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

(YouTube) Replaced Heads - now it won't idle, mis-fires like mad...

I've got a '96 with the 4.0 OHV engine with 187,000 miles. I just replaced both cylinder heads - one was cracked pretty bad, water leaking into cylinder 6 and smoking out the tailpipe. The other side was better but looked like it might have some cracks forming so I went ahead and got two rebuilt heads.

Just finished putting everything back together and when I fired it up, it starts ok and then quickly coughs / sputters / knocks as it tries to idle and then dies. I don't hear a vacuum leak and all the electrical connectors are back together. I can give it gas to keep it running at about 1500 rpm, but it's still not running smooth.

The engine is vibrating more than i've seen it before and there is a clank / pinging sound coming from the passenger side cylinder bank. The push-rods and rockers all looked to be in pretty good shape - nothing bent or excessively worn. I was pretty careful when putting them back in to make sure they were in the sitting in the lifters.

Any thoughts on what to try or look for before tearing back into it? It's definitely not drivable as is and I need to get it back on the road soon with the snow.

Thanks in advance.

Did you mess with the timing,or cam sensor

not sure if the rocker arms are adjustable or not but if they are, you might have them too tight. or you crossed the plug wires somewhere.

I rotated the crankshaft by had to inspect all the cylinder walls. I didn't removed the lifters but moved them each a little to make sure they were smooth. But no - I didn't do anything to the timing or cam position sensor. I may be bumped the cam sensor a little when putting on the lower intake, but it wasn't removed or unplugged.

i thought plug wires too, and had my wife help me re-trace each of them to make sure they were correct. I'm thinking it could be something with the rocker arms - but i just pulled them off and put them back using the torque in the haynes manual - didn't do anything to them specifically.

I would double check the timing and plug wires then start looking for a vac leak.maybe a injector o ring.is it throwing a CEL?

actually, would a compression check help tell me if something was off in the valve-train?

no CEL yet - doesn't really run long enough to get one. I've got a basic code reader and nothing is showing as pending either. I ohm'd all of the injectors and they all were good at ~16.2 when I had the intake off. I did use new injector o-rings when I put them back in.

The timing isn't adjustable - how would i check it? the cam position sensor seems to be nearly un-reachable without major disassembly.

Pull the valve covers off,you could have a stuck valve or broken rocker,this just happen to me.

jd - how did you tell that the valve was stuck?

You can tell from a compression test,but I guessed

Ran the compression test this morning and all were within about 10-15%. The first crank pushed the need to about 90 psig for each cylinder and then it built from there. So it doesn't seem like a valve is sticking.

The idle was a little better this morning, but still rough. I'm wondering if it just needs to run a bit to smooth out. It blew a lot of white smoke out the tailpipe when it first started to clear out the water from when the old head cracked and there was water in the #6 cylinder when i opened it up. So maybe it just needs to blow it out?

I don't want to run it more and do damage though....

Here's the latest update on this ongoing battle: Explorer 5 - me 0

Compression test was ok. Pulled the passenger side valve cover and manually turned the crankshaft to make sure the rockers, pushrods, and valves all moved normally. They did - no obvious issue there. I didn't pull apart the driver side valve cover - since the other side was good, and i didn't hear any odd rubbing or clicking from either side while hand turning the crankshaft.

After putting it back together it would actually idle on its own (roughly) but it didn't need near constant gas to run. I heard a vacuum leak and traced it back to the egr tube where it slides up into the intake plenum. The rubber gasket there wasn't sitting right and allowed air in. So I took the upper intake off, fixed the rubber grommet and put it all back together - thinking that was gonna do the trick. Back together, no vacuum leak but it won't idle. It needs steady gas again. And it was trying to backfire out the intake.

I think the cat's are at least partially clogged, so I disconnected the fitting at the Y-pipe just infront of the cat and pulled back the tailpipe to reduce the backpressure there. It sounds like a racecar in the garage, but still won't idle. However it isn't backfiring out the intake. The path of least resistance is out that pipe now.

It really seems like a timing issue or fuel maybe. To swap the heads I had to disconnect the crankshaft position sensor, it tested out fine per the Haynes manual. 1.5 volts to ground and about .4 volts AC while cranking. The camshaft position sensor is at the back of the engine and I can't really get to it without removing at least the upper intake again. It wasn't disconnected or adjusted during this adventure. It's on the investigate list though.

My question now is: I rotated the crankshaft by hand while the heads were off to inspect the cylinder walls. I'm sure it wasn't in the exact same position when I put the heads and rocker arm assemblies. Could that have somehow thrown off the timing? I thought between the cam / crank-shaft position sensors, the computer automatically adjusted the timing. The valves are just going to go to the position dictated by the pushrods / camshaft - right?

I'm looking for suggestions - I haven't verified fuel pressure, i also am thinking of checking the pressure regulator. I've ohm'd the injectors - but also want to apply 12-volts to them to make sure they are firing properly the next time i have access to them.

Oh, the other thing we did tonight was to use an in-line spark plug tester to verify a signal to each plug. They all looked good, so I don't think its a wiring or ignition coil problem.

Thanks,

put a timing light on it,if its backfiring out the intake its got to be timing or stuck intake valve somewhere

It's a good thing I love this truck, its driving me nuts as I'm no closer to keeping it running. Here's a quick update of what we've tried over the past couple days:

Attempted to adjust / reset the timing per this thread. I was skeptical but it was worth a shot since it didn't require much dis-assembly - however it didn't have any noticeable impact.

Tested each of the fuel injectors with a 12-volt power source. They all clicked as expected. So they've passed the ohm and clickly tests.

checked the valve covers for positive or negative air pressure. I put a plastic bag over the end of the vent hose that comes off the oil filler neck on left valve cover and runs over to the air induction tube. I pulled out the PCV valve and put my finger over the hole to feel for the pressure there. The bag inflated and I felt some air being pushed out of the PCV hole. Definitely not a large vacuum there.

Used a boroscope to look down the lower intake passages (upper plenum removed again) to check for a gasket mis-alignment. All six passages looked pretty good - no gross mis-alignments. It seemed like the ports on the head were a little smaller in diameter than those on the lower intake - but didn't see a gasket issue.

I tried to get a timing light from my local Orielly's - they didn't have a loaner tool but said that with the the ignition pack, it wouldn't work anyway. They said I'd need an older style distributor for it be really meaningful / effective.

So I'm still stumped and this is going on 2+ weeks now. Fuel pressure regulator, massive (but quiet) vacuum leaks, or valve / head issues are still on my mind. The compression test kinda makes me think it's not a valve issue, but I've been wrong many times before.

When we pulled the #1 cylinder spark plug, I was shocked to find it black. Not oily - but black with soot / carbon. I put in new Motorcraft plugs with the new heads - so it doesn't have even a mile's worth of run-time on it yet. I'm tempted to pull the other plugs to see if its similar across all the cylinders but ran out of time tonight.

Please keep the suggestions coming - I appreciate the help!

The explorer is still winning this fight.

EGR valve = OK
DPFE = OK
EGR regulator = OK
TPS = OK
IAC = OK / cleaned
CKP = maybe ok?

The Crankshaft position sensor is getting the 1.5 volts from the harness. However when I hook the voltmeter up to the sensor and crank the engine I get a fairly steady 0.3 VAC. It bounces a little but I'm not sure it's "pulsing". Has anyone else tested a good CKP - what where the results?

I'm still trying to get my hands on a gauge to test the fuel pressure, haven't found one locally yet.

suggestions?

Breaking news - all 6 (brand new) spark plugs are very black with carbon soot. They aren't oily, its fuel residue and they smell like it.

CKP sensor did check out OK. Maybe they're all sooty from the mis-fires, but I'm thinking its a fuel delivery issue that's causing it. I pulled the plugs hoping to see 1 or 2 all black and the others clean - thinking it would point me to something with those cylinders. But with them all black, it seems like its upstream of the cylinders / valves, etc.

Going to go try to find fuel pressure gauge again. As mentioned before, all 6 injectors pass the ohm and +12v pop test. Does anyone know if the fuel pressure regulator fails, what the pressure would go to? If it fails low (like a weak pump) then it wouldn't explain much. But if it fails high, then it could explain the extra fuel.

The fuel pressure regulator is a little weak but working within specs. Here is a YouTube video of the issue:



At low rpms, it sounds like it wants to tear itself apart from the inside out....

I take it that poping sound is it back firing through the intake.did you ever put a timing light on it?have you cleaned your egr?running out of things to test

jd - Orielly's said I couldn't use a timing light on it since it doesn't have a distributor. They sell a $40 and $120 light but said neither would work.

We did unplug the "shorting bar" near the PCM which puts it to its base timing mode, eliminating the computer control. No luck - died just the same.

The EGR valve is clean and passed the vacuum check. Holds vacuum fine and I can hear the diaphragm click up and down with / without vacuum.

Vacuum gauge connected to the manifold spools up to 18-20" right away and then falls to the single digits and bounces as the engine chokes off.

I'm assuming that popping noise is backfiring through the intake.