well there is that possibility, i have many different things to try..process of elimination one at a time. i want to try some of the least resistance methods first..than if it comes to pulling shit off the engine to diagnose of find any other possibilities than I'll move on that when the time comes..
When looking for a vacuume leak use Berrymans Carb Cleaner But do bot spray it on any painted parts as it will take the paint off. When you spray it over a leak it will kill the motor so it makes it fairly easy to find the leak. And yes in my days of working on chevrolets I have encountered, More then once, Where the gasket did not cover the intake port. This can happen from underneath also if the heads have been shaved !!!!
Thanks Fuzzy..i really hope its something easy..chances are..its 1 of these 3 things.. vac leak near cyl...Could include carb vac leak, or PCV leak or location bad gasket fit and sucking from with in the valley or obstruction..(rag) in intake runner? i hope its one of these easy fixes.. really hate to take the manifold off, i didnt put it on, so i guess if i have to take it off, i will learn more about this particular engines history
yeah i should have went RAT..By that i ment Big Block! hey crazier shit has happened..I'll shit if i take the intake off and there is a fuel soaked rodent in the #1 runner...lol
You need to do a running compression test. See what compression is with motor running. 150 doesn't mean its good if the rest are 120psi.
I eliminated everything i could think of, so i started driving it i could feel the cylinder come and go, i swore it was ignition, next drive i took my compression gauge and plug wrench with me, pulled over on the road and ran a check on that cyl it was low, came back and pulled the head on a hunch, dropped the exhaust valve out and i could see where the seat was moving around,,, it was a lucky guess
Well ,took the front carb off ,no mouse John And nothing else I could see , rules out rag in the runner. Looking as best I can I don't see a bad head to intake fit,looks good Next is to rule out the front carb creating a vacuum leak
I blew air from the plug hole with the intake valve open ..and I can feel air coming out of the bore of the center carb. So nothing to stop fuel from getting there ,so some other reason that cyl not getting fed
Yep, PCV needs to run off the center carb. Plug the hole in the base and see if that solves it. If so, re-plumb PCV and your good to go.
For what it is worth, on my tri power I found the base gaskets for the sec. carbs did not make total contact with the base and allowed a vacuum leak. Had to use the large gasket and not the rectangular one. I have also run the set up with the sec. carbs blanked off while trouble shooting the engine issues. Sometimes easier to diagnose problems by getting back to just a basic engine.
Wouldn't it still fire with a vacuum leak? Unless it was so large it couldn't suck in any fuel? I'm not a mechanic, but I would think that a leak would lean the mixture and actually cause it to burn hotter, thus that cylinder should read higher. I know on my airplane cylinder temp goes up as I lean it out. Like I say, I'm now mechanic and am probably off base here.
I need to make some block off plates, but from what I can tell , it seems the front and rear carbs Are sealing up well , true test is run a vacuum check , and rule out any leaks . I will be blocking off the pcv to the front carb ,and working that out another day . My vacuum for my distributor is running out of the back of the center carb ,would like to leave that Alone. Tomorrow comes another heat gun test to see if plugging the port that was used for the pcv did the trick . If not ...on ward
I need to make some block off plates, but from what I can tell , it seems the front and rear carbs Are sealing up well , true test is run a vacuum check , and rule out any leaks . I will be blocking off the pcv to the front carb ,and working that out another day . My vacuum for my distributor is running out of the back of the center carb ,would like to leave that Alone. Tomorrow comes another heat gun test to see if plugging the port that was used for the pcv did the trick . If not ...on ward
I would try a leak-down test on that cylinder. Remove both rocker arms and pressure the cylinder up with a 100# of air on a dual gage tester. This will rule out the guess work and assure the rings and the valves are seating. It will make an easier job out of chasing your problem >>>>.
I just caught up with this. Vac leak...1 cyl, poor delivery to just that port under idle. I'd bet breakfast...
Well just ran a vac test ...at idle she pulls 16 steady Off idle up to about 2000rpm it pulls a steady 20 I can't tell yet if that cyl is now firing or not ..will have Heat gun back tomorrow Hell highlander ill do and pay for breakfast even if your wrong
ain't had time to read it, just went to last page from your pm...vac leak..i was a nit concerned with the way the pvc is routed when we was down there fireing it up...too much open, easy to suck in air thru those pvc's..let alone all the air that can be sucked thru the lines at the connections..i had to run clamps on my pvc on the blown 400 in my wagon...prior to that, it run slugish for a blown 400...started check and found that the blower was pulling thru the pvc so hard, i noticed it when oil started dripping from the pvc/breather... capp them puppeies and run your gun....150 temp??ya didn't have a water gauge in there last time when we fired it...bet ur ass thats water temp...no pop there... but it sure didn't have any issues when we started it inso far as rough running or idle...i;ld have to come see ....maybe tomorrow nite if ya don't get it by then...cincy bound thurs
Curious, does this vehicle have an automatic transmission? If so does it have a vacuum modulator, and if it does where does the vacuum come from, front or rear of engine. If the vacuum modulator is bad it will suck fluid into the nearest cylinder. Just a thought.
Only other possibility that comes to mind is also a little odd, but Lippy mentioned it too. Once saw a cylinder head that had been ported really big and the floor on the intake ports would not seal to the manifold. Big intake leaks into the valley and the engine would not start. Could you have one cylinder that is not sealing due to a crappy gasket or overly aggressive porting on the valley side where you can't see it?
Yeah she jumps right to life.. Just seems strange for one to be dead I pulled the carb and looked, all clear, I put it Back together ,capped the pcv , checked the spark Again,its good. Did vac check..now I just need my heat gun Back..its out on a job til tomorrow. Stop down if you got the time
I would try the vacuum gauge reading with the plug wire connected, then disconnected to verify if the cylinder is firing or not.
You don't need a heat gun... Take a simple test light and ground the clip, then slip the point between the spark plug boot and the wire. It's so easy this way...just pull it back out and in again to see if it changes the idle. Test other cyls to get the feel of it.
I don't see how a vacuum leak could only affect the #1 cylinder unless it was at the junction of the head and manifold at the gasket. I don't see why the location of the pvc vacuum would make a diffrence either. It's getting vacuum from the plenum no matter which carb it's on as long as it's below the butterflys. Mine runs colder by a heat gun reading on the header tube and if you pull the plug wire off with it running you definitely hear the miss start up so it is firing and running that cylinder. I think I would try to put the issue aside till you can drive it, as long as you feel there is no engine damage in the works. You are there I am not. I got tired of chasing ghosts and it doesn't hurt anything on my engine except logic. It has been running that way for over 2 years. And I have had 2 diffrent intakes on it. Both did the exact same thing. Plugs all read the same when you check them. Brown.
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