1992 Infinity Q45 6/91 Production date with single very weak cylinder

[Frank's Generator]

Hello All, I have a 92 Infinity Q45 with 100,000 miles on it that has just had 8 new injectors installed for the reasons that 2 were open circuit as measured at each injector with the remainder being replaced due to difficulty in ease of replacement in the future. All the cylinder pressure tests were performed and each cylinder has @160 psi cranking throttle closed. Each independant ignition coil is creating the nominal output energy to fire the plugs, so no question of a failed coil or igniter assembly / wiring harness. 8 New platinum NGK plugs are in the engine and gapped appropriately. The problem is that one cylinder (#6) is creating about 5% of the horsepower it should. After reverifying cylinder pressure, spark plug quality and coil operation as well as igniter I am at wits end.The possibility of an air leak in that particular cylinder was addressed by spraying carb cleaner around ALL potential air leak areas such as lower manifold to cylinder head, lower manifold to upper plenum and finally the base area of the injector. If there is a gasket leak it is not drawing outside air but possibly crankcase? Is that at all possible in this engine / manifold design? Could there be a heavy build up of carbon on the rear of this particular cylinders intake valve as in the BMW / Benz / Caddy engines of yesteryear??? Why a single cylinder? Each of the other cylinders when either the fuel or spark is removed creates a true RPM drop easily noticed.#6 when either fuel or spark is removed there is a VERY slight RPM drop and furtherence of a missfire. What say the assembled masses as I do not relish disassembling this engine to physically see if I am beseiged with carboned up valve seats?

[DAEDALUS]

2 possibilities come to mind: Problem with the new injector or perhaps one or more valves are at least partially stuck closed. Try performing a vacuum check. If the needle remains steady, suspect the injector. If not, suspect a valve-train problem. Depending on how much is invested in tools and equipment, there may be ways to confirm the problem without a complete teardown.

[DougQ45]

I also suspect an injector. Perhaps the nozzle was bumped when installed and now it will not atomize fuel well?? I had that happen on my 1990. Consult indicated lean miss at idle on #2 cylinder. When I pulled the injector, it ohmed fine and was working but sure enough, the tip was cracked badly. A shot in the dark, but makes more sense than your engine components going south with only 100,000 on the motor. Good luck.

[Frank's Generator]

Good Morning All,

As of last week I also thought the injector was the issue. I removed the suspect injector and had it checked by a rebuilder on a test bench.

The injector was fine although I was not there to see it atomize the fuel myself.

When I pulled the plug on some previous tests the plug was wet with fuel.

To verify I did not have a borderline plug or coil issue I moved the coil to another known good cylionder and replaced the plug with a brand new one.

If it is in fact not a mechanical engine problem and not an injector what else could it be other than carbon in the valve area?

How many times have you seen yourself or heard of a similar problem in an infinity / nissan engine and have it not be the injector?

Would you not suspect each of the cylinders intake valves would be similarly compromised if in fact #6 in my case is possibly loaded sufficiently to cause this problem?

I suppose a fuel pressure drop test on each injector to verify fuel usage and possibly a peak into the cylinder with the suspect intake valve open in hopes of seeing atomization in the cylinder while manually firing the injector is worth a shot.

Frank

[DAEDALUS]

What does the vacuum gauge say?

[Frank's Generator]

Hello All,After going through the complete diagnosis and performing the injector pressure and volume tests I have ascertained the injector is in fact at fault.

Additionally with sufficient light I was able to peer down inside the injector ports and see the rear of the valve chambers which were void of carbon deposits.

I am purchasing a new injector unit from Infinity today and am awaiting the response from the original remanufacturer of the 8 injectors.

I am sure the one injector either has incorect internal components in the nozzle / pintle or plain was not remanufactured identical to the other 7 which are 100% and have the same pressure and volume drop numbers.

Stay tuned as depending on the rebuilders reply to my E mail describing the problems they caused me, I will decide within the next ten days if I can cautiously recommend this particular rebuilder or slam them here but good.

I would have never thought to purchase remanufactured injectors for a gas engine if it was not for the infinity new price / reman. differential and the assurance the rebuilder had been in the business for many decades and warranteed their product fully.

Thanks for the sounding board from two guys that obviously have been around the block.

[Q45tech]

Please spell Infiniti correctly.

Over the years we have never found any so called injector rebuilder worth using........most just clean up old very used junk yard units and resell the ones that seem to work.

Very very dangerous to assume rebuilt injectors are anywhere like brand new ones!

We see lots of damage from using them!