# Pontiac 400 CU IN driveability issue



## LastOutlaw (Jun 30, 2009)

My son has a recently built (15,000 miles) 400 Pontiac engine in his 72 Catalina 2 door. It has new points distributor in it. It has a mild street cam in it and has been running great for him for a year or so. Recently while sitting at a light it began to run very ragged and seemed to be missing. He replaced points, condenser, plug wires, plugs, distributor, checked spark on all cylinders, visually checked all lifters, pushrods, rockers for actuation, compression is between 140 to 160 on all cylinders, visual check on valve springs, manually checked compression on number one cylinder timing with spark on that spark plug, swapped carb with the Holley on my GTO. Nothing seems to cure it. We are getting ready to drop in an 80s era HEI distributor as our next step to try in eliminating possible problems. Also on another note. His timing mark does not show when shooting with a timing light and never has even when running right. Is it possible that his cam was installed 180 degrees off as well as his distributor 180 degrees off and run right?
Any ideas?


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## pontiac (Mar 6, 2011)

put timing light pickup on each spark plug wire while engine is running. The light on each should be uniformly flashing. if not, look at those cylinders with problems. all bad, then change cap and rotor and look at point wire from coil to dist as well as coil wire. what happens if vacuum advance is connected \ then plugged, if timing mark has never been correct, where is it showing? it has to be somewhere. if cam is 180 off, then no. 6 cylinder is no. 1, so put pickup on #6 and do marks line up? So then you know, otherwise you can move the pickup to each cylinder to figure out if one of those is acting as #1, then you could move the wires on the cap or reinstall the dist. so dist. no. 1 matches. But that would be crazy, better to just start all over with TDC and dist. location for engine #1 location. also when running spray carb cleaner around carb and carb case gasket, could be vacuum leak at base gasket and the change to another carb did not seal the leak. disconnect \ plug all vacuum hoses on carb, incl. power brake booster and PCV. how does it run now? vacuum gauge on engine will tell you a lot.


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## LastOutlaw (Jun 30, 2009)

*yes*

Yes, and thanks, the timing mark issue we can work around or live with. The driveability we can not. I did spray carb cleaner around the intake and didn't find any leaks. We have fire on all cylinders as well both when shooting with a timing light and checking with the plugs out.


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## Thumpin455 (Feb 17, 2010)

The cam turns once for every two turns of the crank, so the timing mark comes around on #6 and on #1. If you have the wires on it 180 off, then it wont run.

The stock balancers have a plastic elastomer holding the outer ring to the inner hub. These can slip over time and the mark wont show up when #1 fires. Its a relatively common thing, and I check the stock balancers I use when I assemble the engine to ensure it hasnt slipped. Put #1 at TDC (top dead center) with both valves closed and note where the mark is. If it isnt where the pointer on the front cover is, then it has slipped and needs replaced.

Check for a bent pushrod, you can do that by pulling a valve cover and watching the rocker arms as you spin the engine with the starter and the coil disconnected. If you suspect one is bent, you can hold two of them together while rolling them in your fingers. If one is bent you will see it easily. If he has had any high RPM fun, it is a definite possibility. Depending on which heads it has, you could have a screw in stud worked loose, or a pressed in stud pulling out. Like it has already been said, it could be a vacuum leak, or it could be a burned/bent valve.

For reference #1 is drivers side front cylinder, its important because Fords have it on the passenger side.


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## LastOutlaw (Jun 30, 2009)

*Update*

Update for everyone who has been offering possible solutions for this thread.

We ordered an HEI distributor and installed it. Vehicle runs somewhat better now but seems to have a lean misfire type of situation. Engine seems to idle more smoothly but is lopey which may or may not be due to the streetable cam. When in gear the engine seems to be missing and will drive but runs pretty crappy. If the secondaries are opened while driving carburetor backfires badly. He said when he started it today and there was one very loud backfire out of the tailpipe. Someone told me this may be a fuel pump failing but I'm a bit hesitant to believe this is thew case. We are getting ready to run a leakdown test on all cylinders and I would think this would tell us if we have a leaking or burnt valve. ( I sure hope not) We did pull the valve covers and inspected for rockers moving as they should to make sure we hadn't bent a pushrod or something along those lines and everything looked right. It looked like all valves were opening and closing as they should. All valve springs looked ok during visual inspection. Again, no vacuum leaks evident when spray checking with carb cleaner


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## geeteeohguy (Feb 2, 2008)

Did you eliminate the power brake booster hose like pontiac said? To me, it sounds like it's running too lean. Try drizzling a little carb cleaner down the carb when the engine is running at idle. If it smooths out/speeds up, you're too lean and have a vacuum leak. If your vacuum gauge holds steady vacuum, you do not have a valve problem. You can disable the ignition and crank the engine to determine this. A weak cylinder will give you uneven cranking....you'll hear it when the engine is turning over as it speeds up when the "dead" cylinder is up on TDC. Check the basics first.


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