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So I don’t really know where to say I’m at. I bought this 87 4runner, drove it 75 miles. Shut down on me when I took it out of gear to downshift on highway. Started a few times after and sounded terrible. Now won’t even start.
What I’ve done:
clean plenum and throttle body
serviced injectors with new connectors on 1 and 4
cleaned spark plugs
adjusted valves
checked compression cold: 145, 115 (also wet), 160, 155
cleaned most engine sensors and connectors above block
Supposedly head gasket was blown and repaired 500 miles before I bought it. New timing belt and water pump, distributor and plugs. Valves adjusted.
Im at a loss. Have codes 4 and 11, whereas only had 4 before my plenum teardown and rebuild. I have a scope coming in to inspect through plugs. But meantime, this starting sound indicative of anything specific to anyone? From my search, it’s familiar to bad timing and/or seized motor. I can crank the crankshaft manually, but it doesn’t feel rhythmically smooth if that means anything.
I wish i knew more about trucks status. But there were many potential issues when it broke down. Wet Oil was slung all over front end when broke down. I couldn’t find source. Cleaned and wanted to get running to dye it for point source identification. No water in oil that I noticed. Scratching for direction.
Heres the YouTube link to starting if the upload didn’t work
Pull the valve cover, locate the compression stroke for number two (?) The low compression cylinder. Apply a leak down test (air into sparkplug hole), to find out which way the air escapes..
I hear a pretty consistent "tap" in that cranking, it's not a good sound.
Yeh. I don’t think it’s a good thing. It’s pretty much what it sounded like after I broke down. So before I took it apart. The leakdown test is a great idea, and meant to do it before I disassembled. I will once I get the resources. I’m going to inspect through the plugs with a camera this weekend. I’ll do the leakdown test when I can get a compress. Assuming it’s not any worse internally than before it broke down, I guess the only explanation is it could have jumped a link? Chain guard looks fine.
A compression test tells you how well the engine can compress air.
A leak down test can show you the amount of air leakage and most importantly, where the air is leaking.
By hooking up compressed air to a cylinder and listening for air in various locations such as the intake, tail pipe, oil filler cap / dipstick tube, radiator, neighboring cylinder spark plug hole, etc., you can get a pretty good idea of what type of low compression failure you have.
... and most importantly, where the air is leaking.
By hooking up compressed air to a cylinder and listening for air in various locations such as the intake, tail pipe, oil filler cap / dipstick tube, radiator, neighboring cylinder spark plug hole, etc., you can get a pretty good idea of what type of low compression failure you have.
Without a few prior leak-down tests, THIS is why you do one now. There is enough variation between instruments and setups that the "number" (a percentage) you get for a leakdown doesn't mean anything without an apples-apples comparison. In fact, you could skip the leak down tester and just provide air to the cylinder, but if you're going to that trouble you might as well set up the tester.
FWIW, there are lots of things that could be causing awful noises that won't be easily visible from the top of the piston. A bent connecting rod, a broken ring, a piece of something rolling around in the crankcase, a broken valve spring .... But you're on the correct path.
So I adjusted the distributor. Used scope to verify head 1 was at close to tdc and the crank at 5. Still no start, but was a smooth turn over at least. There was some backfiring. Plugs smelled like gas. I know this all means something and plan to research. Will update what I find. Thanks all!
And I looked keenly at the spring on cylinder 2 during tear down. Didn't look different from top from my unskilled eye. However, piston two may have a crack in it? Taken with my scope cam.
Stupid question. But did you verify TDC on Compression? A lot of people have made that mistake the first time, myself included. I pull the plugs and then put my finger blocking the plug hole for number one. If you have longer arms its pretty easy to turn a ratchet on the crank, you may need a partner to help. When i feel pressure building against my finger in the #1 plug hole I turn it just a bit more to confirm. Then remove my finger and I use the dipstick to find TDC. Just gently lower the dipstick until it finds the top of the piston and then when it quits rising your pretty much there.
Stupid question. But did you verify TDC on Compression? A lot of people have made that mistake the first time, myself included. I pull the plugs and then put my finger blocking the plug hole for number one. If you have longer arms its pretty easy to turn a ratchet on the crank, you may need a partner to help. When i feel pressure building against my finger in the #1 plug hole I turn it just a bit more to confirm. Then remove my finger and I use the dipstick to find TDC. Just gently lower the dipstick until it finds the top of the piston and then when it quits rising your pretty much there.
Yeah, and no offense taken here. I used my scope cam to check that the piston was near TDC, and I'm saying near because I set the crank to 5*, and it looked like had a smidge left to go til TDC.
What thefishguy77 is telling you is that there are TWO TDCs. One at the top of compression, one at top of the exhaust stroke. (The distributor, and the cam, turn once for every two turns of the crank.) If you set the distributor to point to plug #1 while the piston was at the top of the exhaust stroke, that's called being 180° out.
One used to be able to get a "whistle" that would tell you when you were at the top of compression, but since you only need to pick the correct revolution of the crank out of two, your finger on the plug hole should work just fine. I recommend using a straw or wooden chopstick to "feel" the top of the piston. A dipstick is pretty floppy, but if you used (say) a scredriver, one slip with the wrench could gouge the top of the piston.
By the way, your borescope picture does not look like a crack to me. It looks like the not-too-uncommon pattern of a really dirty piston head. That's probably not your problem, but if you get to the point where you've removed the head you'll need to remove all that carbon. It can contribute to knocking.
What thefishguy77 is telling you is that there are TWO TDCs. One at the top of compression, one at top of the exhaust stroke. (The distributor, and the cam, turn once for every two turns of the crank.) If you set the distributor to point to plug #1 while the piston was at the top of the exhaust stroke, that's called being 180° out.
One used to be able to get a "whistle" that would tell you when you were at the top of compression, but since you only need to pick the correct revolution of the crank out of two, your finger on the plug hole should work just fine. I recommend using a straw or wooden chopstick to "feel" the top of the piston. A dipstick is pretty floppy, but if you used (say) a scredriver, one slip with the wrench could gouge the top of the piston.
By the way, your borescope picture does not look like a crack to me. It looks like the not-too-uncommon pattern of a really dirty piston head. That's probably not your problem, but if you get to the point where you've removed the head you'll need to remove all that carbon. It can contribute to knocking.
So without taking the valve cover off, which I did before I understand that process when you can see the rockers, how do you exactly know if you are at top of compression or exhaust? I understand getting the "feel" of the piston, but how do you know if it's at the top of compression/exhaust? Assume your distributor is off and you have no help from the rotor.
I guess to add/clarify, with my camera, I watched the piston come up to the top, and it got just about alllll the way up to the top, I set it at 5* at the crank before it got there. I'm guessing if I had let go to the top the pulley would be at 0. Is it possible I'm still 180* off?
This is a great opportunity to learn to find TDC the foolproof way.
Turn the engine by hand, clockwise.
Watch valve movement on #1 cyl.
Intake opens, intake closes, then line up the timing marks for TDC or 5 to 12* before TDC if you are going to set the distributor with rotor pointing directly at #1.
If you observe the valve movement as you do this you will never be 180* off unless your chain has slipped dramatically, in which case it's not going to run anyhow.
Last edited by Melrose 4r; 05-13-2019 at 10:45 AM.
Yes. You saw the piston come to the top of the stroke, but which stroke? Compression, or exhaust? Just to be clear, the crankcase doesn't know and doesn't care which up-stroke is which. That is determined by the cam -- the valves are closed on the compression stroke, and the exhaust valve is open during the exhaust stroke. That's why looking at the valves is the "fool proof" (or at least most reliable) method.
But you have to remove the timing cover to do that. If you're not sure you're doing the finger-on-plug-hole method correctly (I don't find it very easy), you pretty much have to remove the timing cover to tell.
This is a great opportunity to learn to find TDC the foolproof way.
Turn the engine by hand, clockwise.
Watch valve movement on #1 cyl.
Intake opens, intake closes, then line up the timing marks for TDC or 5 to 12* before TDC if you are going to set the distributor with rotor pointing directly at #1.
If you observe the valve movement as you do this you will never be 180* off unless your chain has slipped dramatically, in which case it's not going to run anyhow.
I'd rather not have to take the valve cover off again right now? I did observe that when I had it off prior so I know what you mean. I certainly can if you're saying that's the only way to do it foolproof. But just to clear my thoughts here, the crank will reach 0 on the timing mark and every other rotation will be compression/exhaust. But if I can literally see the piston going up on a compression stroke, wouldn't that be TDC on compression when it reaches 0 on that stroke? And for an 87 22re, set it at 5* just before it gets to TDC? I assume this is to account for the counter-clockwise rotation the rotor makes when you key it in?
I'd rather not have to take the valve cover off again right now? I did observe that when I had it off prior so I know what you mean. I certainly can if you're saying that's the only way to do it foolproof. But just to clear my thoughts here, the crank will reach 0 on the timing mark and every other rotation will be compression/exhaust. But if I can literally see the piston going up on a compression stroke, wouldn't that be TDC on compression when it reaches 0 on that stroke? And for an 87 22re, set it at 5* just before it gets to TDC? I assume this is to account for the counter-clockwise rotation the rotor makes when you key it in?
yes, that's fine. I wouldn't advise you to start over. I thought you had the valve cover off. My point is only that if you watch valvetrain movement it's very clear, for any engine I have worked on, it's the same.
If you set timing marks to 0 and rotor directly to #1, you have no advance in the system. Engines don't like to run with NO spark advance. You will wind up having to advance the disti to 12* unshorted or 5* shorted to get it right. If you set the timing mark to 5* from the start, you are at 5* advanced. The car shows on TV make big dramatic moments out of flames shooting up through the carb when they first try to start it and have the timing off. It's easily avoided if you understand the whole cycle. Either way, check it with a timing light when you are running.
A lot of us can probably get a valve cover off faster than you can find your camera, locate a sparkplug socket and get a picture..
It's good practice for doing a valve adjustment if nothing else..
You find number ones compression stroke by watching or wiggling the rocker arms for the cylinder. They will both move slightly before touching the top of the valve.
You need to put some air on that low compression cylinder to find out where the leak is. The deviation is way out of spec, there shouldn't be more than ten percent difference between any cylinders. It's a serious issue like a bent or burnt valve, maybe a bad ring or crack, and best case just a damaged cam lobe.
05-10-2019, 05:48 AM
