Another Fuel Inj Bites the Dust?

[McShanks]

I replaced 2 fuel injectors (#3 and #5) over a week ago using the Dremel method so I would not have to mess around with the intake plenum. Over the past 2 days, I have noticed that at idle, there seems to be some intermittent miss. A randomly-timed putt-putt. Balance Test revealed nothing. So Yesterday, it seemed worse. I held the throttle at 2000 RPM. A couple times a minute it would seem to miss and RPM would dip a little bit.. When I held it at 3000 RPM, it would run smooth for about 3 seconds or so, then dip dramatically to around 2300 RPM, run rough for about 3 seconds, then roar back up to 3000 RPM, and the cycle continues. Did it at 4000 RPM, and the same thing, dipped to about 3500 RPM, same cycle. And when I let off the throttle, the engine was VERY rough as the RPM dropped back to idle. I can't seem to find anything on this type of issue, don't even know what it's called. It's not really hesitation, because the car responds fine when I push the throttle... And the problem is more pronounced in the mid range. Before, when I had 2 bad injectors, the car was VERY rough at idle, the whole thing would shake. Now, it is very smooth and quiet, doesn't shake, even when I hear the missing. I checked all my electrical connections and vacuum hose connections, and I don't hear any hissing. All brand new NGK PFR6-11G spark plugs. Any suggestions? Links to similar threads? I am gonna do ECU diagnostics today. It wouldn't surprise me if the #1 injector is going since the other 2 in that bank were bad.

[BigTDogg (MA)]

So any codes?

Could be an unrelated MAF issue as well.

[Chase300]

did you gap your plugs properly? and if they are preset did you check them to make sure?

[McShanks]

Sorry it took me so long. I finished working in INdy last week and am transitioning back to Lafayette/Purdue. Finally got around to this today. ECU codes: BOTH right and left Exhaust Gas Sensor Circuits are coding (33 and 53). So, something with the O2 sensors. Getting a drink, then checking O2 ECU diagnostic (heated mode.) Any idea what can cause this?

The O2 Sensor is open or shorted (abnormally high or low voltage is registered).

Harness and connector
O2 sensor
Fuel pressure
Injectors
Intake air leaks

Help... Both are coding. So unless both O2 sensors went bad, I am thinking it is something else, but where to start???

[McShanks]

And, I guess the Check Engine Light is supposed to be on with these codes in, but it is not. Any ideas? Checking Each O2 heated sensor mode now. BRB.

[McShanks]

Ok, so here it is: at 2000 RPM both left and right are normal. When I bring it up to 3000 RPM, the left one is lean the whole time. At 3000, the right one operates ok for a few seconds, then goes lean and the engine stumbles as stated above. I don't hear any vacuum leaks. I am assuming injectors are working ok, since at 2000 both sides are balancing properly between lean and rich. (Light blinks on and off steadily) If it was the sensor or harness/connector itself, I would be getting nothing on the O2 tests. So either it IS a vacuum leak, or there is something wrong with my fuel pressure. Any help would be much appreciated.

[McShanks]

Ok, so a little non-Z related research suggests that perhaps what I am hearing at idle and especially at barely-open throttle is detonation. Almost sounds like popcorn making that putt-putt noise, which is one of the descriptions of detonation. I am going to get a timing light and check the timing this weekend. My CAS is not close to center (the bolts are not near the center of the slots) so I am wondering if the PO attempted to "adjust" timing to correct the lag due to the 2 dead injectors. At high RPM, I have no issue. with WOT on the road, no issue. Am I on the right track? Acceleration seems smooth and powerful enough, but it is low throttle that I am experiencing this dip in RPM and power. At least it doesn't seem like pre-ignition. The CAS is adjusted about 1/4th to 1/3rd of the slot length counter-clockwise when looking at it. Looking here: http://www.twinturbo.net/nissan/300zx/f ... ensor.html It seems like someone "retarded" the timing some? This could cause detonation. What does pre-ignition sound like? Any other ideas? The more the merrier!

[McShanks]

Bump

[McShanks]

bump

[fabbio25]

Having this same problem with my 90tt. The engine runs smoothe until cruising around 3-4rpm's. Then i get almost like a bogging/slugish felling in the throttle. Thought it may have been a bad spark plug but not sure. Im not gonna mess with it unless it gets worse. Other then that the car is running great.

[McShanks]

Yeah, that's similar to mine. Lightly open throttle is when it will not hold steady. At higher RPM, it is fine. I checked my Timing, it is at about 14* BTDC, which is fine. needs to be 15+-2 I think. So, my next step is to take out and check/clean the IACV. I guess the AAC can cause this exact issue. Anyone have input on this?

[Ace2cool]

Have you guys done the carbon canister delete? If so, there is a line on the bottom of the DS throttle body, facing forward, that people almost always forget to cap off. It will cause issues exactly as you are describing. There's also a line similarly located on the passenger side throttle body, facing toward the passenger fender, that will cause light throttle input problems as well.

[McShanks]

I don't believe that is the case with me. I am thinking it is mt iacv, and I am going to get a used one for about $40 and see if that works. I feel like I am kinda pissing into the wind here, but not sure where else to go. It is a small minor issue, but kind of annoying. I am trying to determine whether or not it would be worth taking to a mechanic just to diagnose... ~ $70 or so for that.

[TTkickedin]

I believe the 5.3 vortec should be coming sooner!

Seriously though, I wouldn't be suprised if the other injectors were bad from the start of your problems, or at least getting that way. Replace em all while u got the down time? It would be a very good idea to get new ones anyway.

You ever check your Fuel pressure regulator? That could be causing your stumbling and the fouled plugs from before. Then again i could be wrong, wouldn't hurt to check it out.

*edit* i didn't check this article to see if it answered your pre ignition/detonation questions but it's pretty long. Migh have some useful information to help you figure out wtf is wrong..
http://www.contactmagazine.com/Issue54/ ... asics.html

[McShanks]

Thanks kickedin! I have actually considered the fuel regulator as well, and plan on replacing that. I will do that before the IACV since it is cheaper/easier to replace. My 5.3 Vortec plans are on hold atm since I am going through a legal separation. After that legal crap is done, it should actually be easier to do the swap, both financially and because I will have more time.

[TTkickedin]

OOH, another one for you. Have you replaced your fuel filter?? That little B**** caused SO many problems on my subaru one time. I didn't even think of changing it, but someone suggested to do it and I changed it and it had no more problems. Very easy fix there, sir.

Can't remember if the symptoms were as you described but it would definitely be a good idea while u got the down time as well.

Hope your separation goes as planned. Good luck

[McShanks]

Wow! I didn't even think of that... Gonna do that tomorrow before I order the regulator.

[McShanks]

Ok, did the fuel filter and it worked great! I drove it around for a while and let the engine warm up, no issues at all!

...

Until last night, when it did it all again. putt-putt while idling cold. Sluggish between 2000 and 3000 RPM and light throttle. But today, it didn't. So. Weird. I know it is not the dreaded worn head/cas issue that there was a TSB for requiring a head replacement. If it were that, then the timing would be off drastically and impossible to adjust properly, according to the TSB. But the timing is fine, and it only happens sometimes. It also doesn't seem to matter if the engine is hot or cold. So, I am thinking it has to be a connector somewhere, or something loose like a vacuum line. I cleaned/di-electric greased all EFI, Coil, TPS, PTU, CAS connectors. Is there anything I missed? I guess I should check the ECU connectors, and I am going to get a pressure gage for the fuel. The car also will not idle at the same RPM twice. Sometimes it is around 800 RPM. Sometimes 1000. Sometimes 1300. Sometimes, it seems like it is trying to die and RPM drops down to about 600. I make sure all accessories are turned off like A/C and lights/stereo, etc. I am still thinking it could be iacv, but is there anything else I could check before I put money into that? Since it only seems to happen about 50% of the time, I feel like the car is taunting me....

I just want it to be all better...

Another note, is that it seems that if it does this stuff at startup or shortly after, it does it the whole duration of the drive. If it does not do this stuff at startup or during warmup, it does NOT do it during the duration of the drive. I wonder if that means anything?

[TTkickedin]

Yeah from what I've researched, I think your problems derive from the FPR.

The symptoms of a bad fuel pressure regulator include:
Lack of fuel pressure, excessive fuel pressure, black smoke and rich engine running condition, instant drop of fuel pressure once the vehicle has been turned off, delay building sufficient fuel pressure.


You should also check out the Fuel Dampener, or Fuel Accumulator while you're at it. This is a pretty weird problem so you have to cheak all the possible options here.

Check your fuel pressure for proper numbers, (

http://www.z1motorsports.com/product_in ... cts_id=639

Here's where Everything fuel related is located!!!

http://www.plantbonz.com/cars/photoguide/fuelsys.html

[McShanks]

Great info, thx Tkickedin. I need to find/make a tester for fuel pressure. I will give it a shot this weekend.

[TTkickedin]

No problem man I'm here to help! Any progress on the issue?

[McShanks]

No progress. I have some other personal issues I am dealing with currently. Car has been running great the last few days, though. I am still going to test the fuel pressure asap.

[TTkickedin]

Hows the progress on either of the issues you got? (the separation and the fuel issue)

[DCaff300ZX]

I'm interested in followups too, have been waiting to hear about these exact symptoms for over a year now and was at the same point as you before I gave up- fuel pressure regulator and dampener.
I will be replacing the reg and dampener and all hoses and PCV soon, hoping like HELL this fixes the mysterious problem...but want to hear about what the OP is experiencing.

[TTkickedin]

Dcaff Check the link i provided with the fuel system parts list, make entirely sure you aren't missing anything on there. Another good idea to cure fuel related problems when nothing else seems to be working to replace all of the hoses as these can become restrictive or clogged. Or, you can always relfash your ecu/get a new one if that doesn't nseem to solve the issue.

Any chance that the gas tank may have gotten rusty from sitting with an empty tank? This is something a mechanic friend of mine told me about; Fuel Additives such as fuel injector cleaner, can also damage the tank - IIRC Nissan used some special lining in the gas tank that fuel additives tend to chew at. Don't get me wrong, fuel injector cleaners are good for our cars, (especially if the old style injectors are being used with this new ethanol gas,) but the additive should only be put in on the hose right after the fuel filter to prevent gas tank damage.

Hope all this info helps!