Repalced Heads - now it won't idle, mis-fires like mad...

[elbow2342]

Ok I remembered some thing that happened to me once, that almost made me a mental case. engine was dropping a cylinder when running but every thing checked out . even compression tested good. After a few days of saying what the hell.I tore in to the engine and found a broken intake valve spring. it would close the valve good enough to give good compression reading just turning over with the starter but not with the engine running. Another time I installed a newly remanufactured FORD 302 only to find out that it had a bent valve stem, after startup." Bummer" ..Could it be that your valve springs werent shimmed enough to compensate for the material removed during the valve grindiing process.If not the hydralic lifter will over power the valve spring and keep the valves from closing . Just a thought. (just because somethings new) ELBOW

 

[RammaR]

The alternator tested out bad. However I don't think that is the root of this issue. We pulled each spark plug wire - one at a time - to try and pin down a misfire to a single cylinder and none eliminated the clunking / pinging. It appears to be across the board or multiple cylinders.

With that in mind, we pulled the valve covers again this afternoon and checked for proper valve / rocker / pushrod movement.

None of the springs are broken and the intake and exhaust valves are moving as expected for the firing order (1-4-2-5-3-6). No rubbing or strange noises either.

Some of the popping noises sound like they are coming from or echoing in the valve covers. I was thinking maybe gases are getting past the valve guide seals and into the covers so we turned the crank with the spark plugs in trying to could get it to reproduce some sort of noise - nothing.

What I'm not sure about measuring is how far the valves / rockers should move on each stroke. Like you suggested - maybe they are remaining open just a little. I'm not gonna put the valve covers back on until I can absolutely guarantee it's not the new heads.

Autozone's website has two different styles of heads for a '96 4.0 OHV. One says "heart" shaped combustion chamber and the other is "D" shaped. Any idea what the difference would be if the other style got put on by mistake?

 

[ranger7ltr]

I would expect to find the spark from the coil pack to be weak with low battery voltage.. that might explain wet, fouled plugs in all cylinders...Plus I would not think the valves have a problem since the compression across all cylinders is pretty uniform...

On the heads the main difference can be determined by the exhaust port size...The early, heart shaped combustion chambers have a larger, almost oval exhaust port where the later HSC heads have a port that is rounder...

Late head...

Early head...

The long block is an early 4.0 Liter ...

 

[elbow2342]

Sorry but I dont know of any differences in combustion chamber shapes but that sounds like its worth looking into. remanufactured parts can cause real head aches either because of shoddy work ,or misapplication of part numbers. parts houses will replace a bad part but its the mechanic who suffers. time loss, much frustration, etc.
another posabilility is that sometimes when cyl. heads are machined. you have to buy shorter push rods to compensate for material that was removed from the gasket surface. of the heads to flatten them out, they may have as much or more than .050 or.060 thousands of material removed and then your lifters may not compensate for the difference. one test is with one valve open intake or exhaust the push rod on the closed valve should turn easily by finger tip with out resistance.. dont give up elbow

 

[96eb96]

dynamic compression test may be worthwhile.

 

[jd4242]

The alternator tested out bad. However I don't think that is the root of this issue. We pulled each spark plug wire - one at a time - to try and pin down a misfire to a single cylinder and none eliminated the clunking / pinging. It appears to be across the board or multiple cylinders.

With that in mind, we pulled the valve covers again this afternoon and checked for proper valve / rocker / pushrod movement.

None of the springs are broken and the intake and exhaust valves are moving as expected for the firing order (1-4-2-5-3-6). No rubbing or strange noises either.

Some of the popping noises sound like they are coming from or echoing in the valve covers. I was thinking maybe gases are getting past the valve guide seals and into the covers so we turned the crank with the spark plugs in trying to could get it to reproduce some sort of noise - nothing.

What I'm not sure about measuring is how far the valves / rockers should move on each stroke. Like you suggested - maybe they are remaining open just a little. I'm not gonna put the valve covers back on until I can absolutely guarantee it's not the new heads.

Autozone's website has two different styles of heads for a '96 4.0 OHV. One says "heart" shaped combustion chamber and the other is "D" shaped. Any idea what the difference would be if the other style got put on by mistake?

the difference would not cause this,the head should be stamped,you should have 95tm heads.you can run 95tm 97tm and 98tm all have the same size combustion chambers 48cc but the 98tm have a more egg shaped exhaust port to speed up the velocity of the gases.the only head that would mess with the compression and may cause a problem with the pcm is the 90tm and 93tm heads,they are 60cc and would lower your compression to 8:1.you may have rebuild head that have been milled to much and causing you valves to stay up just a hair but your talking about a LOT would have to be milled.smith brothers makes a pushrod measure for $13 bucks.you can test what length push rod you would need and i have all the spec for all that but i do not think this is the problem.maybe a bad EDIS or maybe the short bar for the EDIS fell out,check it and all wires and voltage for that box,its behind the pass headlight if you didnt know

 

[jd4242]

also may want to go ahead and get a new coil pack just to make sure.its a 3 coil pack so 2 cylinders share a coil so if one is starting to go bad it may test ok but ever so often it goes out,that means two cylinders will fail giving a sound like yours.its only like $70 for an accel pack and will help performance,if its never been changed now is the time
http://cgi.ebay.com/ebaymotors/Acce...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

 

[RammaR]

Thanks for the info on the heads. The originals were 95TM's. I can't find a specific stamping on the new heads, but they are supposed to be new castings (aftermarket) and shouldn't have been shaved down any. I'm almost positive they had the same type of heart shape combustion chamber. I will be calling the engine shop tomorrow to confirm. If the castings were a little short, it would make sense that the pushrods were tight. I thought that was a great idea to try to spin them.

We tried rotating all of the pushrods, the intake on #2 was noticeably tighter than the others. After loosing up all three bolts and re-torquing at the lower end of the range it spins much better. I'm not convinced that was the issue as #2 cylinder had the best compression. But I think its a better condition now that it isn't under the pressure.

With no real tension on the pushrods, no broken springs, and proper valve movement with the firing order and TDC on the crank - I think I'm about comfortable again that the heads are not the root issue.

jd - I replaced the ignition coil unit about 2 years ago with a new Motorcraft unit. The primary coil was at ~0.7 ohms, while the secondary pairs were just a little over 12k-ohms. The Haynes manual says 6.5 to 11.5k-ohms. So that might be a little high, but not way out there.

It doesn't appear that '96s have a separate EDIS / ICM. Looks like it was a stand-alone unit on 1995 and earlier trucks. I do have the shorting bar (SPOUT connector) back on the firewall by the PCM. Disconnect that over the weekend made no difference, which is why I decided to open up the covers again. Removing the shorting bar takes the PCM signals out of the loop and reverts to firing at 10-degrees BTDC.

So at this point my next step is to start putting it all back together. Install a new alternator, fuel filter and plugs (for good measure). The battery is back at full charge and ready to go in.

Keep your fingers crossed and any new ideas coming...

 

[ironbow123]

ironbow123

hi, did you try to clear the onboard ecm (computer) try disconnecting the negative then the positive battery terminals for a few minutes, and just let the ecm re-learn everything, can't hurt to try it, and there really is no way to time your 4L everything is run by the ecm

 

[RammaR]

Thanks for all the help - got the Explorer running again!

It seems that the culprit was that the pushrods were a little too tight and holding open the valves. Elbow - your comment about turning the pushrods easily is what got us back on the road. The rod for #2 exhaust valve was always tight and a few others took a good bit of force to rotate. When I first put it back together I torqued the rocker arm assembly down towards the upper end of the Haynes manual range.

I pulled all the pushrods to measure them - they were all withing just a couple thousandths of each other - I put them back in but torqued towards the lower end of the range. As-left, all the pushrods would spin easily but there was slop in the up and down direction.

She fired right up and is back on the road!

Thanks again for all the input.

 

[elbow2342]

Im happy to hear you got your wheels going again . Be sure to keep your eye on the temp guage as overheating is usualy the culprit when it comes to head gasket failure,or cracked heads especialy aluminum because of the expansion and contraction rate as the metal heats and cools. Glad to have helped. Elbow