Hi guys,

I was having some problems with the engine consuming coolant, oil/coolant contamination, and an intermittent leak at the front intake manifold gasket, along with intermittent warm surging and stumbling at startup, suspected loss of power, and poor fuel economy.

With these symptoms, I disassembled the engine, discovered the driver's side head gasket and intake manifold gaskets were bad, and replaced them with new gaskets. (Fel-Pro Head Gasket Set HS9111PT).


Driver's Side Cylinder Bank - Blown Head Gasket


Initial Engine Teardown

As I've said in multiple other posts, the truck was not maintained in any way, shape, or form, and the engine's condition certainly does not reflect the odometer at just under 71,000 miles. Unfortunately, I am moving in less than two weeks, making an engine swap not immediately possible, forcing myself to spend the time and effort (seven 8+ hour days in the Georgia heat with a heat index of over 100) to repair the original 3.9L LA. The vast majority of time was spent cleaning both heads, intake manifold, all gasket mating surfaces, and sludge buildup with a razor blade, parts cleaner, and degreasers. At some point, I'd like to drop the oil pan, give it a good cleaning, and replace the oil pan gaskets as they are cracked, but not to the point that they are leaking. In the meantime, I'll be increasing the frequency of oil changes as after 2,400 miles, the engine oil was black and smelled burned. I opted for Rotella T1 SAE 30 for the late summer to fall months, a change from the FRAM Conventional 10W-40 I had used last oil change. All cylinders, aside from Cylinder 5 where the head gasket was leaking, had heavy carbon buildup, and I'd imagine there is a good amount of sludge remaining in the areas I could not immediately reach, so I plan on adding Sea Foam or Marvel Mystery Oil to the fuel tank and crankcase. I'll need to find a good coolant flush as the coolant passages within the block are restricted from buildup. I discovered the exhaust manifold gaskets to be missing and have since installed new ones. Being short on time, I didn't have the ability to get the heads checked and cleaned by a machine shop, and even so, I'm not sure it would have been worth investing any more money into this engine as that money would be better spent on a rebuild and swap of another engine. I am, however, interested to see how long I can extend the life of this engine, and depending on the condition of the transmission (leaks from bellhousing and rear seal, harsh engagement), the original drivetrain.


Passenger Cylinder Bank Carbon Buildup & Preliminary Cleaning Results


Cleaned Cylinder Head




Engine Reassembly

Left and right intake manifold gaskets are reversed in this picture, but were corrected before further assembly.

Now that the engine is reassembled and running, I have a new problem that I'm currently trying to resolve:

Symptoms:

1. Vacuum hose going from the large vacuum nipple on the rear passenger side of the intake manifold to the solenoid block has cracked and creates a large vacuum leak that was causing a hard start and backfire condition, however, I have improved this condition by plugging the leak with a golf tee. I will resolve this and prevent future vacuum issues as soon as possible with all new vacuum lines. Hopefully this is the culprit to the overlying issue.
2. Rough idle in park and neutral, much worse in gear.
3. Engine RPM picks up in park/neutral, but loss of power, stumbles and stalls in gear.
4. Hissing from inside throttle body, louder in gear, with throttle input, and on shutdown. (Vacuum leak of some sort?)

Notes:

1. I've seen a number of rough idling issues being caused by the IAC, however, before performing the engine work, the IAC had worked properly and would not explain the hissing from the throttle body.
2. Negative battery cable was removed from battery overnight to reset computer.
3. No leaks from replaced gaskets that I am aware of.
4. No fault codes.

Any help would be much appreciated as this is an urgent matter.

 

Recheck plug wires for firing order. Having one or two off, can cause significant issues.

Did you move the distributor at all while the engine was apart?

Pinched wires anywhere?

What spark plugs did you install?

Does it idle rough immediately on startup? Or will it idle nice for a minute or three, and then start acting bad?

 

Flushing- I have used a method an Aussie told me about. Drain the oil and the old filter. Put the old filter back on. Add half required new oil and a half quart of diesel. Drive normally for a day or two. I usually do at least 50 miles. Then do normal oil change. Supposed to help clean valve seals etc. It is basically the same stuff in that quart of engine flush. I have noticed no problem and it always seems like I drain more than the 2.5 qrts after.
Vacuum leaks will definitely cause symptoms. On the front of the TB the MAP sensor has a rubber elbow that is a vacuum connection to the TB and there is a vacuum line coming up from the passenger side in front of the TB that also connects to the TB on the pass side of the MAP sensor.
Turn the key all the way on for 30 seconds to fully drain the system before you reconnect the battery. A neg cable disconnect for 30 mins is plenty.

 

Replaced the broken vacuum hose from the intake manifold to the solenoid block. Doesn't seem to have made a difference, but the throttle body itself seems to be pulling a strong vacuum now.

Overall, the engine vacuum seems to be greater than before the engine work. I've noticed one of the vacuum nipples on the throttle body pulls a vacuum when before it did not.

I just went out and verified the spark plug wires are in the correct order (1-6-5-4-3-2).

The distributor was never moved.

I inspected the wires, all appear to be good.

I'm still running the old Autolite APP65 Double Platinum spark plugs.

I'll be sure to get new spark plugs.

Immediately on startup. Sometimes while cranking it'll backfire. It seems to get worse with engine load as, if I turn on the A/C or put the truck in gear, the idle becomes low and rough. In gear, throttle input causes the engine to stall. In park or neutral, with throttle input, the hissing continues to get louder with RPM.

Interesting idea, I may have to try this. Thanks for the tip.

I believe the setup you are describing is that of the later Magnum engines. The MAP sensor on my truck is located on the firewall on the passenger side and has a single vacuum line that attaches to the rear of the throttle body.


Thanks for the input, guys.

 

I found a post that describes a similar issue to what I am experiencing.

Considering the head gasket's primary leak was in Cylinder 5, then leaking into neighboring Cylinder 3, and then Cylinder 1, I'd imagine there was a large loss of compression, and now that the head gasket is replaced, along with the heavy carbon buildup, the compression is much higher.

What are your thoughts?

 

Get rid of the platinum plugs. Standard copper plugs from your preferred manufacturer. These engines REALLY dislike the rare-earth fellers.....

 

Thanks for the heads up, I'll make sure to pick up copper replacements.

Any other ideas? The spark plugs may be one thing, but I'm not sure that's the ultimate solution.

 

One thing at a time. If you make too many changes at once, you run the risk of making things worse, and then you don't know which one caused it.

Check and make sure all the ignition parts are in good condition, that you are getting adequate fuel pressure, and you don't have contaminants in the gas.

 

I picked up six Champion RN12YC (P/N: 404) spark plugs the other day. Same as OEM. Advance Auto Parts' and AutoZone's websites claimed to have them in stock at my local stores, but when I went to the stores, no luck. I ordered from O'Reilly Auto Parts and picked them up the next day, but they had made a mistake only ordering three, however, they were able to get the other three by the end of the day, although they charged me twice...

I'll give the Champions a try and maybe give the seemingly favored Autolite 3923s a try next time around.

While replacing the spark plugs yesterday, I noticed that, sure enough, the firing order was off. I had swapped the wires for Cylinders 5 and 3. Oops. Not sure how I missed that!
Good call!

Fair enough.

I can't say the spark plugs were the problem, but they led me to find my own mistake. Either way, as you said, the copper plugs are better suited for these engine anyway.

Thanks for your help!


Now that the truck is running properly, today I removed the thermostat and flushed the cooling system fourteen times until the water came out relatively close to clear. On reinstallation of the thermostat, the thermostat housing wasn't sealing quite right due to corrosion and paint flaking off. Didn't even last a year. Hopefully tomorrow the new housing and gasket will be delivered, I'll finish adding coolant, and the truck will be back on the road.

 

I have done that trick with the plug wires before. Even though I checked it like six times, it was still wrong. Of course, it's not like the distributor is easy to get to.......