The Jasper Engine

[BodybyFisher]

Jim, I am curious what you think, I see a difference between those two plugs. Look at the center electrode, #8 looks overheated whereas the other plug is grey. What does that indicate? There is definately a difference between these two plugs, its probably due to a rich mixture, see this

Powdery black deposits on the plugs can occur from "carbon fouling." The underlying cause here is a rich fuel mixture.

from this article

http://www.aa1car.com/library/sprkplg2.htm

[Cadillac Jim]

Background: These plugs have about 10,000 miles on them. The engine has about 45,000 miles on it. The engine developed low compression on number 8, about 80 psi tested cold, cranking speed, with the throttle open, and the PCM started detecting a miss, eventually turning on the MIL when the miss count exceeded some threshold. The miss is most apparent as a hard miss when idling cold with the temperature below 40 F. An unevenness at idle is apparent when idling in gear, even hot, that the PCM detects and makes the P0300 CURRENT and increments the miss counter, but I don't believe that it is a "hard" miss but simply a weak cylinder. Under even light thottle and RPM over 1,000, the miss goes away and the engine runs smoothly and normally, with no discernible performance problem or fuel economy problem.

There are differences in construction of the two plugs too, like they are from different suppliers or at least different production runs. This is most obvious in the length of the center electrode, and the difference in the platinum tip. One looks like it was contact-welded on, the other looks like it was sintered on. The ground electrode is also thicker on the "other" plug than on the plug for number 8, something that you can easily see even though the magnification is slightly higher for the "other' plug.

The difference in the insulator is obvious too. The "other" plug is white, almost like a new spark plug, while the number 8 plug is brownish. Both are in the normal range. The engine has had several hours of testing and running at idle with a miss on number 8, which accounts for the look on its insulator.

Overheating of a plug will leave a whitish deposit on the insulator and electrodes and I don't see that. In any case it's just about impossible to have a condition like that on a Northstar without a code for a lean mixture. This car has never had codes for lean or rich mixture, ever.

I believe that the main difference of note is the brownish insulator on the plug for number 8. This is accounted for by the fact that the last several days or weeks of running were with low compression on number 8. The compression was blowing back into the intake, reducing the charge on the next intake. The closed loop operation will keep the mixture within limits but what it was is speculative. What we know for sure is that it was within the limits of the fuel injector because we didn't get a code.

As far as abnormalities, I don't see any. The ground terminal looks much the same for both plugs, albeit the one for the "other" plug is a bit thicker. The center terminal has a shorter sparking projection on the plug for number 8 and the platinum tip has a different appearance but I don't think it was because the engine was melting platinum (melts at 2042K or 3708F; aluminum melts at 933.5K or 1712 F).

At the end of the day, I don't think that the plugs tell us anything we didn't already know, nor did we expect them to. All we know for sure is that there is a compression leak into the intake (you have the invoice where the tech wrote "through intake valve" on the notes for the bleeddown test; he told me that it was a loud hiss). We won't know more until we pull the head, and even then the leak may not be visible.

Until we have the intake valves out and can look at the intake valve seats and the sealing surfaces of the intake valves, we won't know absolutely for sure that it was a valve or which one. Even then we may not know why. You sent me a link on an excellent article that said that most valve failures were heat-related, which is vanishingly rare on intake valves, but that 20% of valve failures were due to metallurgical flaws in the valves themselves. Up to now we have eliminated, or have no reason to believe, any of the known causes of valve failure. We won't be able to even think about metallurgical failure in the valve itself until we see it, probably out of the head.

We can hope, though. A metallurgical valve failure could manifest itself as a chip in the edge or a radial crack. Again, we won't know until we get the head off.

[Cadillac Jim]

Jim, I am curious what you think, I see a difference between those two plugs. Look at the center electrode, #8 looks overheated whereas the other plug is grey. What does that indicate? There is definately a difference between these two plugs, its probably due to a rich mixture, see this

Powdery black deposits on the plugs can occur from "carbon fouling." The underlying cause here is a rich fuel mixture.

from this article

http://www.aa1car.co...ry/sprkplg2.htm

The plug isn't fouled. The tiny specs on the insulator are not visible to the naked eye. This is a microscope's view of the plug. You are seeing things here that you never saw on a plug before, such as the fact that the plugs are clearly of different manufacturing processes. Even more is visible on a glossy print because the file is cut down for the web. The insulator is a bit dark because the compression is about half what it is supposed to be and the cylinder has a miss at cold idle. The compression leak is to the intake. That causes the mixture to be irregular and difficult to manage and probably variable. There is nothing here that is not expected of a cylinder with low compression and a miss.

[BodybyFisher]

thanks

[Cadillac Jim]

#PIP3146D: Rough Idle Crank No Start Extended Crank Or Misfire When Cold Due To Sticking Valves Or Excessive Carbon On Top Of The Valves - (May 11, 2011)

Subject: Rough Idle Crank No Start Extended Crank Or Misfire When Cold Due To Sticking Valves or excessive carbon on top of the valves

Models: 2000-2012 All Passenger Cars with Gasoline Engines

2000-2012 All Light Duty Trucks with Gasoline Engines

This PI was superseded to update recommended field, model years and engine list. Please discard PIP3146C.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

Rough idle, misfires, extended crank, or crank no start when cold. The engine may run rough for up to 5 minutes after starting the engine and may exhibit a P0300 DTC too. This may be caused by sticking valves or excess carbon due to fuel contamination

Note: fuel oxidation and volatility concerns can often cause these issues as well, however they cannot generally be checked in service. Trying a different, high quality fuel is sometimes the best diagnostic.

When the engine is cold, the compression on multiple cylinders may be at 0 PSI. The engine also may pop through the intake or exhaust while cranking and the spark plugs may be fuel fouled when inspected. Some engines may also experience valve damage or cam followers that are out of position as a result of this.

This condition can occur in specific areas of the country for a period of time and then it will no longer occur after the suspect fuel source has been consumed in that area of the country.

Recommendation/Instructions:

If the SI Diagnosis leads to a compression loss due to sticking valves, the following information may help:

If there is no sign of valve damage or cam followers that are out of place, perform the following procedure to free up sticking valves and to prevent the valves from sticking again. If valve damage is present or if there are cam followers that are out of place, perform engine mechanical repairs as necessary to correct the concern and then perform the procedure below to prevent the valves from sticking again.

1. Clean the fuel system by following the applicable "Fuel System Cleaning" procedure outlined in SI.
2. Add fuel injector cleaner "GM Fuel System Treatment PLUS, P/N 88861011 (for U.S. ACDelco, use 88861013) (in Canada, 88861012)"... see This PI was superseded to update recommended field, model years and engine list. Please discard PIP3146C. bulletin # 05-00-89-078B, to the fuel tank in the approved quantities.
3. Refill the fuel tank using fuel from a high volume, high quality filling station.
4. Clean the induction system using GM Top Engine Cleaner. Follow the directions on the can but DO NOT force the engine to stall since forcing the engine to stall with liquid Top Engine Cleaner could cause the engine to hydro-lock. * If available use an atomizer with Top Engine Cleaner through the throttle body.
5. Advise the customer to change fuel filling stations. They should use fuel from only high volume, high quality filling stations or they should use a Top Tier Detergent Gasoline if available. See 04-06-04-047I (U.S.) or 05-06-04-022G (Canada) for details regarding Top Tier Detergent Gasolines.

ADDITIONAL SI KEYWORDS:

None

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a ""do-it-yourselfer"". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information. WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

© 2013 General Motors. All rights reserved.

[Cadillac Jim]

Here is the invoice for the compression test and leakdown test that I had done on March 6, 2013. This is the last of testing and work that I had done over about a week that began with new coils, wires, plugs, and restoration of plug wire looms and conduits to factory original condition. A miss at idle was still present as verified by an engine analyzer seeing the miss count for number 8 still increasing. A compression test at that time showed 160-180 psi in all cylinders except number 8, which was 75 psi that day. Here, about a week later, are the results of wet/dry compression testing and a leakdown test. I talked to the tech that did the work on March 19 when I got back to town with the CTS-V and he told me that they used a make with a three-letter name that I don't recall. His description of its operation is that it has two gauges, a fitting for the spark plug hole, and a fitting for shop air at about 100 psi. The cylinder is put at TDC firing and shop air is applied. One gauge reads pressure and the other reads flow. A table that comes with the instrument provides the leakdown percentage figure. This is consistent with the OTC Leakdown tester, offered on Amazon.com here. The tester used is this one or an equivalent tester of another make with a three-letter acronym. I can verify the make with a phone call if anyone thinks it's important.

The particulars of the shop and my contact details are blacked out because this is a public forum. Anyone who wants to see the whole invoice, please send me a PM.

The top page of the invoice:

Here is Page 2.

Here is page 3, the handwritten notes taken during the test.

[Cadillac Jim]

There has been a lot of discussion about the wet/dry compression readings. In particular, number 8 read 80/130 psi dry/wet and many took this to mean that there was a problem with the rings on number 8. The head has been off since, and the cylinder bore on number 8 shows the same cross-hatch pattern as the other cylinders on the front bank, so the dragon of a cylinder bore worn slick does not live here. The cross-hatch on a modern engine holds the oil that lubricates the compression rings, and a slick bore will run the compression rings and cause loss of compression in the cylinder. But that didn't happen here.

The key is the readings on number six, 180/285 psi. The compression specification for this engine is 140 psi to 170 psi, according to the 1997 FSM page 6-11. A compression reading of 285 psi wet doesn't mean that there is a problem with the rings and that all the cylinders should read 285 psi, of course. But with a compression ratio of 10.3:1 and a total piston displacement of 4564.83 cc (278.56 cid), the combustion chambers are 61.36 cc including the head gasket. A tablespoon of oil is about 15 cc, so two tablespoons of oil (too much!!!) would account for the wet reading of 285 psi. This would also account for the reading of 130 psi on number 8, still below the minimum specification of 140 psi dry. In any case a leakdown test was done that determined that there was no significant leakage into the crankcase or exhaust on number 8, and no significant leakage on number six. Number 4 was also tested but it had the same numbers for all tests as number six so it wasn't put on the invoice, since these numbers were only a reference for the numbers for cylinder 8.

[Cadillac Jim]

Once the head was off on April 22, inspection revealed a string of goop around one of the intake valves on number 8, including wrapping around and including some on the sealing surface between the valve and the valve seat. This accounts for the compression problem. The head rebuild was completed by the machine shop on April 26, 2013.

Another problem surfaced on April 24. BodybyFisher noticed that the timing chain tensioner on the back bank had lost its Teflon shield on the shoe and that the timing chain had cut into the aluminum by a considerable amount. Inspection revealed that the non-rotating lifers had no discernible wear on the portion not wiped by the cam lobe, indicating that the lifter had never rotated since the engine was put together.

The combination infers that when the engine was first started, the Teflon on the rear (upper right) timing chain tensioner shoe detached or broke up and the cam chain started wearing into the aluminum of the shoe. The relatively large debris could have gotten through the oil filter bypass before the engine warmed up and gotten into the lifter gallery where it managed to prevent two or thee lifers from rotating.

[Cadillac Jim]

One of the lifter bores on number 8 is demonstrably looser than the others. The head was sent back to the machine shop to have it checked to determine whether it was within its maximum tolerance of 0.003 inches. At this time, May 23, 2013, we have not heard back.

There was speculation that this large clearance allowed oil pressure loss that would collapse the lifter and cause the miss. This is doubtful at best because the car did not have a performance, economy, or any other problem except for a barely perceptible miss at idle, and it did not have a lifter noise of any kind, much less a dry lifter clatter. In spite of the fact that the miss and compression problem had been diagnosed on March 6 as an intake valve leaking, this became an object of discussion and decision in matters such as scrapping the rebuilt head. In order to look at this, I estimated that most oil shed by the lifter would be the oil left behind as the lifter moved.

A valve lifter moves by the amount of the valve lift twice each time the cam lobe lifts it, and that is once every two revolutions. The lifters are 33 mm in diameter. Assuming that all the 32 valves have 0.003 inches clearance on the lifter bores all around, for 0.006 inches total (twice the allowable limit) and all the valves have the VIN 9 intake valve lift of 9.4 mm (the exhaust valves have 8.6 mm lift), that would be 26 cc per second at 650 rpm, and 277 cc per second at 7000 rpm, a small fraction of the oil capacity of a high performance engine like the Northstar. The pressure head of oil for, say, two feet from the oil pressure switch to the lifter gallery would be about 0.7 psi. So it doesn't seem reasonable that lifter bore clearance could cause a problem with oil pressure.

[Cadillac Jim]

Anyone with news or information on completing the valve job and cam tensioner replacements for the Japser engine is welcome to post that information here.