Engine install, misfires

[AleroB888]

This is a fresh rebuilt engine with porting of intake and heads, beefed up bottom end but a not too radical cam.

There are pretty severe misfires at lower RPMs, and vibration, but gets considerably smoother higher up in the RPMs. Top end torque is good, much better than stock. The misfires appear real, given the rough running of the engine, but the plugs look perfectly clean when checked. Exhaust is clean. There is only about 200 miles on the engine so far.

In particular, this is a 3400 built-up block, 3500 heads, 3500 LIM, 3400 UIM. '99 timing chain, CR appox. 9.1, Cam is a step up from stock. There is a slight alignment issue with the LA1 fuel rail, and at first I thought that might have been allowing the injector orings to leak at deep vacuum. I replaced the GM 36 lb injectors with RC 35 lb, which fit better as far as proper angle into the LIM, but did not cure the misfires.

I had a local shop install the engine. When it was first fired up, they said it ran about 10 seconds then blew oil out the oil filter gasket. They put another filter on and it happened again. So I told them to replace the oil pump, which I still have. This time it stayed running, but only if the gas pedal was held slightly open. I drove it 3 miles home, but it ran very rough, a lot of vibration. Now, I also had a billet engine mount (the one near the radiator), put on, so some of the vibration may be due to that.

Originally, there was synthetic oil put in, but I drained it out after about 20 minutes of run time, 3 miles of driving, then changed to Autozone brand regular oil. The first oil was darker, but no visible particles. Second oil change at 50 miles, looked perfectly clean.

After some idling and low speed driving, I thought it was starting to smooth out a bit, but the misfires remained. The power/ torque seems to be excellent, it does better cruising when above 2000 RPM.The last 50 miles it's been getting rougher. I want to believe that there is some kind of ignition or electrical issue, but I need to hear all possible theories on it. It idles like an old Harley lol....
I have scan files with HP Tuners that I can link to if necessary.
Thanks in advance.

[SappySE107]

Post the the most recent scan. Idle, and driving if you have it, cruise below and above 2k. Sounds like a vacuum leak or when an EGR gets stuck type of issue.

[AleroB888]

I'll try to attach it here, along with the config. file....


Test-Config-1b.cfg

new engine-test 5-inj.corr.hpl

[Guest]

Verify the plug wire orientation to the correct cylinder. Visually inspect the wires to make sure nothing is cut.

If your injectors are dumping too much fuel it will foul the plugs very quick causing a misfire or a dead cylinder or two. Pull the plugs and see if they are black.

[AleroB888]

The plugs look almost new when checked. I tried regapping from .035 to .060 as well. Also, fuel pressure stays steady, around 50 psi at idle...

[SappySE107]

Other than the fueling on acceleration, it looks fine in the computer. Idle kpa for the MAP sensor is a little higher than stock but the cam is probably the reason for that.

[Nick-G]

I've accidently put my plug wires on the wrong cylinders before and it acted similar to what you're saying.

[AleroB888]

I have now replaced these ignition-related part in the system:

different coils and ignition module,
new plug wires (found one bad wire),
different crank sensor (rear of engine block).

MSD DIS unit has been removed to simplify things.
Upper intake gaskets replaced with thicker ones to make sure manifold clears fuel rails.

I have put a little over 600 miles on it. Oil changes were done again at about 65 and 400 for a total of 3.

During the first 200 miles, a line from the PCV valve got plugged, forcing some vapors out the back valve cover line. But away from the PCV lines, oil seeps down along the edges of the front head gasket and drips from the corners. It has not been nearly as bad since the PCV line was cleared, but there is still some dripping down both edges of the gasket. It appears to happen only when the engine runs, and does not drastically affect the oil level after a couple hundred miles.

So I still have the rough running and the misfires when idling or cruising at low speed below about 1500 RPM. The engine starts well enough cold and continues to run, as long as it can warm up for a few minutes. But backing the car out of the garage just after starting can cause it to die.

When fully hot and on the road it does better at high RPM, if the weather is cold enough. The warmer the weather, say 60 degrees, the more it has trouble maintaining idle at stoplights, or cruising at low speed. When it is fully hot and then shut off and parked for about a half hour, starting is very difficult, even if resorting to opening the throttle.

When the installers pulled the original engine, they said they had to remove the crank pulley. It is possible it got bumped on the first attempt to lift the engine out, possibly knocking it off balance. That and the sensor under it are the only things I can think of that have not been replaced.

I was thinking about putting a stock front trans mount back on, but was afraid the engine itself might move around more, even if less vibrations got to the chassis. As it is, not too comfortable to drive.

[Xnke]

Cam timing or ignition timing is likely wrong.

What exactly are the camshaft specs? Generally you're describing a very retarded cam, or not enough ignition advance at low speed when using a cam with seat durations over about 280*.

This assumes that you've already checked/confirmed plug wiring...a lot of 6-cylinder engines will run in the proper direction if you put the plug wires on in not quite the right order.

EDIT: You "originally" had synthetic engine oil in the engine? As in for break-in???? Big no-no. Can cause serious ring-to-cylinder-wall interface issues. Might wanna check on that.

[AleroB888]

I had told the installers I wanted regular oil put in for economic reasons, since it would soon be changed out, but they put in synthetic anyway, they told me. I did not research break-in oil, since I thought some new model cars came with synthetic from the factory. I changed it to regular oil after about 20 minutes of runtime and a slow 3-mile drive from the shop.

[Blacktree]

[ATTACH=CONFIG]8837[/ATTACH]


I had told the installers I wanted regular oil put in for economic reasons, since it would soon be changed out, but they put in synthetic anyway, they told me.

WHAT?!?!

Any mechanic with more than 2 brain cells knows not to put synthetic oil in a freshly rebuilt engine. Ideally, you should use dino oil with a break-in additive.

Anyway, I'd suggest a compression check, and make sure each cylinder has good spark. Also, what's your oil pressure like?

[Xnke]

Yeah, OEM's use synthetic blends with very specifically designed ring packages and cylinder wall finishes to achieve rapid break-in with minimum wear.

Always, ALWAYS follow your ring manufacturer's recommended break-in procedure. I have never seen or heard of a ring manufacturer out there who recommends anything other than a specific break-in oil, and they are universally a conventional oil, single-weight with low detergent and high levels of extreme pressure lubricants.

So now that we know that, I would check your plug wires, check your plug gaps, and drive the crap out of it for 500 miles and then change the oil and filter.

[AleroB888]

I don't know, putting more miles on it with vibration and misfires going on seems like it would be detrimental.

With the symptom being misfires on all cylinders at RPM below 1800, no smoke out the tailpipe, good high RPM power, I'm guessing the rings are sealing OK. I don't have an oil pressure gauge, but oil looks like it's getting to all areas of the engine, no sensors to indicate a problem there.

What might a compression test indicate? For example, suppose I found that compression was low on all cylinders, what would that indicate? And is it possible for compression to be too high? (I'm not a mechanic, you'll have to keep it simple) I'm guessing the test will have to be done when engine is fully hot, since it struggles to restart when hot. What would low compression when hot indicate? I am expecting results to be uniform for all cylinders. I can do one more scan to see if the misfires are the same on all cylinders.

I can change the oil and recheck the plugs, so far they stayed almost perfectly clean. So I guess I need a guideline for the compression test.

[Xnke]

Low RPM is where bad rings will cause the worst problems-at higher RPM there is less time for leakdown to occur.

To recap, in order:

I'd check plugs and wires and make sure none are fouled or gapped wrong, then i might start checking coil packs. After that, hot compression check.

Pull all the plugs out, check each cylinder 1 at a time with the throttle blocked open 100%, unplug the injector harness so no fuel is being injected.

Low compression on all cylinders doesn't mean anything, persay, as long as all the cylinders are within 3-5%

If it is struggling to restart when it's hot, chances are it's a fueling problem. Check your coolant temperature sensor for the computer, as if it's wrong or miswired it will swing the fueling calculations WAY out.

Check for fuel injectors not firing. One injector missing will be an issue at low RPM, but at higher RPM where the open times overlap you'll just start pulling fuel from the plenum and that cylinder will fire-will be lean, but firing.

[AleroB888]

Before I go further, is this a normal condition for the hub of the crank pulley to have a gap there?
It's like that on every picture I can find of it.