This is interesting. I have codes P301-302-303, misfire cylinders 1-2-3 with rough idle. Runs well on highway.
Have changed plugs, and swapped ignition wires at coil pack with right bank, there are only three coils that are shared with right bank on the 4L engine.. So coil pack is not at fault.
Does not set codes when driving, only at idle.
Does anyone have any ideas on this one?

Thanks very much.

Mike

 

I would like to hear from anyone who has dealt with this problem
I have to repair this before June and the emissions test is due.
Thanks!

 

Jeeze this is an old one??

Yes, the waste spark setup would tend to eliminate the coil pack as the problem.

Fuel rail issue could effect injectors on 1 bank, have you tested fuel pressure, 65-70psi is spec on '02

4.0l SOHC could have loose timing chain on that bank causing compression issue at idle.
I would do compression test on all cylinders with all spark plugs removed for the test.

Have you pulled out spark plugs for 1, 2 and 3 and do they tell you anything?

Vacuum leak on bank 1 lower intake could cause it, it would lean out at idle causing misfires

 

Ron D.

Thank you for your reply. Yes this is an old one but now I must get with it and
fix this problem before June.
I am going to take your advice and do a compression test next and go from there.
Will let you know what I find. I did a fuel pressure test a while ago but will do it again.
Although this truck is a 2002, it is in excellent condition, four wheel drive, and has been heavily
rust sprayed with Crown so I would love to get this fixed and continue driving it.
Thanks again, will do the compression test this weekend.

Mike M.

 

4.0l SOHC had 9.7:1 compression ratio, that should test at about 175-180psi

Remove all spark plugs, so crank shaft can spin faster
Press gas pedal to the floor and hold it down when cranking, that opens throttle for air but also shuts off Fuel injectors so gas won't wash oil off cylinder walls.

If you can get a vacuum gauge($25), it can tell you alot about any engine, good tool to have in the box.
Read here on tests: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

When it says carburetor think injectors or intake manifold

 

Hi Ron,

I have a vacuum gauge, and the vacuum was normal the last time I checked it. I have also been searching for a vacuum leak but no luck. I had planned on pressurizing the manifold and then spraying all of the connections with soapy water but I would expect a vacuum leak would affect all cylinders. I like to think of the simple things first. I did have the problem with the rubber elbow leaking that connects the pcv valve to the manifold not long before this trouble began. Forgot to mention that my engine is the push rod model.
You mentioned the fuel rail for this bank so will check pressure again and have a closer look. Also, the rough idle and codes occurred quickly, not over time.

To troubleshoot this I am considering what is common to one bank of cylinders that would cause this problem, and cause it to happen quickly, not over time. And as I mentioned it runs fine when driving at any speed, and does not set any codes. Fuel consumption has not changed. (never been great with the 4L engine)

Thanks Ron for your help. I have to out this morning but will get started when I get back.

Mike

 

2002 would have SOHC 4.0l, so there was an engine swap to OHV 4.0l?

Did they stay with returnless fuel system, 65PSI?
Or add return line and use 35PSI?
Are the correct injectors being used, 35psi-'93-'97, or 65psi-'98-'00 4.0l OHV?

Did the computer get swapped or is the 2002 computer running things?

What about the CPS(cam position sensor)?
3 wire or 2 wire?
2002 computer would want a 2 wire.

Lower intake on 4.0l OHV was known to loosen up, it would only affect 1 bank if it loosened up on that side, upper intake leak would generally affect both banks.

O2 sensors are not used on cold start, they need to warm up to 600degF before they can accurately read Oxygen levels in exhaust, this takes about 5 minutes.
Do you get the misfire light during warm up or only after warm up?

Computer runs fuel mix based on factory parameters and Long term Fuel Trim in memory during warm up, this is called Open Loop.
When O2 sensors get warmed up then computer switches to Closed Loop and uses the O2 sensors to give it feedback on fine tuning the fuel mix.

If misfires only happen after the O2 sensors are on-line then I would swap them, the upstream ones, bank 1 to bank 2 and bank 2 to bank 1 and see if misfires move to bank 2.
And check the connectors for the O2s, they operate at low voltage, .1-.9volts, so even a small bit of corrosion can affect them.


Fuel injectors get 12volts when key is on, computer grounds each injector to open it, this 12v wire is daisy chained from one injector to the next, I would test the 12volts at an injector on bank 1 and wiggle the injector wires while doing so, you could have a poor connection that is affecting those 3 injectors.
Also check the 3 injector connectors, Ford injector connector tabs often break and get loose.

 

Well thank you again for your time and help!
Yesterday was a bust, but I am heading out to the garage next to get started.
I will start checking and testing the items you mentioned and get back to you to answer your questions.
I bought this used a few years ago so I do not know it's history.
Only that it was extremely clean, and has been running fine with no problems until now.
May as well bring out my laptop and monitor this site while I am working.

Mike

 

Bad News...
It is the dreaded 4L SOHC engine, an engine that has the timing chain tensioner design and manufacturing flaws.
I have heard rattling from the front of the engine now and then, but not continuously.

Mike

 

Just the tensioners and chain guides(cassettes) had the poor design, new design seems to hold up better on the older 4.0l SOHC.

But to my knowledge the chain issue wasn't responsible for misfires, usually just noise at first, and the 4.0l SOHC is a non-interference engine so valves and pistons can't ever touch even if chain jumps or breaks.
But because only one bank is affected I wouldn't take valve timing off the table, compression test would tell you if that was the case.

PCV hose elbows would rub thru on the bottom, this was a common issue on these engines that would lead to low RPM misfires, lean mix

 

Thank you again Ron
I have my Ranger in my garage and have started to remove all of the plugs.
in preparation for the compression test.
Had to go out to happy hour at a neighbors (GOOD) so had to stop.
Will be able to continue on the compression test first thing in the morning.
Will post the results then.
I do appreciate all of your help, you are very knowledgeable about the Ford 4L.

Mike M.

 

Monday update:
Before removing the plugs, I did a fuel pressure and vacuum test.
Fuel pressure: stable at 55 psi
Vacuum: 27 hg at idle

The plugs are all out so just waiting for my wife to come home so she can
crank the engine while I read the compression. Wouldn't you know it but I could
not find my 3/8 universal joint to use on the passenger side plugs.......

Mike

 

Your gauge doesn't hold pressure?

Make sure to get 3 or 4 "hits" before stopping the crank

Get the other plugs out before test if possible.

 

Yes my gauge is shot, haven't used it in years and the check valve parts are all missing...
So I borrowed one and here are the results:
(all plugs out, throttle wide open)
Left bank: 4, 5, 6 all are about 170 psi
Right bank:
cyl 1-130 psi
CYL 2- 130 psi
CYL 3- 90 Psi (two tests)

So there is the bad news. Major compression trouble on one bank. and CYL 3 very low.
I am assuming that the valve timing has changed, but why does it run
fine when driving and no codes set?

I forgot to say that all plugs are normal in appearance.

Mike

 

I feel that "misfire' is really an incorrect term for this issue.
The engine is idling rough due to the imbalance caused by low compression
on the right bank.
The ECM sensors interprets this as a "misfire" although it has nothing to do
with ignition.

 

Yes, Power added misfire, this comes from CKP sensor and the millisecond timing difference when a cylinder fires and adds power to the crank vs misfires and doesn't add power.
You could be falling in to this type by the lower compression not adding the same power so slight delay, #3 certainly would be misfiring now and then with below 100psi, the other two would just add less power to crank when they do fire.

Coil feed back, the ICM in the computer can detect a feedback pulse if there is a spark misfire, but it generates the same misfire code.

Runs better at higher rpm because compression increases.
Metal to metal seals, like rings and valves, are not air tight, they leak air/compression, the slower the piston is moving the lower the compression because air has more time to leak out passed rings and valves.
This is why you remove all the spark plugs, to increase crank/piston speed.

You could try adding a teaspoon of oil to each cylinder, then retest, compression will come up since rings are sealed better, but if it doesn't get up to 160+ then issue is valves or valve timing.

Could have a bad cam shaft on that side, it is wearing down, or chain is stretched throwing off valve timing, I wouldn't think it skipped a tooth because that should lower compression much more.

Could have even had a Lean problem on that bank for awhile and exhaust valves/seats are burnt a bit.

Leak down test could tell you if intake or exhaust valve is the issue, you can hear the air escaping when listening at tail pipe or throttle plate.

If nothing sounds bad then has to be valve train.

 

I did add some oil to cylinder 3, but it made no difference.
So tomorrow I will try a leak down test,will be interesting to see the results.

Might be worth the time to remove the valve cover and have a look for wear etc.
I see it is easy to remove the rear chain tensioner in order to see how much spring
pressure is being exerted on the chain.

Thanks again for all of your great advice. I plan on driving it until the emissions test
is due in June, and after that...?? It is a 2002, but it is in such great shape..frustrating
because I had to scrap a Montana van because of a head gasket failure. I just gave it
away and the person I gave it to had to remove the entire engine to fix it!
More flawed engineering...transverse engine, aluminum heads on a cast iron block......I better stop now....

 

Yes, don't get me started on aluminum heads on cast blocks, it's like not one engine designer ever took metal shop or basic physics, lol, metal expansion rates, duh.

Yes wouldn't be a bad idea to have a look, also see if there is "slop" in the cam, causing a delay in intake valve opening

 

Cylinder Leakage Test

I just did a CLT on cylinder 3, and it is only 10%.
Only leakage heard is at oil filler, so only hearing some leakage
through the rings.

No leakage was heard at exhaust or at throttle plate location.

May as well do cylinders one and two now.

Mike

 

Good work
Reading more and more like cam/valve timing issue, which kinda makes sense when whole bank is effected on this type of setup.

 

First time I have done a CLT it is very interesting.

So I think the next thing is to remove the valve cover and have a look.
Perhaps I will remove the rear timing chain tensioner first because it
looks like a quick job.

 

OK, the valve cover is off.
First if all what a nice clean engine...looks like the previous owner took good care of it.
So, everything looks fine, I even ran the engine and watched the cam and valves.
The timing seems to have good tension, so how could the valve timing change on this bank? May have to have a look at the front timing chains.
Next is to crank the engine to TDC and watch the valves and cams on number 1 cylinder, and read up on valve timing, perhaps there are timing marks on the cam or chain pulley I can refer to.

 

Good read here with pictures of SOHC timing chain setup: SOHC V6 Timing Chain Inspection & Repair - Ford Explorer and Ranger Forums "Serious Explorations"®

The Crank gear turns "Cam gear" via a short chain with 2:1 ratio, like an OHV engine.
But in place of the OHV cam is just a straight jack shaft that runs thru to the back of the engine, like OHV cam did.
This shaft turns the 2 overhead cams, one on the top of each head, via 2 longer chains.
Passenger side cam is driven by rear jack shaft gear, drivers side by gear behind main(larger) Cam gear.

So you have 6 gears(3 sets) and 3 chains.

I don't think Ranger 4.0l SOHC had the balancer shaft which can be seen in this explorer disassembly: SOHC V6 Timing Chain Parts Removal Procedure - Ford Explorer and Ranger Forums "Serious Explorations"®

And just for clarification for those that might read this, SOHC(single over-head cam) refers to 1 "cam" opening and closing both intake and exhaust valves, so even though there are clearly 2 "cams" on this engine it is still referred to as a Single cam.
DOHC(dual or double over-head cam) refers to engines that have separate intake valve cams and exhaust valve cams, so a "V" engine DOHC would have 4 "cams".
DOHC allows for better valve angle/placement in the head and also 4 valves per cylinder

 

Thanks again Ron. Have just gone through the procedure. If I am reading this correctly, there is no key-way on the camshaft sprockets.
How could this be built this way? The sprocket is held on the camshaft by the sprocket bolt only!
The right bank chain is tight and the tensioner seems fine as far as I can tell. I hope to have the camera tomorrow so I will have a better look down there. So if the camshaft sprocket has no key-way, then is this what has slipped. It just seems so improbable that it would have no key-way because any major slippage would cause serious valve and piston damage.
So I will be back on this tomorrow morning.

 

Yes, I see that, must be a reason for no key or pin, but I can see it???

Found some other pictures here: http://www.fordrangerforum.com/proje...e-rebuild.html