Hard vibration while at stoplights

[Trimble Epic]

OK, car is 93, NA, automatic trans.

I had a problem with a misfire, but recently changed out all the plugs (PO has wrong sparkies, of course...) and I replaced all the coil pack connectors.

So, the misfire is gone, and normally(while moving or in park), everything seems fine... It's not really idling rough or anything, it's just that at a stoplight, with the transmission in drive and it's idling, the car (only sometimes) vibrates hard. My wife's complaining about it and says I should check the motor mounts. (she's not really a car person, but she likes to think she knows some stuff)

edit: I originally said it's a rough vibration, but it isn't really rough.. it's smooth and consistent, it's just hard. but as soon as I get on the gas, all the vibration goes away and it's smooth.

I'm not sure how to chase down engine vibrations. The motor seems healthy and runs smooth, except when it's in drive at a stoplight.

I tried to go back to the "everything you need to know about the z32" thread and re-read the "Having idling problems? This should help!" links, but it looks like those links are now dead... I hope someone has an archive! (I think I may have printed out those pages somewhere).

Help! Should I be pulling codes for this?

[sx moneypit]

Your wife may be correct.I would check the motor and transmission mounts.

[marcyprojects]

Had similar symptoms with my 90 NA manual. Had one injector get stuck closed, I tapped on it with a hammer(yes this is no lie), my misfire went away but was still hard sometimes. I put some marvel through the tank and its seemed to clear it up. I used a harsher fluid when I first started to have idle issues and I think it may have left some stuff behind.I thought to use marvel it since itis a cleaning product, but it is somewhat oil based so it lubricates as well. Helps keep injectors from sticking. Cheap and easy fix, try a half a bottle in the gas tank with like a quarter tank of gas and see if that helps. If it does you may have to treat the car a few times to get the results to stick.

[Trimble Epic]

I drove my car for a couple hours yesterday and I guess i'm not entirely convinced that the problem isn't actually a misfire... I'll do the power balance test this weekend when I can get away from my daddy babysitting job for a few hours...

I recently replaced all 6 plugs and refreshed the plastic connectors... I'm not entirely sure how to power balance test those two plugs under the balance tube... it was a pain just to get to them with the engine off, I'm not sure how I'm going to get to them while it's running... but I'll find a way, I guess...

What I can't understand is - if I have a dead cylinder, how can I be getting ~20 mpg? wouldn't my mileage be in the toilet if one was down?

[sroy123]

I have this exact same problem with a 2001 Xterra. EXACTLY. I have been working on it for over a month now trying this and that. So far I have replaced all my plugs, both coolant sensors, distributor (which has a cam sensor, main coil, and some other goodies inside and it came with a new cap and rotor), cleaned my Mass air flow sensor and changed my trans fluid (its an automatic). No change. I can get it to duplicate when the truck in in the driveway in gear. On mine I hear a click then the engine goes to rough and another click and the engine clears back up and purrs this continues like that until I shut the motor off. Almost like a bad a/c clutch clicking in and out. No engine codes either.

Now here is what I have done to mostly clear it up. I have ran a complete can of B12 chemtool spray through the idle control valve intake hose while the engine was running and it has cleared it to about 80 percent better. I ran it thru with the engine cold to get max cleaning. While I was at it I ran it through the throttle body. It thru a code but I reset it after. Like I said it is much better but not perfect. I think my idle control valve has problems that can't be completely solved by spray. My valve makes a hum sound when the ignition is on and the engine isn't running. So I am pretty sure that isn't a good thing. The problem with the xterra Idle control valve is that it is on the underside of the upper intake manifold. I am not real excited about taking that off. Please post back and let me know if this helps you solve the problem. Or if it doesn't post back anyhow. Because it will help me with my Xterra.


Also this problem came up the same time I got my new (to me) 300zx convertible. I am a lot more interested on working on it than working on my wife's crappy xterra. LOL. Good luck.

[Trimble Epic]

Ok, ok, I was wrong. it's clearly misfiring. I did the power balance test, and the middle cylinder on the passenger side is not responding to pulling the coil connector (no change in engine idle like the others)

So, I started troubleshooting. I swapped the coil pack with a working cylinder. no change, the same cylinder is dead.
I tried holding a long screwdriver on top of the injector, and I can hear a clicking/tapping sounds, exactly the same as a known good cylinder.
I pulled the plug and looked at it. I just changed all the plugs a few days ago... The plug looks somewhat clean, and more importantly dry... I If the injector was really firing, wouldn't the plug be wet? I wiped some soot off, but the plug is pretty much clean. I fear a bad injector... Time to look up how to ohm test the injector... Sigh...

Can someone remind me of the other steps to troubleshooting a dead cylinder?

Oh, one more thing... I have an obviously replaced PTU with that subharness thing, and the connect was not fully plugged in (was sitting diagonally).. I can't imagine the car would run right at all if that was not connected right, but what if just one end of the plug wasn't making good contact? I fixed the connector so it's now fully engaged and no change in the idle... so that's not it.

So for the moment, I'm back to suspecting a bad injector... If I have to replace an injector, does that mean a plenum pull? Sigh... I don't get a lot of time to work on the car, but the wife wants to take it when we go on vacation in 4 weeks... I need an idea of how much work it's going to be to fix an injector...

[Trimble Epic]

Update...

So I checked the injector... 33 ohms. @#$%

I'm now in the middle of plenum pull... taking a break right now (as the guide recommends heh)

I had to stop and go buy some hose pliars. I damaged the brake vaccuum booster hose pulling too hard... (or, perhaps it was already heat damage if it ripped that easily). I suspect I'll be replacing a lot of hose on this thing

But I'm half way down to the injectors now. I'll have to do the TP water line delete, and I'm tempted to do the EGR delete kit too... I haven't got the EGR pipes undone from the bottom of the plenum yet, but that looks like it's going to be a nightmare. sigh.

I do have one question that I can't seem to find an answer to: I've read post after post and watched several videos about popping the injectors into the fuel rail (making sure to use PLENTY of lube to get them to pop in right...) but my question is this:

What seals the fuel rail to the intake? I've seen videos with the fuel rail off, but I can't find any video of anyone reinstalling the fuel rail. Is there a gasket? o-rings? press fit? what up? It must be sealed somehow, but I can't find the information.

[Trimble Epic]

So, I did some more work... My next step is to remove the 8 bolts holding down the plenum. I could swear I saw a post suggesting that they should be loosened in the reserve order of tightening them... but now I can't find the tightening order... (just "spiral starting from the center")..

Anyway, I wanted to post to say removing the EGR tube bolts was actually very easy.. they weren't in there very tight at all, so I popped them loose with a small 10mm wrench, then finished them with a (very) stubby 1/4" drive ratchet and socket... I had to use an extension long enough to come up from below... thank god it's not a turbo (did I really just say that?)

I'm very tempted to delete the EGR, or at least delete the pipes to the plenum and then disable the valve... but I can't seem to find any information on whether or not deleting the EGR actually affects either performance or fuel economy... I would really love to know if the EGR system actually helps or hinders fuel economy, that would be my driving decision maker... I've seen posts (about other vehicles) that deleting the EGR actually reduces fuel economy? If that's the case, I'll keep mine.

Oh, and another curious thing... I found that the two bolts on either side of the engine that attach the plenum to the engine brackets are all gone.. all four bolts were missing. So, perhaps someone at some point removed the plenum before, and forgot those bolts? I'll want to replace them, but it looks like the brackets aren't aligning right, so maybe thats why they were left off? or maybe my plenum is bent... Arg!

3 weeks until this car needs to be running again... clock is ticking and I only get a few hours at a time to work on it.

[Trimble Epic]

Arrrrg!!! so close...

Plenum bolts are out, it's loose and rocking around, but still stuck... it's those damned water lines that we all want to delete... Those and the PCV hoses... I'm thinking I should just cut all of them and replace the PCV hoses... they are rock hard anyway, so they probably need to be replaced...

Alas, my family is all catching a cold... my sinuses are flooding, and I just know once this hits, i'll be in bed for a week and I'll forget where I left off on the plenum pull... sigh.

I ordered a set of injectors, and I'm prepping to order the o-rings, gaskets, etc. Btw, if I keep the EGR, do I need to replace the EGR plenum gaskets? or are they reusable? they look to be reusable...

ArrrgGGG!!1!

[ThisIsSparTTa]

Cut the water lines. Do the bypass. Replace the PCV hoses. It's a small investment to save a lot of headaches in the future.

I'd replace the EGR gaskets to avoid headaches in the future. Especially if those are potentially the ones from the factory. Maybe if they'd been done recently then reuse them.

I have a few laying around I could USPS snail mail you in an envelope if you send me like $5 Paypal. PM me if you want em.

[Trimble Epic]

Yay! The plenum is off! and wow, I found some missing bolts under it... one missing original bolt from the balance tube, and at least one coil pack bolt(green below) (actually might both be coil pack bolts - two of the coil pack bolts are different... Suspect someone swapped them..) Also, some misc trash, who knows how long it's been... part of a coil pack connector (yellow), probably part of harness holder (blue)



Anyway, that was a b****... NOW I understand why we all do the TB coolant bypass. Add me to the list.



So, I guess I can do rubber bypass caps here (three red above) more trash laying around (yellow). The fourth cap goes over on the Driver side... NOT looking forward to getting to that one...

Ok, after some pondering over the photos in the Wiki, it's now clear what to do with the two vacuum lines. I think I'll just leave the hidden gallery on the underside of the driver's side of the plenum in place and just use it for the vacuum hardline to the carbon canister. I'll need to run a new line for the EGR on the passenger side though. I actually broke the EGR vacuum line(green above), I didn't realize it was part of the PS coolant line gallery. I'll have to replace that line. (@#$% getting to the EGR valve nipple doesn't look like fun...)

Then again, Now that my plenum is off and I examine the EGR system... mine is COMPLETELY clogged. it looks like this on both sides.

So, basically I've been running without EGR since I got the car. I'm wondering what affect that has on the performance, if the ECU thinks it's working... (then again, the ECU adjusts itself based on the O2 sensor, right?) I'm pondering doing the partial delete to at least closeup the plenum, but I'm not sure if that's really the way to go. I really don't want to try to FIX the EGR, as I really don't want to have to dig down to the EGR valve on the back of the engine... but, if I don't delete it, I'll at least have to get a new vacuum line down there... (unless I junction the existing line that used to connect under the plenum.. hmm.. that WOULD be easier by FAR... I think I'll just do that.

So, this whole job is happening because I found an injector that ohm's at 33 ohms... (111 ohms when I rechecked...) I ordered a set of injectors from that seller on eBay (TLFperformanceparts). They look good, and seem to have included the o-rings... At least, I'm assuming they are new o-rings... if anyone else has used these guys, is it safe to assume the o-rings are new? I ordered a set from Z1 already, so I can change them if I need to... I only needed one, but I got 6 and I'm wondering if I should replace them all with the new set (TLS says they are "flow matched"?) Anyway, once the plenum was off, I found this:

So, I guess it's back to the ordering page at Z1 heh... but I need to decide what I'm doing with those EGR tubes... new gaskets? or blocking plates? Not sure which way to go yet. I'd love some commentary on that. Oh, and I think I'll order a new PTU connector kit; I have the subharness and it's ugly. It's not causing any issues yet, but since I disturbed it for this work... who knows.

Anyway, now that I have some photos uploaded, I need to go back and add photos to my other posts.. hahaha broken promises need to be fixed.

[nexus08]

Nice job with the photos! They really help.

If you have a full set of new injectors I'd go ahead and put them all in. If one is bad, probably only a matter of time before another goes out.

Maybe keep a couple of the old ones that ohm out nice as spares.

[nexus08]

As far as the EGR goes, I've read that it does improve performance and MPG a tad. I think it has something to do with a slightly cooler exhaust.

But most importantly, it helps reduce NOx emissions.

If you are in a state like Cali where they do NOx testing you may need it functioning to pass emissions (others can speak to that.. I've heard you can pass without it).

If you are in a state that doesn't test for NOx (most just measure CO and VOC) you can probably get by without it.

[Trimble Epic]

I'm in North Carolina, and here they don't even check emissions if they can't just plug into an ODB II computer... so I'm exempt.

So, I could delete the EGR without any issues, but if EGR actually HELPS fuel economy, then I might rather keep it... if I can unclog the @#$% things... I went at the drivers side tube with a pick and a vacuum cleaner to see how far down the blockage goes... it's pretty bad... I might need an actual pipe cleaner from my children's crafting supplies to actually clean a pipe for once...

But, I'm concerned about knocking all that s*** loose into the pipes, knowing that on startup, some of that crap (that I can't vacuum out) will get sucked into the intake and down into my cylinders... Will that damage my engine? or will it flow through/combust without harming the engine? Yikes!

[veery]

Make a vacuum adaptor with a piece of rubber hose fine enough to fit in next to your pipe cleaner and suck out the debris as you loosen it. Think dentist's office.

[Trimble Epic]

So... This thread is due for an update!

So, my car is back together and running smoothly again. Actually, she's never been this smooth as long as I've had her... I suspect she's been misfiring (or occasionally misfiring, or even partially misfiring) for a long time, and I just hadn't noticed how bad it was. I'll get to that at the end.

First, lets talk EGR. I decided to just leave it as is, clogged. It's basically disabled without the ECU knowing that it's disabled. Being clogged, I don't have to worry about any exhaust gasses getting into the plenum at the wrong time, at all. If I ever pull the motor out completely, I'll pull the EGR tubes, clean them out, and maybe replace the EGR valve. I'd like to have the bonus fuel economy. The system is actually pretty simple from a number-of-parts perspective.

I mentioned above that I had ordered a fully set of 6 injectors. Well, I went ahead and installed all 6 new injectors (well, new from eBay seller TLFperformanceparts.) I can now report that they all run smoothly.

I showed above the cracked cap on #6. I had ordered a replacement fuel injector cap from Z1. I thought it might be just an idiot mechanic that broke it during the previous injector replacement (the job that left the shrapnel all over the place), but as I discovered, it was actually something much more sinister...



After I installed all 6 injectors in my existing fuel rails, I installed the caps and tighetened them down... cRAcK! I recycled an old cap onto that #6 injector, and it instantly cracked, just exactly like the one I found cracked in the first place. After further examination, I discovered that my fuel rail is defective. I say defective because I honestly can't imagine how a mechanic could have caused this damage. It's the inside flange for #6. Have a look at these photos and try to imagine how this bend could have happened... I can't.






So, I ended up buying a used half-fuel rail, and moving my injectors over. But damnit... Now I have to press out these brand new injectors and damage the little plastic caps on the injector tips. #$@# I HAD to come up with a way to push out an injector without damaging those SOFT plastic caps...



Voila! Here's how I did it. NO DAMAGE to the caps! I grabbed an old set of feeler gauges, pulled out a nice flimsy one, and rolled it up. I trimmed it, but it did fit very nicely into the fuel rail around the injector cap, just enough to let me tap out the injector with a soft-face mallet without ever touching the soft cap. Victory! I'm keeping that rolled up feeler gauge and adding it to my special selection of tools for my Z



So... I got three injectors popped back out of a bad rail, re-oiled, and popped back into the replacement rail. Installed the 5 new rail seals, bolted down the fuel rail with a span on new gates fuel line between them, and started buttoning up the engine. Plenum back on, wiring back together, everything. I took my time to get all the wires right, all the vacuum lines on, and I was ready to test.

To relieve the fuel line, I just pulled the fusible link for the fuel pump next to the battery. It really is the easiest way to do it. After reassembly, I replaced the fusible link, put the key in and let the fuel pump pressurize the line. I found a leak at filter because I forgot to tighten those clamps. I fixed that, and was ready for first start.

She started up pretty easy after 10-20 seconds of cranking (I assume the fuel line needed to purge air). Once she was up and running, ... wait.. she's still missing. @$##^%#$^%@$#% Arrrggg!!! I pulled the coil on #3, the cylinder that was missing previously, and yup... no change. So that cylinder was still dead. I was PISSED. I have spark, I have new injectors all around... I feared the worst, that maybe the compression on that cylinder was low... oh god... nooooo...

I decided I needed to prove the injector was getting a signal from the ECU, and so I went to my computer to research... Found this thread, and decided I was going to have to try this CAS trick with a 12v LED stuffed into the #3 injector connector to check signal to the injector. It was midnight. I walked out to the garage to look a the timing belt cover to see how hard it was going to be to ... wait.. what is that... on the floor... OMG NO.. NO.. NOooooooooooooo

Ok, did you catch the foreshadowing? It wasn't a typo. I said above that I had installed the fuel rail seals, all 5 of them... wait.. there's supposed to be 6. WTF. I just found one on the floor. a brand new one. how the @#$% did this get out of the engine?? I was sooo careful putting the fuel rail back in, I was sure I had all 6 seals in place. Obviously, I had dropped one. I even inspected with a flashlight after installing, but somehow I missed one. Now I'm REALLY pissed. It was midnight, so I went to bed.

I woke up at 5 am unable to get it out of my head. I got out of bed, coveralls on, in the garage, cleaned away the debris from the night before, and was wrenching by 6. By 9am, I had the plenum back off and was down to the fuel rail again. (YES, YOU TOTALLY SHOULD DO THE TB WATER BYPASS. It's not even a question.) You've GOT to be kidding me. It's #3. The cylinder that started all this @#$% is the one that lost it's seal. 2 minutes later and the seal was back in place, and the plenum ready to go back on. I found one more fascinating fact... The plenum gasket showed a little wetness at the edge of the tube going to #3. Gas? yup. It seems that with the seal missing, the vacuum leak AT the injector actually causes the fuel spray to get sucked back up into the plenum and down into other cylinders. Holy crap. That totally explains the misfire, even with perfect spark and fuel.

3 hours later, and I'm ready to turn the key. (Did I mention that you should totally do the TB water bypass? I feel I should mention how easy it makes things...) Fuel pressure test and leak check, and ready to start the engine. She starts up. Firing on all 6. OMG. That was it. A missing rail seal causes a misfire. She's purring. I'm smiling... and I get curious.

When I took out the old seals, they looked like @#$%. Torn, cracked, split. I think that may be where the misfire started to begin with. Have a look - these are my old seals. Knowing what I know now, I suspect that these could be the source of mystery misfires for all of us. Have you checked yours lately?





Moral of the story - If you have a mysterious dead cylinder, and you pull your plenum, Check your rail seals.

I hope this helps somebody!