Engine running rough and at wits end!

[pwdcougar]

Was driving my convertible last week on a long trip. 4 hours total. On my way home it started running rough. I figured I was low on gas and that was the problem so I filled up with premium gas.

It is still running rough. It runs rough at idle and you can feel it at higher RPM too.

What it does:
rough idle
low vacuum 10-12 at 1200 rpm
vacuum gauge fluctuates
wildly different exhaust manifold temperatures. Front and back on bank one are above 400. The inners are 250.

I've tried everything I can think of.

new plugs
new wires
removed and cleaned the original carb
rebuilt another carb of the same type
checked for vacuum leaks
1) removed and plugged all vacuum lines
2) sprayed around the intake and carb with starter fluid
3) replaced the carb gasket 3 times
Checked compression but I've only done 3 cylinders 120 - 130 psi
Changed the timing and checked vacuum advance
Monitored the valve train with the valve covers off while cranking. All rockers move as they should.

Please can someone help?

Thanks

Paul

[TJ's Chevy]

Have you sprayed carb cleaner around the intake ports to see if you have a vacuum leak there?

[pwdcougar]

Originally Posted by TJ's Chevy

Have you sprayed carb cleaner around the intake ports to see if you have a vacuum leak there?

Yep. I've sprayed carb cleaner and starting fluid over the entire intake area.

Paul

[TJ's Chevy]

What's your valve adjustment?

[pwdcougar]

Originally Posted by TJ's Chevy

What's your valve adjustment?

When I had the valve covers off I went though the valve adjustment procedure outlined in the shop manual. All the torque specs were close if not spot on.

Internet searching has me now thinking about a blown head gasket as one of the symptoms is a rough idle. There is no coolant in the oil or oil in the coolant though.

Tomorrow I'll do a full compression test and post the results.

Thanks TJ for the ideas. Keep them coming. I'm praying that someone will hit what I've missed.

Paul

[TJ's Chevy]

I'm gonna back track a little bit. lol What engine is it? How many miles on it? Rough running can be one or many problems. So we'll go through one step at a time.

[pwdcougar]

Originally Posted by TJ's Chevy

I'm gonna back track a little bit. lol What engine is it? How many miles on it? Rough running can be one or many problems. So we'll go through one step at a time.

I was afraid someone was going to ask what motor. It is a 351w in my Cougar. The motor has 80k showing on the odometer so it could be 180 or maybe 280? It has an RV cam of unknown specs and an Edelbrock performer intake and 600 cfm carb.

I'd ask the Cougar forum I belong but they can't even come close to comparing to the knowledge and depth that is found here.

Paul

[cadillac_al]

At least you checked the vacuum and started heading in the right direction. It sounds like you did everything to find a vacuum leak. The next step would be a full compression check. I wonder if fords can still run if the timing chain jumps a tooth? Could the exhaust be plugged? (potato in the tailpipe lol).

[68gmsee]

Just as an fyi, a compression check may or may not find a head gasket leak or even a cracked head. Sometimes these problems won't show up until the engine is fully hot.

Also, depending on the location and how bad it is, you may not notice a noticeable difference in coolant level. The best thing to do is to have the coolant tested for exhaust contamination and/or do a leak down compression check on the engine.

Check spark plugs to see if you notice a difference in one of them. I usually remove them all at one time making sure I keep track of which cylinder they go to.

[TJ's Chevy]

I was thinking it was a straight 6. haha 120-130 pounds sounds low for a V8. I don't know what the compression spec are for a 351W. Didn't these engine have a "variable timing" deal of some sort?

[pwdcougar]

My issue with my initial compression test was that the starter sh*t the bed. New starter today and I've done a compression test with all the plugs out.

Right side of the engine (1-4 for Ford) 150, 145, 155, 145.
Left side of the engine 155, 135, 140, 150

I'm running a Pertronix unit in the distributor. I'll swap in points and my spare Pertronix.

The spark plugs all look great but they only have an hour of running on them at the most.

Thanks guys and keep the ideas coming. I'm ready to borrow a backhoe and bury the car at this point I'm so frustrated.

Paul

[pwdcougar]

Using my home made piston stop, I've verified that when the engine is at TDC on cylinder #1 the rotor is pointing at #1 on the cap and the timing marks on the balancer are aligned. I'm off to the parts store and I'm going to pick up new intake gaskets and a thicker carburetor gasket.

This has to be an intake leak and I'll find it even if it kills me.

Paul

[TJ's Chevy]

Well if you sprayed carb cleaner around the intake and there was no change in RPM then I don't think its intake....What IS your initial set at? Sometimes factory specs can be off.

[Hollow65]

That 135 on the compression check is a tad low. Below the 10% mark

[pwdcougar]

TJ this engine has always run best with a lot of initial advance. I've run it as high as 20 before. Right now it won't run right at any timing setting.

The car was running great and started to run rough after 3 hours of driving. What could have happened at that point? A friend keeps telling me it is bad gas however it ran rough before and after filling the tank at a station that does an insane volume of sales.

When I first started tinkering with it, I tried cleaning the original carb by pouring small amounts of fuel rail cleaner down the throat of the carb without letting it stall. At times it would start to run better.

Paul

[pwdcougar]

Originally Posted by Hollow65

That 135 on the compression check is a tad low. Below the 10% mark

Is it possible that that one cylinder is making it run this bad?

Paul

[pwdcougar]

Today the carb got pulled off and I decided to check the intake torque. Many of the bolts were at best finger tight. I'm hoping this is my problem. Of course Sunday afternoon no one has the good FelPro gaskets in stock.

Paul

[68gmsee]

Originally Posted by pwdcougar

.....

When I first started tinkering with it, I tried cleaning the original carb by pouring small amounts of fuel rail cleaner down the throat of the carb without letting it stall. At times it would start to run better.

Paul

pwd, pouring carb cleaner down the throat of the carb will do nothing for the inside of the carb. You'll have to take it apart to do a complete cleaning.

[pwdcougar]

Originally Posted by 68gmsee

pwd, pouring carb cleaner down the throat of the carb will do nothing for the inside of the carb. You'll have to take it apart to do a complete cleaning.

Yep. At the time I thought I might have a stuck lifter or valve.

Paul

[HumphreyMurdoch]

I'm no engine diagnostic expert. But with the vacuum gauge bouncing, makes me think broken intake valve spring? Just a thought

[pwdcougar]

Humprey would a bad valve spring show up during a compression test?

Keep the ideas and thoughts coming guys and thanks for all the input.


Paul

[TJ's Chevy]

I wonder if it detonated on you. Too much advanced timing and not enough octane will cause detonation.....by any chance did you hear pinging or knocking under acceleration at all?

[pwdcougar]

Originally Posted by TJ's Chevy

I wonder if it detonated on you. Too much advanced timing and not enough octane will cause detonation.....by any chance did you hear pinging or knocking under acceleration at all?

TJ no pinging at all and the acceleration was as good as ever. I'm really hoping that new intake gaskets will do the trick. They won't be in till late Tuesday.

Paul

[HumphreyMurdoch]

I wouldn't think it would affect compression much, valve is still opening the same. Just weaker to close while running. I haven't dealt with that issue, personally and not sure how to accurately rule that out or not other than visually inspecting the springs. Wish I could be more help.

[HumphreyMurdoch]

http://www.aa1car.com/library/valve_..._diagnosis.htm

Here's some reading on weak valve springs, also brings up intake & head gasket leaks.