The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by Retro Jim, Sep 11, 2011.
Have you performed a vacuum test?
Had a 302 that acted like that one time and it turned out to be the plate in the distributor was moving around-changed the distributor and the problem went away.
Check what Cam is in the engine ,if it was rebuilt as you said ,possibly the cam mfg. uses the 351 Windsor firing order? some mfg. of Cams do this even if the cam is specified for a 302,found this out the hard way.Gerry
I am going to look into that later today .
Go away gfigu44, you scammer!!
Jim, I'm guessing you do have a major intake leak on the driver's side. The symptoms you're stating sound familiar...like that of any engine that has a vacuum leak, especially at the base of the carb...runs good when you give it the throttle, ('cause you're compensating for the lean condition) but once the engine comes up to speed, and runs out of the extra gas, or you let it idle, it leans out and starts erratically popping. Only, in your case, the leak is a big one at the intake, and only on the driver's side. And the engine continues to run ok, 'cause the passenger-side bank is working fine, and you only get some popping and no heat on the driver's side. You're getting a whole lot of air there, and not much fuel...but enough to let it ignite intermittantly. I wonder if the heads were milled, or for some other reason, the intake doesn't fit good now. Managed to get it sealed on one side only. Maybe just a bad gasket. Good luck.
I had one of those on a 351W, drove me crazy until someone came up with the idea. I had another distributor on hand, switched it and it was fine.
I would first adjust the valves and see if there's any difference. It could be a tight valve that was suggested in a previous post.
Running cold on one bank sounds very odd. Here are some ideas: Dual plane intake restricted on one side, bad lifters or cam lobes on one side, bad plug wires one side.
Sounds like it is time to pull the heads and cam and check everything. Hopefully the builder did ok on the bottom end/rotating assembly. Good luck, and keep us posted.
That would affect both banks, but good to bring up.
dual plane intake would affect both banks. one side of the carb feeds the center 2 of one bank, outer 2 of the other. A single plane can/will affect one bank.
My guess is that between the machine shop and the customer who assembled, there are 2 different heads (easy on Fords, they kept changing) and/or the driver's bank has valvetrain issues. Either the valves were sunk more on that bank and they didn't adjust the installed height, the rockers don't match, or the pushrods are a bit too long, hanging up the valves slightly. A flat cam can do this too, but it's unlikely it would mess up all on one bank only. Since you have it on a stand, pop those covers and check the top end out. You should be able to use a hammer handle to press on the liter end of the rocker and get the lifter to bleed down. Make sure they all have similar clearance when bled down. eyeball the valvestem heights, they should all be the same. Check for exhaust rotaters and lash caps on both sides. See if all valves move about the same when running (flat cam).
Yup, something weird is going on and it will be a DOH! moment when you find it. Wires are a good start, even swapping the whole bank to the other may tell you something. I'd doubt a cam, but a lifter is a possibility.
Ford's old dist.s for thse motors were not the highest quality when new, and 40 years of wear doesn't help. Not only the bushings, but the breaker plate and the vacuum advance pivot can cause all sorts of issues, and check the breaker cam lobes too. Again, this isn't likely to f up one side.
I have checked the distributor and all looks and feels good . I am going to double check the firing order and even change to a 351w firing order and see what happens . The worst it can do is not start . If that doesn't work I will set the plug wires back to a 302 firing order , start the engine and take some carb cleaner ans spray on the carb spacer plate and the intake on the drivers side and see what happens .
I don't want to tear the engine head off till I search all the other places first . If I have to tear into the engine then I will have to call the customer because that will cost him more money in labor . This is why I am looking at all the other things that can go wrong before I break the bad news to the owner .
I will get back and post what I find out !
Thanks to all !
Valve guides..leaking at times
Looking forward to hearing the solution you hopefully get to.
I have a similar problem with my vintage bronco. Similar but a little different. I am hoping mine is the intake gasket.
It is SO aggravating when you can't source the problem and you know you probably ought to just rip into the engine but you think it might just be something dead simple on the outside at the same time...
Broken intake valve spring?
The lowest cylinder most likely bad one.I would guess exhaust valve is leaking on compression stroke putting gas in header,then at TDC when firing pops thur exhaust.
"Broken valve spring..."
That is a little bit of what I am afraid of on mine. I have looked them over and they look ok, but it might explain a "sometimes" problem.
Timing chain could be off a tooth or two
i have a points dist.if you want to try it.i put another one in my 302 thinking it was my problem but it wasn`t.it`s good i think with new tune up in it.pm me and i`ll bring it over.
If it hasn't been mentioned, check for a blown or leaking header gasket.
Nevermind, should have read everything first. goodnight now!
I did buy new header gaskets and replaced them but no change . The gaskets were leaking so wasn't a part I didn't need .
I have checked the valve springs and none broken .
All rockers are non adjustable and tighten down .
Checked the timing and it's a 302 cam .
Plug wire are OK , I can hold them and nothing happens .
I rest the points and check them .
I set the timing to TDC for now .
I adjusted the carb .
Engine will start and idle OK 99% of the time but give it some gas slowly and it pops off and on out the drivers side header .
I did another compression test and I still have 3 cylinders lower on the drivers side lower than the 150 the rest have . They are 130 on #7 and 140 on the #6 & #8 cylinders .
The intake gasket is good at that side because there is dust laying on the area where the intake and head go together . If it was leaking there that dust would be gone !
So this is everything I have done today with the engine . The engine ran for about 15 mins today and temp gauge ran to 150 degrees . The hotter it got , it seems that was the more it popped out the header when I gave it gas slowly ! If I just nailed the throttle it would pick up just fine with no popping ! If I increase the throttle slowly then it pops !
I am looking at internal problems but don't want to tear into it if it's something else . It's a customers engine so he is paying the bill but I am not 100% sure what it is causing this problem .
The header is a little hotter now since I got the timing , points and carb set where it should be .
Thanks to all for the help and ideas so far !
I'd still be looking for a vacuum leak, just because the intake gasket seal looks good on the top doesn't mean it's good on the bottom. Any plugs missing from the intake? a cylinder with 130 lbs of compression will still fire, don't be so quick to assume that low cylinder is the root of all these problems. Remember you have FOUR cylinders that aren't firing at idle, not one. As mentioned before, at idle a small vacuum leak has a lot more of an impact than it does at higher RPM's. If you think it's the spark going away on four cylinders, you can diagnose that real easily, one cylinder at a time, with a timing light that uses a plug wire clip-on sensor.
what brand and what type of intake manifold does it have ?? >>>>.
A few ideas I didn't see tried yet, in order of what I'd try...
1) Have you confirmed that the spark gaps are correct?
2) Get some of those fancy insulated plastic pliers and do an RPM drop test. Pull and replace wires one at a time and record the rpm drop for each. That may help you isolate the offending cylinder(s).
3) I missed if you tried to confirm TDC, but just try an additional 10 degrees of advance and see if it gets better. Maybe the dampner has slipped (or has the wrong timing tab installed).
4) Also -- and this is a hare-brained one -- if you're really curious try it with and without gasohol. It it's a borderline lean condition than the 10% ethanol mix should be worse.
It's a stock 2 bbl dual plan intake .
All new spark plugs that I gapped myself . Didn't drop one when installing either . When I did the compression test I did male sure the gap and spark plugs were good and they were all clean !
I actually timed by ear then went and then put a timing light on and it was 1 degree off before TDC .
I understand about the vacuum leak . At idle it's 99% OK . Give it some throttle and it starts popping when it feels like it ! The #7 cylinder is the main problem .
I don't think I am loosing spark or it wouldn't backfire through the exhaust . I am just thinking it's either a bad intake gasket or a bad exhaust valve .
I did consider having the engine running at idle and taking a can of carb cleaner and start spraying the intake to see if the idle changes any .
Thanks for the ideas !
i don't think the compression readings you listed are the culprit. Generally a good engine will have all cylinders with in 10% of the highest cylinder. In your case that would mean 135 would be normal, you are just barely below that so I don't think that's it.
Put a video of it running up on You-tube and post a link here.
I have no idea what it might be.. but I still haven't seen you list any result of a vacuum test (maybe I missed it). Seems like the first and easiest test I would perform and it could tell you a lot about your engine.
I have had this happen, but it did NOT kill one whole side of the engine!
Weak Valve Springs. It would idle fine, but act up when accelerated. Popping, run rough, wouldn't "take the gas".
Again, the hard part of this deal is that it's affecting 4 cylinders all on one side.
That sounds like an intake that is not seated, valvetrain issues on one head or a different head that affects the compression on that side.
Rings, cam, intake, carb, timing, dist, should affect a single cylinder, all cylinders, or some on each side.
Separate names with a comma.