Scratching head after installing new heads. (Sorry for the pun)

[1991ExploderXL]

Ok here goes, stock 1991 Explorer XL, ran well, has noticeably lost power, using coolant between every trip.

Truck belongs to my Dad, he says "crush it" I say "NO WAY!"

I tore it apart and $1,300 later I'm reassembling it. I cleaned and lightly oiled the lifters, no priming and I also bottomed out the piston in the lifter by depressing the check valve slightly and running each piston to the bottom of its bore. I did that in hopes on allowing the oil pressure to build and set the clearance properly. The pistons in the lifters were sitting on the spring in the very bottom of the lifter.

Fast forward to yesterday evening, everything is buttoned up and reinstalled. I filled the manual for every step. Cooling system held 12psi of air for over 5 minutes so I know it sealed up nicely.

I go to crank the truck and it will only spit and backfire. Oil pressure builds according to the gauge in the dash. But the truck refuses to start, I have heathy spark (tested with HEI spark tester, and I have healthy fuel flow. (Fuel pump and fuel filter are less than 2 months old. Fuel injectors were professionally bench cleaned yesterday and flow matched) I check compression and I have two cylinders at 0psi, two at 30psi and two at 65psi. I decide to tear it back down to the rocker arm shafts and I notice that the rocker arms are all virtually level. I'm guessing that the low comps are due to the fact that that I basically installed the lifters in a "collapsed" state and the spring under the piston is taking up the force from the cam instead of transferring the force to open the valves.

Anyone have a suggestion? Thank you in advanced.

 

[Rick]

Yes, the lifters need to be "primed" before installation. I don't know if they will be able to pump up on their own.

 

[1991ExploderXL]

That's what I suspected, I work on OHC bike engines a lot but this is (somewhat obviously) my first pushrod engine headgasket job.

Any thoughts on pulling the rocker shafts and trying to pump the lifters up in the block maybe while cranking vs dropping $200 on all new gaskets and bolts?

I'll do whatever it takes.

 

[974X4BLACKSPORT]

I have been building engines for years, all with hyd. camshafts, here is how I have always primed the lifters, I take my oil squirt can, stick the tip in the hole in the side of the lifter and squirt oil right into the lifter, after about four pumps of the oil can trigger, 10W30 oil is coming out the top and side holes of the lifter, instant primed lifter!

 

[1991ExploderXL]

I have been building engines for years, all with hyd. camshafts, here is how I have always primed the lifters, I take my oil squirt can, stick the tip in the hole in the side of the lifter and squirt oil right into the lifter, after about four pumps of the oil can trigger, 10W30 oil is coming out the top and side holes of the lifter, instant primed lifter!

I thought about that and I don't have any issue doing that if needed. Just want to make sure there is no way to prime them in the engine as I've already installed the new head gaskets and torqued the bolts.

Question though, do you hold the upper cup where the pushrod sits to prevent the oil from pushing it up and out of the lifter while priming it?

 

[974X4BLACKSPORT]

The best way to prime your lifters after they are installed in the engine is to crank the engine over with the starter with no spark plugs installed, a mechanical oil gauge connected to an oil gallery will let you know if your getting good oil pressure when cranking.

 

[1991ExploderXL]

Ok, I'll definitely do that. Would it help to loosen the rocker arm shafts some or can the oil pressure overcome the valve spring tension? Thanks for your help and insight!

 

[974X4BLACKSPORT]

Dont loosen anything, except remove the spark plugs, disable the fuel injectors and ignition system, you just want to spin the engine over so as to pump oil into all the oil galleries and moving parts, should not take all that long, even thought the load on the starter will be light, dont crank more than 15 seconds at a time to reduce over heating the starter.

 

[1991ExploderXL]

You are the man, I'll try this procedure this afternoon. Thanks so much! I'll report back later today.

 

[1991ExploderXL]

Well I've cranked the engine over for about a minute total today. Five or six separate 10 second bursts then I go and do something else. My comps went from 0-0-30-30-65-65 to
35-45-50-65-65-90. I can definitely see a difference for the better but still, only one cylinder is making good vacuum at the intake manifold. It's about 55 degrees in my shop and the starter is cranking the engine at a fair speed, battery is about 2.5 years old so I'm recharging it in between bursts to get the RPM as high as possible. I found the distributor plug left over from the 2.9l today and I'm debating trying to prime it with a drill.

If the engine would start as is I'm pretty confident that the oil pump and the reduced viscosity from warm up would pump the lifters right up. It has Valvoline 10w-30 full syn high mileage in it now which probably doesn't help, I'm switching to the same type oil in a 5w-30 as soon as I get it running in an effort to get oil to the valvetrain sooner.

 

[1991ExploderXL]

Ok, new development! Out of curiosity I tried my rigid compression test adapter instead of the flexible rubber hose adapter I had been using. Compression went from 30-55 on the forward two drivers side cylinders to 190-210!!! I think old rubber flex hose in my compression test set is getting tired! But thankfully it appears as if my lifters have pumped up! I'm going to fabricate a shorter rigid test adapter to check the other 4 cylinders which are much tighter clearance wise in the engine bay. If they all blow well, within 15-25% of the two I got good readings off of earlier I'll slap the valve covers back on along with the upper intake manifold and try to light it off again. Thanks for all the help and time guys, I really appreciate you knowledgeable folks chiming in to lead the blind!


In the pics you'll see the offending rubber test adapter on the left and the rigid metal one on the right.

 

[974X4BLACKSPORT]

There must be a blockage in the rubber hose, restriction possibly, try blowing air through it. Those cranking compression numbers look real good for an OHV engine.

 

[1991ExploderXL]

Either a blockage or the rubber O-rings aren't sealing well against the tapered spark plug ports. It's hard to get the rubber hose snugged up as where the wingnuts in the metal adapter make it easy. I'm glad to hear the numbers look good, what is the ballpark average for a healthy 4.0l OHV? I looked in my vintage Chiltons manual and it just stated that the numbers should be within 15% of each other. No actual cranking compression spec.

 

[974X4BLACKSPORT]

The reason the manual doesn't give a number because the actual number is not what is most important, consistency is whats important, you want all the cylinders to be as close as possible. There are a lot of variables that can effect the cranking compression numbers of the same engine, a weak battery or starter can result in low numbers, so can leaving the throttle blades closed. I can only guess what the OHV engine should be, I was thinking in the 150 - 170 psi range for a healthy engine, but again, consistency is key.

 

[1991ExploderXL]

Roger that, my numbers this evening are without the upper intake manifold on so the variables associated with the throttle body, throttle plate position and losses/turbulence from the upper intake plenum may have contributed to the higher than typical cranking numbers. I'm also keeping the battery on charge at all times except when cranking so that I know makes a difference too. When I get back from work tomorrow I'll have a chance to test the other cylinders and hopefully they'll test high as well. If so, I'm going to put her back together and hopefully spend a little more time behind the steering wheel instead of under the hood!!

 

[1991ExploderXL]

Ok, here's the latest! I just sealed everything back up, verified valvetrain is moving now. Lowest cylinder is 165psi, highest is 190psi, all measurements are with the engine cold.

I reconnected everything and tried to crank it up only to get the same result, it will pop and backfire like the timing is off. Never even tries to start. That's it, throttle position makes no difference. Just wondering what in the world could be going on here? Only thing I can come up with now is maybe some of the water I cleaned the fuel rail/center intake manifold with is still in there and causing the engine not to start. I have compression, I have spark (not adjustable) and I have wet plugs...

 

[1991ExploderXL]

Is there any kind of ignition or TPS relearn procedure after having the battery disconnected for 3 weeks?

I'm going to see if I can disconnect the fuel return line somewhere relatively convenient when I get back to the shop and purge the fuel rail to look for signs of contamination.

 

[~X~]

This might sound pretty basic but, have you double checked the firing order?

Is it backfiring through the intake?

 

[974X4BLACKSPORT]

Try this, get a can of starting fluid and givve a good squit down the throttle body, immediately try to start it, if it starts and then dies you have a fuel problem, However,, the wet plugs wont fire and may now be fouled any way.
Also, double check your plug wire routing (firng order).

 

[1991ExploderXL]

Hey guys, thanks for the feedback. I triple checked the firing order against the info in my chiltons manual. I'm going to look online to make sure that info isn't wrong.

I did try the starting fluid method, loosened the intake tube where it attaches to the throttle body. Gave it a small squirt of brake parts cleaner (throttle wide open) aimed toward the back of the intake manifold then tried to crank it. It backfired out of the intake hard enough to blow the (not tightened) intake hose off the throttle body with a ball of fire. That's what makes me wonder if the timing is off somehow. I know it's DIS, any idea where the SPOUT connector is?

I'm guessing that I have overlooked something simple. I'll keep digging