4.0 SOHC wont run right after timing chain rebuild - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 06-18-2015
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4.0 SOHC wont run right after timing chain rebuild

I had a timing chain failure on my 2001 ford ranger 4.0 SOHC engine. Removed engine and replaced all chains sp,sprockets guides, tensioners etc. Set timing, painted block , replaced waterpump and thermostat housing along with all new gaskets. Buttoned it all back up to find it barely running. checked compression to find drivers side , that hadnt lost time had two bent exhust valves with no compression on five and six. Pasenger side was all 150. had the head redone and put it all back together again. Now it runs really rough untill it gets to around 2000 rpm and then has light miss. Will not drive without stalling. Code thrown is Cam position sensor. / single sensor. Replaced both the cam position sensor and the Throttle position sensor. Had allready replaced the two temp sensors. Checked voltage at Cam sensor. No voltage. Checked and found continuity on the grey with red trace sensor wire. It still runs with cam sensor disconnected. It will also run the same with plug wires four and five removed and or switched. Runs the same with any one plug disconnected. cant find any shorted or messed up wiring anywhere. Also checked the blue with orange trace cam sensor wire at back of computer connection and still no voltage there or at sensor. I think that my PCM/computer may be toast. what does anyone think? Im at a lost and very frustrated with this engine system. I have never worked on an engine this complicated and hard to work on.
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Old 06-18-2015
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150psi is not great for a 9.7:1 compression ratio engine, expected at sea level would be 175psi.

But cylinder should still fire if above 120psi.

firing order is first thing
3 4
2 6
1 5
front

The 5 6 4 gets me almost every time.
So double check and then double check 4 and 5 wires, they are easy to reverse, at the spark plug end.


You will have a 2 wire Cam position sensor(CPS) on an '01, it generates it's own voltage and it will only generate voltage when engine is running, you should read varying(with RPM) AC voltage below 5 volts.
This is a Variable Reluctance sensor

The old 3 wire Cam sensor was a Hall Effect sensor, it had voltage from computer.

CPS does need to be timed with the cam shaft so it can time the fuel injectors and spark advance, a problem with the CPS wouldn't cause misfires, MPG would be down a bit but engine would run OK.


It was odd no one warned you about bent valves when a timing chain breaks, engines that use chains are usually interference engines(valves and pistons share space in the cylinder) so chain breaking while running means valves will be bent, period.
Engines using timing belts are usually non-interference so broken belt isn't quite as bad, but key word is "usually" my Chevy V6 has a belt but it is an interference engine.


Don't make it more complicated than it needs to be, all the added on stuff makes engines more reliable not less reliable, and sensors and controls rarely break.
The basic 3 still apply for a cylinder to fire.
1. compression, above 120psi
2. fuel, in 14:1 ratio
3. spark, at the right time.

Last edited by RonD; 06-18-2015 at 07:25 PM.
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Old 06-18-2015
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I thought 150 was good. I was checking voltage while running but I was checking DC. Ill try AC tomarow. This sensor has a magnet in it. Auto zone had problems matching it. They kept trying to sell me other sensors that looked nothing like mine. They finally found the match and said it was for a 2005. I havn't checked compression again on the newly redone head it may be higher. At least I can get at the plugs on the drivers side with only minor cursing. The passenger side is a bear on the back two. The firing order is correct at 123 and 465. Does seem odd. Is it possible to have the passenger side timing out by 180 degrees? I only removed the drivers side this time. Set the crank at TDC and set the drivers side cam normal with slot closest and parellel to the head with cam sensor up. Torked up the chain sprocket.
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Old 06-18-2015
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Firing order is 5 6 4

You said 4 6 5

You would have more bent valves if chains were out of time with crank.
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Old 06-18-2015
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actually it would be the drivers side that could be out 180 deg. The passenger side was set originally with TDC on crank and Piston One and Five at top and cams for those having valves closed. This time I only set the crank at TDC and didnt check the pistons or the other cam for a match.
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Old 06-18-2015
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The drivers side cam was set with the crank at TDC mark at Crank position sensor. does the crank turn twice for each cam turn? once for compression stroke and once for exhaust? That could get the two cams out by 180 degrees couldnt it? The valves should be OK just opening and closing on the wrong stroke? Ive been working on this repair so long im starting to confuse myself. I think I need to walk away and get my head straight. Maybe take up drinkin mass quantities of beer
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Old 06-18-2015
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I looked for bent valves on the passenger side head closer since that was the side that had the broken jackshaft TTY bolt for the lower sprocket. The drivers side never lost time since its chains were in tack, or so I thought. After I removed the that head again I looked closely and found a tiny cresent mark on the top of the two pistons that were effected. could just barely see it. The valves were closed and i did not do a leak test. on closer inspection the two exhaust valves were slightly open since they were bent.
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Yes, like most car and truck engines(including diesel), this is a 4 stroke engine, so crank turns 2 times for every 1 turn of the cam.

TDC mark does mean #1, and it's match #5, is at the top of it's stroke in the cylinder.

The cam is what determines the 4 strokes: intake(down), compression(up), power(down), and exhaust(up), by opening and closing the valves.

If you are starting from scratch then the TDC mark is just set at 0deg and you set cam(s) on their marks, when done piston #1 will be at TDC compression stroke.
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Old 06-19-2015
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decided that the only way it can be acting like this is for me to have set thwe driver cam at tdc exhaust not compression. So today I tore it down again and changed the drivers side cam 180 degrees off. Set TDC, took timing chain off, took cam loose to make sure all valves closed, rotated engine crank around again back to TDC. Put it all back together. It runs exactly the same as before. This thing is pure evil and playing with me. It starts and runs fairly smooth at 2000 rpm. put it in gear and it trys to quit. how can it possibleto run with the drivers side cam either on time or 180 degrees out. Still cant get a voltage from the cam sensor. It runs weather it is connected or not. No change. The only thing that changes anything is disconnecting the TPS or a major vacuum line, or the MAS. Im running out of things to try. It just stays in limp mode no matter what.
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Old 06-19-2015
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my coil pak sets right to left not for to aft. It is also marked where the wires attach to the pac.
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Old 06-19-2015
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At this point I think you are chasing your tail.
You are doing things that are making it harder on yourself, and the engine.

There is only one correct setup for crank, timing chains and cams, no need to wonder if it is right, just check it and be done with it.

I know "you know without a doubt" the firing order is correct, and this is exactly why you need to check it again.
And then check that #4 wire goes to #4 cylinder, and #5 wires goes to.....................
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Old 06-19-2015
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Yep. Checked the spark wires are on the correct plugs again. Traced them with my fingers as well as my eyes for the tenth time at least. My firing order is maked on the coil pak as well. 123 and four six five. I may just walk away from it for a few monthes and then take the engine out and start all over again.
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Old 06-19-2015
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1 2 3
5 6 4

Is correct, no matter what it says on the coil pack

1 and 5 are matched cylinders
2 and 6 are matched cylinders
3 and 4 are matched cylinders

Each pair is at TDC at the same time to balance the engine/crank

And that is what sets a firing order for any engine
1 4 2 5 3 6 is the firing order the computer uses, and since there are on 3 coils in the pack the "matched" spark plug will fire as well as the correct spark plug
1 4 2 5 3 6 becomes

1 4 2
5 3 6

when split in half, and you are now seeing the match pairs again

So 1 and 5 will always be on the same coil in the pack, and 3 4, and 2 6
So
[3 4]
[2 6]
[1 5]

Picture in post #8 here: http://www.explorerforum.com/forums/...d.php?t=303540

Last edited by RonD; 06-19-2015 at 02:36 PM.
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Old 06-19-2015
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had it running again and pulled 4,5, and 6 plug wires no difference. lots of spark at the coil pak but evidently not firing. also pulled number one which I know has 150 pounds comp at least and no difference either. The ol
nly ones that are evidently firing are 2 and three and sometimes one. will check compression on the new head again tomarrow. Ive got fuel pressure and lots of spark. There is either no compression for some reason or the timing is still off incredibly. hard to believe that I have no compression on a newly redone head. Paid a reputable machine shop $250 to get machining done with new seals and two new valves. With crank set at 0 degree mark, piston one and five up, both cams have offset slots closest to the block and parellel, cam sensor nub is up, all new chains,guides,tensioners, new tty bolts, new gaskets, new tty head bolts all torqued and twisted to specs. New thermostat housing with T stat and sensors, New waterpump, new upper gaskets, new Throttle position sensor, new cam position sensor, cleaned MAF, cleaned throttle body and IAC, all hoses checked for vacuum leaks, and all wiring conectors inspected for any problems. I'm at a loss. Maybe computer is not firing injectors? Fuel pressure is 80 psi. Code reader shows Cam Position Sensor and bank 1 single sensor? I erase codes and all lights go out. no check engine light or others untill it runs a while then back to the cam sensor code and check engine light. Im really getting tired of tearing this thing down to find nothing wrong. If I find compression loss again the whole engine gets torn down one more time. Its really amazing that it will start and run on two and a half cylinders.
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