thinking like its a multiport fuel injection. Its possible, but not not always. Fuel delivery could be suspect but on your scenario, but its not probable that a carb will cause a single cylinder missfire. A single lean cylinder scenario on your motor will take you down a whole different path.
   Your description of "runs weird" makes it difficult to diagnosis via keyboard. What did the old plugs look like? Did they all concur with you lean gauge reading? Any 1 plug different then the others?

[68 RT]

My car did the same thing a few years ago. Big burnout and ran bad after. Tried spraying carb cleaner etc. Finally took carb off car and and cleaned it out. After that it ran great.

[Back N Black]

Good suggestion. I'll try that hopefully tonight and see what the results show.

In a normal "miss" scenario, the air-fuel should read more rich, correct? As unburnt fuel would be in the exhaust. O2 sensor shows I'm lean, so I was starting to head down a different path, but I think I'll start there w each plug wire since it's much easier.

Thanks,
Terry

With unburnt fuel in the exhaust the 02 sensor will read lean because 02 does not read raw fuel.

[Calif240]

That's great to know! I wasn't aware that unburnt fuel would cause reading to go lean!

Thanks,
Terry

[justcruisin]

The comment that an O2 doesn't read raw fuel is correct - but that's not the whole story - an O2 sensor reads as it's name suggests - O2 (oxygen). If you have an excess of fuel in the exhaust it is generally there due to a cylinder which hasn't fired, if that is the case you will also have an excess of unburnt oxygen, as the fuel to air ratio mix is biased towards more oxygen than fuel and both are unburnt from the miss fire the O2 sensor will show a lean reading even though there is an excess of petrol in the exhaust.

[firefighter3931]

Have you done a compression test Terry ? 


Ron

[Calif240]

That was one of the "next on the list" tests. I didn't see any evidence of blown head gasket, however, so I'm hoping it's something simple. Once I get the next few tests, I'll let you know what they show. I won't be able to get to it for next few days w work and all 

Thanks,
Terry

[c00nhunterjoe]

Thats why i suggested isolate the cylinder 1st, compression test next, if all numbers are even you can move on to ignition and then fuel delivery last.

[roger dodger]

Just a newbe, but I think vacuum in fuel tank, had that on the way to Iola on second day ,my problem I think is vent tube is rusted, Like I said just a newbe Roger