A few weeks ago my bronco ran fine it starts one morning no issue (it would start at first and then I would stop pumping the gas and then it would die so I just restarted and it ran fine) the next morning I go to do the same thing and on the second start it stops having any hood up firing up, just turning over. It’s definitely getting fuel and spark. Brand new distributor with coil, new plug wires, new plugs (the old ones had a lot of carbon fouling and a few were extremely gritty with a lot of buildup, I’m hoping the grittiness is not from metal), 3 month old carb which I’m sure isn’t issue. After these changes it now will backfire but not start(I’ve been using fuel and starting fluid but they both seem to have the same effect), it has started fires in the engine and shot flames out of the carb, I’m sure I put the distributor in at TDC on compression cycle and sure I have the correct firing order. I’m stilling trying to mess with getting the timing good but no matter where I turn it it either doesn’t do anything but turn over or it backfires as I mentioned. I’ve now spent a good amount of money and time and I just can’t seem to find the issue. Any ideas on what this could be?
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Desperate for some help trouble shooting engine problems, won’t run 302
- Thread starter Connorw
- Start date
I was looking at that too and i didn’t jump a tooth because when I put it to top dead center my old mark still lines up, and compression test is about the only thing that I can think of that’s left but I would think it should be getting compression because it was running as usual and then it just wouldn’t start, it wasn’t backfiring or missing on the first start
Also forgot to include it’s a 71 302 out of a mustang, I can’t guarantee but I believe it was rebuilt before I got it because when I changed intake out to 4bbl the gaskets looked in great shape and pretty much new even after driving with them on for at least a year, even my exhaust manifold gaskets looked pretty decent and my header bolts appeared rusty but came off great and some were even loose which didn’t make sense considering how beat up they look. The only upgrades I know the engine has is intake, carb, and lifters everything else appears stock
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Mmmmm......
Basic diagnosing 101, what is the fuel pressure to the carb?
Any chance you can get a timing light and keep it running long enough to set timing?
Backfiring through carb to me, is bad timing. And or far to much fuel, which could mean to much pressure.
I'd say you need to check timing, then carb, even though you think you know it's good, as in new, that does not mean it's good.
So, Fuel pressure, then timing (set tdc)
Basic diagnosing 101, what is the fuel pressure to the carb?
Any chance you can get a timing light and keep it running long enough to set timing?
Backfiring through carb to me, is bad timing. And or far to much fuel, which could mean to much pressure.
I'd say you need to check timing, then carb, even though you think you know it's good, as in new, that does not mean it's good.
So, Fuel pressure, then timing (set tdc)
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I could also be an unrelated valve train issue. Which would probably show up with either a compression test, or a visual under a valve cover. Things such as broken rocker arms, or studs, or bent or dislodged pushrods come to mind.
As does cam lobes going flat.
How long ago were the lifters replaced? And did you do it, or someone else?
As does cam lobes going flat.
How long ago were the lifters replaced? And did you do it, or someone else?
Hi, if you have an original style points and condenser ignition system I would get a couple of quality or NOS condensers. You would have the same symptoms if the roll pin on the distributor shaft is sheared, but you say the timing marks and the rotor are in alignment. Good luck
Lifters were replaced 4 months ago and I did it myself, I did it because I heard a tap and I thought it could be a lifter but it turned out to be the fuel pump
I’ve never had a condenser, my new distributor is hei idk if that makes a difference
I haven’t checked the fuel pressure yet, but the pump is mechanical and less than 4 months old and the fuel filter is 2 months old and might be dirty but I doubt, the carb is definitely giving plenty of gas when I pump it and when it just turns over it doesn’t give a lot of gas
And I definitely have tdc set correctly on compression stroke
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Age matters not, proof of what it does or does not does matter. Simple check to verify fuel pressure then move on. Confusing comment, it gives plenty of gas, except when turning over?
I meant that it gives the correct amount of gas at idle and when I pump the gas a lot comes out, it acts as it should
OK so I'm a bit confused so help me out......Did the issues start before throwing the new parts at it??
That's good......to much fuel maybe?? You mentioned your plugs were fouled.
OK just curious how you're sure??
When you installed the plug wires you set the firing order counter clockwise?? Sounds silly but have known many to make that mistake including myself.
Also, check the distributor gear. There's a shear pin that can shear off and turn intermittently if at all.
Good luck with this and definitely post up the cure once you figure it out!
Issues started before new parts, wouldn’t start all of the sudden so I adjusted timing started backfiring out of carb. I’m the past I’ve had a good amount of vacuum leaks and other issues which caused me to change fuel mixture and idle so that is likely the cause. I’m sure it’s not the carb because I checked it visually and everything was intact along with taking it off and everything worked as it should. Firing order is definitely correct and counter clockwise. The distributor gear on the old and new both look correct. I think my next step is to test compression but I doubt that would changed since it started and drove great the day before. My timing is definitely off because I’m still trying to adjust but should be close enough with all the adjustments I’ve made to fire up.
Wild horse 75
Full Member
I’m thinking if you can’t now get your timing adjusted correctly you jumped a tooth or two on the timing chain. TDC of the piston will always line up at the timing mark unless you’ve broken the snout off the crankshaft. You would need to pull a valve cover and check when the valves open and close but if it’s only a tooth or two you won’t know without a degree wheel. The only way to know for sure is pull the timing cover and see if the marks line up on the gears. Or if you have nylon gear teeth they may have finally worn to the point it won’t run. Also assuming the new parts you put in are good and not doing any testing of them is not good. You have a problem. The new part may still have a problem. Or you may have replaced a part thinking it would fix it but never got the root problem. A new carb won’t fix bad fuel pressure or a plugged filter. A new HEI distributor won’t work properly if you still have a resistor in the power wire. All things that need to be checked.
yeah, sadly, it does sound like timing and if happened all of a sudden, that's a +1 on the possibile jumping of a tooth on the timing chain.
I would remove the pass side valve cover and watch the valves move and confirm how the TDC marks line up on the crank. I can't say it would tell you 100%, but it would be a first step and worth the effort.
If it's clearly wrong in relation to the crank, then you know and if it all looks good, then there's a chance it's just timing.
You could also test spark on all cylinders. If they are severely fouled, they aren't properly firing.
Also, timing chains don't really jump teeth do they? More the belts that do...timing chains just stretch. What happens if you turn the engine by hand backwards--can you feel how long before it grabs the cam? I'd bet there's a ton of slack, but same effect as jumping a tooth.
I would remove the pass side valve cover and watch the valves move and confirm how the TDC marks line up on the crank. I can't say it would tell you 100%, but it would be a first step and worth the effort.
If it's clearly wrong in relation to the crank, then you know and if it all looks good, then there's a chance it's just timing.
You could also test spark on all cylinders. If they are severely fouled, they aren't properly firing.
Also, timing chains don't really jump teeth do they? More the belts that do...timing chains just stretch. What happens if you turn the engine by hand backwards--can you feel how long before it grabs the cam? I'd bet there's a ton of slack, but same effect as jumping a tooth.
Wild horse 75
Full Member
Well I would say it’s not common on an in block cam engine it can happen. With enough wear on a single roller gear set you can get enough slack that it will slip. It’s especially true on nylon gear teeth since they wear down. Longer overhead cam stuff can easily jump once you loose tensioner pressure or experience excessive guide wear.
Was turning engine by hand and tried turning both ways, I felt no slack it immediately gripped
Wild horse 75
Full Member
There will be no slack that you feel in a breaker bar. There is no disconnect between the bolt on the front of the crank and the crankshaft. You need to see if there’s slack between the crankshaft and camshaft. You can do this by pulling a valve cover and get a valve open part way. Then rotate the crank in both directions and see how far you move the crank before the valve starts to move again. You could try pulling the fuel pump and looking through the opening as well. The other issue that hasn’t been mentioned yet is the possibility the balancer has slipped and giving you a false timing reading but I think if you are 100% sure the piston is at TDC and the mark lines up I doubt that’s the case.
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