Help me diagnose my motor? (non-firing cylinders)

[Chillin014]

I recently purchased a low mileage j30 that needed some work. When I first started the car it had some noises, primarily what sounds like the idler pulley (very scratchy). I can provide a video but it doesn't pertain to the major problem at hand.

The motor runs kind of rough, and I've narrowed it down to cylinders 5 and 6 (the rear most cylinders). I unplug the coils one at a time and notice the motor stumble except on the 5 and 6 coils. So I swapped the coil on one side to check if the coil was bad but the behavior did not change. I decided to do a compression check and all cylinders checked out fine (170-180 psi). Nothing alarming when I pulled the spark plugs. While cranking the motor for the comp. check I noticed fuel spraying out of the cylinder 5 spark plug hole (i forgot to depressurize the system). So that tells me its getting fuel. But maybe not spark?

does this sound like anything familiar? Everything firing except the rear most cylinders? Otherwise the motor seems very smooth.

I appreciate any help.

I also thought i'd mention that this is a 94 which I read is not obd-2 unfortunately.
Modified by Chillin014 at 11:43 PM 5/23/2009

[GerryO]

Use a multimeter to ohm check the injectors at about 11.5 ohms. Probably a failed/open injector coil (infinite resistance). Replace with a new OEM injector, not remanufactured, along with new upper and lower o-rings.

[Chillin014]

I will definitely check that out, although I thought I saw gas spraying out of one of the cylinders during the compression test. Anyway. I'm going to replace the spark plugs, put it all back together and test the injectors.

I'll report back in a week with results when I get back to the car.

[patterned]

It's possible your injectors are running wide open.. soaking your sparkers and not allowing for combustion. i'm guessing you are seeing bad fuel mileage, and a severe stumble from running on 4 cylinders. pull your spark plugs and check their condition.. wet, rich, excess carbon?

here is a reference:http://www.dansmc.com/Spark_Pl....html

Otherwise, do as suggested and ohm them out. Replace as needed.

[Chillin014]

Ahh, I can see that. I actually haven't driven the car, I've only owned it for a week, and bought it to fix-up. It definitely runs crappy though, after it warms up it idles so hard it visibly shakes the whole car.

The plugs looked about average. The two rear ones seems a little darker than the rest but nothing jumped out at me. I'll have to check again when I get home. Does obd-1 not throw a code for things like injectors and coils?

thanks

[patterned]

Just recently, I've had both 5 and 6 go out on me, as well.It ended up being fuel injectors.. bought some reman's from rockauto for about 45$ a pop, and it runs just fine..If you have spark, and compression (grab a tester for 20$ at sears), then your problem is fuel.

I've heard it mumbled that injectors like to go out in pairs.. or to replace them in pairs.. Don't know why, but it did happen to me.

Run a compression test if you're worried about wasting money (I am) to double check it's your injectors.Take your plug wires off and test them against an engine bolt to make sure you are getting a good, solid, consistent spark... You said you already switched the coils, so your spark should be fine. Just make sure your plug wires aren't cracked, limiting voltage.Also check your distributor cap/rotor. Cheap, easy fix if you've got cracked leads in the cap.

[Chillin014]

very cool. thank you for the response. I will most likely get the reman'd injectors as well if that turns out to be the problem. Rockauto ftw.

I already ran a compression test and everything turned up fine. I will check that distributor as well.

[GerryO]

I will check that distributor as well.

There's no diz to check.

[Chillin014]

my mistake. I was calling the "camshaft synchronizer" the distributor but obviously there is no cap and rotor there, it looks like just an electrical piece.

[Chillin014]

Alright I finally have had some time to work on it. I bought new spark plugs (NGK Coppers). It looked like the original factory platinums were in there. (The car has 100k on it.)

So anyway, I installed the new plugs and 2 junkyard coilpacks on the rear cylinders which I suspect to not be firing. There was no difference in how the car ran. I didnt check the coil packs or anything but I have a hard time believing they were both bad so I'm going to move on to the next suspect which I fear is the injectors. I really didnt want to have to remove the intake manifold

[Chillin014]

Alright I tried to "stethoscope" with a screwdriver to each injector and they were all clicking away. So I got my ohm-meter on there and got some results. On the driver side bank everything checked out as suspected. 11.3 ohms on all except the rearmost cylinder which read "OL" until I increased the ohm setting to the 200k setting and started getting a reading. Now to the passenger bank which was the opposite. Here they were all giving me way above spec readings EXCEPT the rearmost cylinder which read 11.3 ohms.

I also noticed that when I unplugged the rearmost pass. cylinder the engine stumbled and died at idle. It never did this before...so I dont know if the new coilpack/spark plug made a difference in that cylinder but the motor still runs equally crappy.

Despite the readings given by the injectors I still don't feel real confident that they are the problem. Cylinders 1 & 3 read high yet I know those cylinders are firing relatively normal.

[Chillin014]

I just did the OBD1 diagnostic light festival and came back with "2 1" as the only code. That is something to do with the ignition but what exactly I do not know. I want to say the only reason that code is there is because I was unplugging coilpacks while the car was running.

[Chillin014]

Okay I realize nobody is interested in this anymore but for reference purposes I will continue to post progress.

I was messing with the car again today and I've definitely got 2 cylinders not firing. Originally I thought it was both rear cylinders but it actually seems like its the middle cylinder on the passenger side rather than the rear. If I pull up the coils on these non-firing cylinders I can hear the spark jumping between the coil and the spark plug so I can pretty much rule that out.

I am on a pretty strict budget so I'm going to try to get my hands on some working used injectors. This HAS to be it. No sensor would effect the motor in this way right? Especially if the ignition is working properly.

[GerryO]

Alright I tried to "stethoscope" with a screwdriver to each injector and they were all clicking away. So I got my ohm-meter on there and got some results. On the driver side bank everything checked out as suspected. 11.3 ohms on all except the rearmost cylinder which read "OL" until I increased the ohm setting to the 200k setting and started getting a reading. Now to the passenger bank which was the opposite. Here they were all giving me way above spec readings EXCEPT the rearmost cylinder which read 11.3 ohms.

I also noticed that when I unplugged the rearmost pass. cylinder the engine stumbled and died at idle. It never did this before...so I dont know if the new coilpack/spark plug made a difference in that cylinder but the motor still runs equally crappy.

Despite the readings given by the injectors I still don't feel real confident that they are the problem. Cylinders 1 & 3 read high yet I know those cylinders are firing relatively normal.

I apologize for so much in review.

Disconnecting and reconnecting coil pack wires is the surest way to determine which cylinders are bad, the idle will drop when you disconnect a working cylinder and increase a bit when you reconnect it.

Disconnecting and reconnecting coil pack wires on non-operating cylinders will not change the idle speed at all.

Once you have identified which cylinders are a problem, swapping coil packs will indicate if you are lucky, having only a coil pack problem.

The screwdriver stethoscope listening method can be very misleading, but the ohm check is definite. The higher the resistance (all the way to infinite), the more difficult or impossible it is for the individual injector coils to open and close the individual injectors. As I recall the maximum resistance reading is 14.0 ohms. An electrically bad injector should trigger a CEL and register a code.

A noid lamp plugged into the harness connections will tell you if there is power to the injector.

Injectors can clog too, but I believe it's more common for their coils to fail.Factory platinum plugs are reportedly the only plug to run in the J30.

A lot of people have used the dremel method to remove/replace injectors without removing the plenum, but first you want to be absolutely sure which ones are bad. Installing new upper and lower o-rings is essential too, to prevent fuel leaks and possible fire.

De-pressurize the fuel system by pulling the fuel pump fuse while the engine is running (leave it out until you have completed the repairs), remove the fuel cap so that pressure doesn't build back up due to heat, and temporarily plug any disconnected fuel lines.

My first injector failed (infinite coil resistance/open circuit) at about 170K miles. It worked intermittently for a short while, before it failed completely.
Modified by GerryO at 12:46 PM 6/9/2009

[Chillin014]

Thanks for the reply. I understand the whole diagnostic coil procedure. I think its pretty clear that its an injector problem I'm dealing with here if they are that common to fail. This car only has 100k on it though but...if it was a common problem then I guess its no surprise.

Thanks for the confirmation on the injector readings. There were definitely 3 that were reading very very high and 3 that were perfectly in spec. I didnt have any codes in the ECU for injectors ..I dont know how OBD1 responds to something like that. But anyway, you are saying that the higher the resistance just means the injector is faulty? Not necessarily open or closed but just unpredictable performance?

I will check the power to the injectors as well just for the hell of it. I've got a full set of used injectors here locally I think I'm going to jump on since they are only 70 bucks.

I havent decided if I'm going to pull the plenum yet or not to replace them.

As far as the plugs go...I'll leave the new ones I bought in there for now and swap the old platinums back in if I need to later.

Also, I think the power steering pump is going back (its what makes the scratchy noise) AND the water pump leaks. What is wrong with this motor!!

[GerryO]

Thanks for the reply. I understand the whole diagnostic coil procedure. I think its pretty clear that its an injector problem I'm dealing with here if they are that common to fail. This car only has 100k on it though but...if it was a common problem then I guess its no surprise.

Thanks for the confirmation on the injector readings. There were definitely 3 that were reading very very high and 3 that were perfectly in spec. I didnt have any codes in the ECU for injectors ..I dont know how OBD1 responds to something like that. But anyway, you are saying that the higher the resistance just means the injector is faulty? Not necessarily open or closed but just unpredictable performance?

I will check the power to the injectors as well just for the hell of it. I've got a full set of used injectors here locally I think I'm going to jump on since they are only 70 bucks.

I havent decided if I'm going to pull the plenum yet or not to replace them.

Also, I think the power steering pump is going back (its what makes the scratchy noise) AND the water pump leaks. What is wrong with this motor!!

Ohm check those used injectors before you buy and consider that age is probably a factor too. You can look up the code for a failed injector elsewhere on this site (Code 51). The forum that you've posted in probably doesn't get nearly as much activity as some others. The engine is very much the same as is used in the 1990-96 300ZX.

The leaky water pump may be a sign that it's time to replace the timing belt, as typically the two are replaced at the same time and the VG30DE is an interference engine, so if the belt fails, things get bent.

Preventive/scheduled maintenance is the key and the previous owner(s) may have just let things go. If you can do the work yourself, it's a good car and the repairs aren't too bad.
Modified by GerryO at 8:35 PM 6/9/2009

[Chillin014]

alright, its been awhile since I've updated. I bought 3 used injectors which all ohm perfectly within spec. So I began the procedure to remove the intake manifold and all I can say is wow....what a PAIN IN THE a**. I have never seen such an intricate cluster of vacuum hoses in my life. And they are all hard to get to as well. Anyway, I've got it off and have no come to realize that another injector is out of spec....reading way too high. So now I am waiting on getting another one while trying to source all the gaskets I'm going to need to put this mess back together. I hope these injectors solve the problem.

[GerryO]

Take it slow, making sure that you don't end up with any coolant, fuel or vacuum related leaks and that all of your electrical connections are correct/good. You might also want to replace all of the upper and lower injector o-rings, both PCV valves and there are so many things that can be cleaned (EGR tubes, throttle bodies, plenum, IAC/AAC valves, etc) while you have things apart. Hope those used injectors have fewer miles on them than the ones that you are replacing.

[Chillin014]

I know, I am. The injectors "ohm" in spec so I am crossing my fingers.

the EGR tubes were COMPLETELY clogged but I don't think I can thoroughly clean them without removing them from the car and I havent even looked hard enough to see where they connect at the back of the motor.

[GerryO]

Here's a photo of where and how the EGR tubes connect to the EGR valve. Four 10mm bolts to the EGR valve, two gaskets and a few mounting brackets.



They are A LOT easier to remove than the EGR valve itself and can hold surprising amount of carbonized crud.

Best of luck.

[Chillin014]

haha my god those are long tubes! Thanks for the picture! That is the worst area to get to...what a messy motor. I will see what I can do/feel like doing.

[Chillin014]

okay I replaced all the injectors that gave me a bad readings, sealed everything up and reinstalled the intake manifold, etc. First of all let me just say...wow what a JOB. I have never worked on a car with such intricate vacuum and coolant lines and such ridiculous routing. Now I understand why people complain about working on their 300zx's...

ANYWAYS. The car seemed to run a little better...it is more responsive when I rev it up. However...it still has a bit of a rough idle and I think there is a misfire. I didn't even bother driving it as there is this coolant leak which I can not find the source of (it was there before I did this "overhaul"). It leaks down on to the header on the driver side and then burns up. Could this be a headgasket? The car doesn't overheat.

I give up...I'm going to sell the car as it is.

[mtcookson]

Its certainly possible that the head gasket could be bad due to where its leaking though it could also be leaking on to the head then go down to the manifold. Hard to say without inspecting the area real well.

Might try a compression test just to see if that might be the case. That would definitely cause running issues if it were a bad head gasket.

[Chillin014]

thats kind of what I was thinking too...except I already did a compression test and it came out perfectly fine. I'm going to inspect it more but I'm already listing the car for sale...the idea of taking off the intake manifold and then digging deeper into the motor is real unappealing.

[GerryO]

The coolant leak could easily be one of the many under plenum throttle body heating hose connections.

Before:

After:

But possibly not recommended for areas with very cold winters, and I removed one too many pieces of tubing (the AAC valve heating one) that shouldn't be too difficult to replace.

Keep us in the loop, and I can provide more photos and info.

[Chillin014]

haha, I live in Houston, and trust me...I would bypass those stupid lines without a second thought if I was keeping the car for myself. But honestly I only bought the car to fix and sell and didn't want to bother modifying anything. I did make sure to connect those lines properly though as I did see their purpose and significance but I'm fairly sure they are not the root of the problem. I wish it was though. I will try to inspect it a little better at my next opportunity. The reason I thought it was coming from somewhere else is mainly because the leak was there before I even started taking things apart.

I would turn the car off and a large puddle would accumulate under the car over a day or two...half a quart at most.

[GerryO]

Water pump or heater related coolant by-pass lines running beneath the lower intake?

[HowlerMonkey]

Man...........this pic gives me a horrible flashback to having to replace those egr valves under warranty on the Z32 at the dealership.

I think I still have dents in my head from balancing the exhaust system on it as I struggled to get a couple of bolts in to hold it up.

Still better than performing a "van recall", back in 1993, though.

[Chillin014]

haha I've had my share of EGR problems, there seems to be enough room in the j30 bay to access it OKAY, but on my Maxima it was wedged way down in a crevice in hell.

Anyway...I think the motor is running normal now actually. I drove the car some more today and it actually has a bit of pep! It drives very soft and isn't extremely responsive but I think it will make a decent daily driver for somebody. The injectors actually did the trick! yay!