Ok so my 93 explorer 4.0l auto has 221k on it and runs like a dream up until a few days ago. I was driving to go fishing and cruising along at 50mph when all of a sudden it bogs itself down to a stall. It would idle ok while I was losing speed but when I pushed the gas it would starve itself. then it would not restart for about 40 min until after it cooled down. My initial thought was that my pickup coil overheated and that was the issue. So the next day I put in new plugs (was due for them) and it runs great. I drive a short drive shut her down and restart and now its misfiring. I replaced the pick up coil the next day, same issue. My neighbor is a mechanic and he brought over fuel pressure tester which came in at 33psi and held strong. Then we spent an hour running a computer on it and everything appears to be running normal (tps, o2 etc) however my misfire is still there.

Visual tach shows no movement sputters unless I rev it up high and let it come down, it will short sputter and then level itself off. Under load it sounds like a lawnmower. Its an old junker but right now its the only truck I have so I really need it running normal again!

I am lost and out of options. What could be causing this. The wires are good, plugs new, coil new, where should I check next. There are no check engine lights or any codes either!!!!!!

Thanks for any and all help gents!

 

Your valve seats are probably toast, the 4.0L OHV is know to have valve seats wear out, then after the seats fail, the head cracks. You solution, depending on whether or not it is cracked, is to either recondition the head with new seats, or to replace the head with an aftermarket one. Some of the better aftermarket ones already come with steel seats, so they are better than stock.

Alternately you could have a broken wire to one of the injectors, or a bad injector. The computer diagnostics on 4.0L prior to 1996 does not allow the computer to diagnose its own misfires very well, if at all. A '96 or '97 would be able to tell you exactly which cylinder was missing.

 

Khan,

Thanks for the info. Now if the head was cracked would it still run? I can drive it lately where ever I need just dont like the sound of it.

You are dead nuts on the diagnosing part. Although there were no codes we did try to communicate with the car, and it does not want to communicate with my neighbors snap on scanner (that made him mad all right lol).

On to the valve seats, I have never attempted such a job, is this something that requires a lot of tear down. Are there any other symptoms to that of the valve seats that I could look into to confirm.

Thanks again

 

The 93 is an OBD1, so it will not comm with his "SNAPON"..

Use a basic vacuum gauge connected to an unregulated port....

Vacuum gauge, the wonder tool
http://autospeed.com/cms/title_Using...3/article.html

 

I am aware of the OBD1 but he had the attachments for it. after connecting to the connection under steering, computer led us to EEC connector behind engine control box. I dont really know much about the diagnostics so not sure how to run this vacuum test. He just went home and grabbed all his ford adaptors and pulled the one required for the car.

 

Yes, a n engine with a cracked head will continue to run, but the performance will be penalized, depending on the severity and location of the cracks.

Valve seat replacement requires removal of the cylinder heads. To do that all of the intake components need to be removed from the vehicle, fuel rail, etc. The exhaust manifolds also need to be removed from the head. I've just left them attached to the rest of the exhaust. Then the heads need to be taken to a machine shop. They will inspect them and let you know whether the old heads can be repaired cost effectively, or if you need new ones. On both my 4.0L, the repairs would have only been marginally cheaper than new heads. Bad cracks are usually not repairable. If the misfire is not addressed, it can overheat and melt the catalytic converter, and when that happens, you will also have a severe drop in performance.

 

BEFORE you jump the gun and think bad valve seats, cracked head, etc... you said you just changed the plugs, and NOW are getting a misfire. start there, i cant tell you how many brand new spark plugs ive had be defective. did you gap the plugs before installing them? my bet would be you have a bad connection on one of the plugs, or a bad new spark plug all together.

 

Money pit,

the misfire started a few weeks ago but was intermittent. I was due for a tune up and while driving it would go from a misfire and then clean up mid acceleration and be fine. Then it went away for a few weeks. Thats when it bogged down the one day to a stall and would not restart until it sat a little while. I then through my new plugs in autolite platinum gapped at .054. After installation the misfire was completely gone. I drove not even a mile to a friends and was there a few hours and when I left and started it the misfire was there again, and has been ever since. One thing I did forget was that after it bogged out during that drive, I had a lot of air come thru the fuel bleeder. I had atleast 5 gallons of gas in the tank at the time so not sure y it filled up with so much air.

The truck itself has many issues cosmetically and mechanically and is used usually as my boat hauling truck. Right now its the only vehicle I have. The exhaust is cut after the cat and has been since I bought it 18 months ago. I paid 300 bucks for the truck and it has got more then my money back but now im too broke to buy a new car right now as I just bought a house.

I also feel its not the heads or valve seats bc its ran just fine for a long time. I also am not blowing any smoke, or losing any coolant. I would think if the head was cracked this would be a symptom. I did think that maybe a injector is clogged or shot and ran some chevron techron through it before my neighbors computer confirmed the injectors were ohming normal. I have good spark coming from the coil and good fuel pressure as well. Besides the valve seats and heads, and maybe the injectors. Im not sure what else to look for. I have checked all visible vacuum lines and dont hear or see any off...Problem is if it requires a teardown to solve then the truck itself just isnt worth any money being put in.

sorry for the long resonse just wanna be clear in description

Thanks

 

But have you connected a vacuum gauge to the engine yet??

BTW, I had a similar issue that plagued me till I ran a thread chaser down all the plug holes, been 3 yrs since and no hiccups.... Philip

 

Aqua - No I havent. I personally dont have a vacuum tester but my neighbor most likely does, just waiting to see him. Where would I hook it up to test the valves?

 

Autolite Platinum, or Autolite double platinum. The 4.0L needs double platinum.

Almost every pre '95 head I have seen had cracks. Those that hadn't cracked still had severe exhaust valve recession by 150,000 miles. This is eventually going to happen. Will it leak coolant or blow smoke? Not a chance, the cracks do not extend into the water jacket, they are typically found between the intake and exhaust seats. The leak is enough to cause or contribute to misfires, but sometimes you won't have any obvious symptoms.

To check for cracked heads or worn valve seats, hook up a compression tester, and do both a compression test and a leak down test. This will tell you which cylinders are wear, and can help narrow down why they are weak. If you pass a leakdown test on a cylinder, the rings are seated well, the head gasket is holding, and the valves are sealing. If you fail a leak down, something isn't sealing. A compression test will detect all leaks. I know if you squirt a heavy oil into the cylinder, if the compression improves, it rules out head gaskets and valves, the heavy oil slows down leaks past rings. So if you add oil and repeat the test,and its compression is significantly improved, it means that cylinder has bad rings. If the leaks are not the rings, the oil does almost nothing. That means its either a head gasket, valves, cracked head, or cracked block. If there are bubbles in the coolant, or coolant is detected in the cylinder, that points to head gasket. If two cylinders next to each other have low compression, that points to a head gasket leak between two cylinders. All other results are either valves leaking cracked heads, or cracked blocks, or occasionally, piston damage.

I recently had four 4.0L motors pulled apart. A 94, and '95, and two '97 head sets. On the '94 one head had no cracks, but severe valve recession, so the valve weren't seating. The other head had two cracks, and the valves were severely receded. This engine had 230,000 miles. On the '95, both heads were cracked, and all the exhaust seats were severely receded. This motor had 203,000 miles. On the '97, bank#1 had one receded exhaust seat. Bank#2 had one crack and two receded exhaust seats. This head had 132,000 miles. The next set of 97 heads had 6 receded valves and no cracks. It had 158,000 miles. In it my opinion that nearly all OHV 4.0L engines start wearing through the factory seats around 120,000, and that by 150,000 - 160,000 miles all of the seats are worn out, and any life beyond that, they will run, but at decreased efficiency and performance.

The better aftermarket heads use a tougher cast iron for the head, and steel valve seat inserts, instead of the factory flame hardened iron seats. This makes the aftermarket heads good for 250,000 miles or more, compared to the 150,000 mile Ford head.

A vacuum tester is really only going to pick up intake valve leaks. Due to heat, its almost always the exhaust valves that fail. On all the heads I looked at, none of them had any problems with intake valves or seats unless a crack between the exhaust and intake was present. So I seriously doubt a vacuum test will reveal much.

 

Khan,

Thanks for the detailed response. That makes a little sense to me, Ford is known for having junk OEM parts and often aftermarket seems to be the way to go. I used autolite single plat. as that was what the autozone computers called for. Could it be possible that the misfire is being caused by the plug not being hot enough. Should I swap out for doubles and see if theres a change? The truck does burn some oil as well so maybe a hotter plug will help with that and not foul out so fast.

On to the cracked heads etc. If this was the case would it of been intermittent on and off before hand, and then finally possibly failed. I am really hoping its not that or im at a spot where its time to drive it til shes blown and scrap it. No way worth the money of swapping out the motor/rebuilding as everything underneath is rusted away from wonderful Michigan winters.

I know for a fact my neighbor has compression testings and I will get with him to run some tests on it and report back my findings. I will use your post as my guide when I am looking for answers.

Thanks again for the leads and I will post back when I have more info!

 

Running a hotter plug or a colder plug will cause problem you run the proper plug. These vehicles have a waste spark ignition system, so you have to use double platinum plugs. OEM parts are usually of very high quality, so to call them junk is incorrect. Even Ford supposedly "junk" head is good for 150,000 miles, and is really the only weakness of the engine, and often the problem goes undetected because the vehicle can often still run pretty well with a bad head.

If this problem occurred after changing out plugs, as opposed to changing out the plugs because you were having a misfire, I would suspect that a combination of bad parts or incorrect installation my be to blame.

By doing a compression test, you measure the "health" of the engine. And engine that cannot pass a compression test is not worth spending money tracking down ignition or fuel delivery problems on, unless the engine is going to be repaired first.

If the compression test comes back ok, your problem is either fuel delivery or ignition. You just have to diagnose which. Few modern technicians really know how to diagnose problems, but you only need three ingredient for combustion: compression, fuel mixture, and and ignition source. If you have a misfire, one of those three has something wrong.