1978 CJ with 304 V8, been running fine. Starts up from cold this morning. Engine is running at ~3,000 rpm to warm up. All is normal. Take foot off gas pedal. RPM drops and POW! A single loud POP is heard. The starter spins the engine, but the engine does not hit at all. No funny sounds, just smooth engine starting, spinning sounds.
Hit the carb with a little starting fluid and it will hit a few times and a distint 'whoosh' is heard intermittantly as the right front cylinder hits.
My diagnosis guesses:
1) Timing chain broke or skipped a notch
2) Fuel pump broke (but it was replaced about 6 months ago)
3) Intake manifold gasket
4) Head gasket
5) Exhaust Manifold gasket
More serious engine problems (broken piston, head, crank, etc) don't seem likely since there are no funning sound when cranking.
Oh great jeep wizards, What is it? What are the next things to do to diagnose it??
I would pop off the distributor cap and see if the rotor is turning.
That will quickly tell if the chain broke. You can also put the crank pulley on the timing mark and verify the rotor is still pointing at #1 wire in the cap to see if it jumped. (or the opposite wire across from #1.)
To check the slop in the timing chain, hand turn the engine to the timing mark with the distributor cap off. Then turn it back the other way while watching the rotor. As soon as the rotor starts turning the other way, look at the timing marks and see how many degrees of slop you have. Anything more than 15 or 20 deg and the chain is getting worn.
A pop can also be a coil exploding internally or an ignition module blowing a cap or something. I would be pulling a plug wire to see if I had spark.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
To check for a bad chain pull off the dist cap, crank the engine slowly by hand with a socket on the crank bolt and try to line up 0 degrees TDC on the crank and see if the rotor lines up on #1 cylinder. If everything turns and the timing marks line up, then it isn't the chain, if the rotor isn't turning, then the chain & gears are toast....$$$$$$$!
Most likely that's not the problem. Check the basics: Is it getting air? Is it getting fuel? Is it getting spark? Is it in time? If all of these are a "yes", then it should fire, but might not run if the carb is knackered. Al;so, this could be as simple as the + or - wires on the coil being loose, etc.
Take the primary off the coil stick an old spark plug in there then and hold it about 1" from the block and have someone crank it.
Off one notch would make your engine run like hell, but it would start. Fully broken and your engine would probably not even crank or there would be one hell of a grinding noise from the chain cover as the chain gets all wrapped up.
Pull the fuel line, crank, check for fuel. What your describing could be the fuel pump. Is it electric? Thought that old they were usually mechanical.
It would still start but run lean or stall
Would still start but run poorly and you would either get white smoke out the pipe (sucking coolant) and oil in the coolant.
Still would start, but make a "farting" noise. Sorta like a diesel running.. puffa puffa puffa
Not sure if the 304 is a non interference engine or not. That just means if the timing chain goes your engine will not eat itself by tring to comress an open valve. Very ugly.
I wouldn't suspect engine internals yet. Start with the electrical including the ignition circuit.
I'm sure that was intended to be "tongue in cheek", but as my Dad always told me: "The cheapest two things you can put in your cars are gas and oil." Of course, that was back "in the day" when I was paying 22.9 cents a gallon... but I think the axiom still applies even at current prices being an order of magnitude higher.
Good point but I bet we still have it cheaper than most Continents... $0.70/ lt average in Ontario Canada right now. Wonder what Dave Milne is paying in Scotland?
We pay 78.9p per litre, which @ 3.8 litres to your gallon would be 3 quid a gallon or rougly $5.50. We have not been hit so badly by the recent hike in gas prices because a) we almost started riotting the last time petrol went up b) the pound has strengthened against the dollar from 1.40 to 1.84.
Fortunately, my Waggy runs on gas [ propane] which is 1/2 the price of petrol [ gas :-) ]
We are paying NZ $1.14 per litre, which at current exchange rate would be roughly US $2.85 per gallon. That is primarily because of NZ dollar strengthening against US dollar, otherwise prices would have been a lot higher.
So was my reply, but I guess it was too early in the morning for humor. Should have added a :-) I burn 7 gal a day going back and forth to work. My wife isn't quite so bad, she only burns about a tank and a half a week. Unfortunatly, to move closer to work wouldn't save us any money, as the house payment would increase in size more than the money we spend on gas. At this point, anyway. If it hit's $2.50 a gal, we might reconsider.
-- Old Crow '82 Shovelhead FLT 92" 'Pearl' '95 Jeep YJ Rio Grande ASE Certified Master Auto Tech + L1 TOMKAT, BS#133, SENS, MAMBM, DOF#51
Indeed. European governments take ~68% of the price of petrol (in the UK, it is nearer 76%). Or put it another way, we have a 316% mobility tax. It seems hypocritial to blame rising petrol prices on OPEC for cutting production when governments are responsible for most of the price.
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