Need Help

[troy300zx]

I just finished pulling my plenum, changing out all of my injectors, wiring in new injector and coil pack connectors and changing out all my old vacume and water lines for new. Got her all back together, fired right up but as soon as I step on the gas she bogs down and backfires up into the plenum. Seems like the timing is out of a huge vacume leak but can't figure it out. She ran fine before I started all this except for the #5 injector went bad. I did use rebuilt stock injectors and one thing I noticed when I had her all apart were that my EGR tubes that went up into the plenum were all clogged with carbon and such. I did clean them out so you could blow through them. NEED HELP!!

[CrazedZ32Owner]

did you re-check all of your vacuum lines?? also did you use a new upper to lower plenum gasket?

[troy300zx]

I checked all my vacume lines and used a new plenum gasket. I don't really hear any vacume air. It just seems like I have something backwards like a plug wire, but with having the coil packs all should be correct.

[Z31toZ32]

try running the codes and see what it spits out.

[troy300zx]

That's the plan for when I get home. Just wondering if some of my wiring did not turn out. One thing I thought was odd when I wired in the new injector connectors was that on the original injector connectors, the negative wire was thicker than the positive wire and on my new injector connectors the positive wire was thicker than the negative.

[Z31toZ32]

polarity is not an issue on the injector connector wiring. as long as you have a "+" and a "-" in any combination on each of the injector connectors you should be good.

[troy300zx]

That's good to know. I will run the codes and then start looking at the injectors to make sure they are all ticking. I Read a write up that talked about testing them with a 9 volt battery with the motor off. Sounded interesting, but wasn't sure of the validity. I may try that once I research it a little more.

[GerryO]

Have to ask if you also have all of the intake ducting connected, along with the MAF, and if you've also checked/cleaned the AAC/IAC valves, the Air Regulator and the EGR valve now that the tubes are clear?

All new o-rings on the injectors and fuel rails, no signs or smells of leaking fuel, and you've ohm checked the injectors?

Lots of good info here:

http://home.swipnet.se/e-solutions/IdleTech.html

http://home.swipnet.se/e-solutions/IdleTech2.html

http://home.swipnet.se/e-solutions/Contactclean.html

http://home.swipnet.se/e-solutions/Vacuumleak.html

[troy300zx]

I am not smelling any fuel or seeing any signs of leaking. I did all new injectors and seats for the fuel rail. All intake piping and MAF is on and connected. I did not clean the the AAC/IAC valves, the Air Regulator and the EGR valve. I was going to replace the EGR valve when had it all apart but from what everyone says it's a real pain with the motor still in the car. Do you think it could be the EGR. Didn't get a chance to run codes or check the injectors tonight but fired her right up and she sounds great at her high idle. It's just the low idle where you hear a miss and as soon as you rev the motor it starts to backfire into the plenum, not out of the exhaust. It will continue to rev and once you get into about 4000rpm it sounds good again.

[GerryO]

I am not smelling any fuel or seeing any signs of leaking. I did all new injectors and seats for the fuel rail. All intake piping and MAF is on and connected. I did not clean the the AAC/IAC valves, the Air Regulator and the EGR valve. I was going to replace the EGR valve when had it all apart but from what everyone says it's a real pain with the motor still in the car. Do you think it could be the EGR. Didn't get a chance to run codes or check the injectors tonight but fired her right up and she sounds great at her high idle. It's just the low idle where you hear a miss and as soon as you rev the motor it starts to backfire into the plenum, not out of the exhaust. It will continue to rev and once you get into about 4000rpm it sounds good again.

Probably a bad plug (all OEM?) or coil pack, and not an injector. Disconnecting and reconnecting wires to the coil packs one at time at idle will tell you which cylinder is the culprit (= no decrease and increase in idle speed).

An injector that isn't delivery any fuel, would cause a miss, but not back-firing, which is an indication of air, fuel, but no spark/ignition in the problem cylinder.

Higher engine rpm speeds will hide the problem, similar to new fuel saving routines that don't feed and fire all cylinders at highway crusing speeds.

[troy300zx]

I was thinking it was spark too just because I installed new plugs gappd to .044 and spliced in new coil connectors. Thinking maybe I goofed something up. Had to leave out of town so all the investigating will have to wait until Sunday or Monday. Thanks to everyone for your help. Keep it coming if you have any more ideas.

[Ace2cool]

What brand of plugs and what type did you use? These cars are VERY particular about what plugs they like.

[troy300zx]

I used NGKs that I got from Z1 so I am Assuming they were the right plugs but I did not double check.

[BigTDogg (MA)]

Did you remove the fuel rails in this process or just replace the injectors with the rails still mounted to the lower plenum?

[troy300zx]

I removed the fuel rails when I changed out the injectors. Last night I did a few things that did not solve the problem. First used the long srewdriver method to listen to all of the injectors and they are all working. Also changed the spark plugs back to the ones I took out, but no change. Tried switching a couple of vacuum lines thinking maybe I mixed them up but no change. This is driving me crazy. It just acts so much like a vacuum leak or like I crossed some wires that these cars don't have. Fires right up, idles with a miss, As soon as you press on the throttle it bogs way down and sometimes back fires. If I depress the throttle very slowly, it does not seem to bog down as bad, has an occasional backfire into the plenum and lets the rpms rise. Once I get to about 4000rpms she's revving away and sounds great. Very confused as to what the problem is. I still need to check coil packs and also wondering if one of the new injector O-rings maybe got pinched and is letting too much fuel by. Hope to get a pressure gauge on the vacuum and fuel within the next couple of days. Open to any suggestions.

[NolimitZ32]

Sorry if I missed it but are you getting a CEL or codes? some codes wont trip the CEL

[nissanfreak12]

Have you tried pulling each plug and seeing if one looks different, like more sooty or even wet? That should tell you right away if you pinched the o-ring. If anything try the pressure test or even a smoke test if you can get your hands on one. Are all the plugs connected completely with no corrosion on them. I know these seem like "I am sure these are connected", but when your frustrated they are easy to over look, trust me been there.

[GerryO]

I just finished pulling my plenum, changing out all of my injectors, wiring in new injector and coil pack connectors and changing out all my old vacume and water lines for new.NEED HELP!!

Back-firing suggests that unburned air/fuel is igniting in the wrong location (not in a cylinder), which probably means no spark. Disconnecting and reconnecting each coil pack with the engine idling should result in an idle speed drop and momentary surge when it's reconnected, if the coil pack/connection/spark plug is good and the cylinder is firing correctly. Isolate the problem cylinder and go from there. Swap coil packs to confirm and inspect/test rewired connectors. Check the timing with a timing light.

If an o-ring was pinched there would be noticeable fuel leaking to where it doesn't belong, possibly to the point of hydro-locking the problem cylinder. High rpm speeds will mask a firing miss. The spark plug in the problem cylinder could be pretty fouled by now and may need replacing.

[troy300zx]

Ok, we are making progress. Ran the fuel pressure check and she held 45lbs the entire time the care was running. So I thinking the o-rings on the injectors are probably fine. Plus not getting excesive exhaust or smoke. Decided to pull out my computer and swap it with one that I had from a california car. Fired her up and the she is no longer bogging way down when I rev her up at idle. Still has a miss though and get a small backfire every now and then, but night and day difference in the way she was running. Was able to take it around the block and out onto the highway, but still has issues when accelerating. It seems the slower I depress the throttle the easier she will accelerate. If I try to floor it while driving she bogs down. Does not bog down when I floor it while idling. Swapped out the PTU with an extra one I had but no change. Thinking now maybe have a Cat or two clogged due to the bogging down while under a load. Also, I must have fried my computer when I first started this whole project. I had her sitting in my garage all winter and the battery had gone dead. So I threw a charger on the battery and jumped her. If that is how it happened, does anyone know off anything else that tends to get fried when the computer does?

[GerryO]

So much fun. Pulled my plenum a couple of years ago at 170K miles to replace all six injectors, spark plugs, PCVs, EGR valve, etc. Also did the throttle body heating delete, and thoroughly cleaned the EGR tubes and MAF. Put things back together with my son's help; he had the passenger side of the plenum. Connected one O2 sensor to the KS and vice versa, and it took me a while to figure out that my son didn't connect the EGR lines.

Several codes, and a lot of thinking, inspecting and adjusting (CPS and TPS) later, all was fine and is still good. On one wet, damp morning the car started and ran very rough, but things quickly smoothed out and it's never happened again. Suspect it was wet, damp injector or coil pack connections, even though most connections got dielectric grease.

Not too longer after an O2 sensor started acting up so I replaced them both, improving fuel mileage. Still haven't replaced the length of metal tubing that heats the Air Regulator to pull the idle down while driving after cold starts.

Previous to all this the car sat a quite a while, waiting for water pump, timing belt, etc replacement. Have always tried to avoid jump-starting, preferring to simply charge batteries over night and if they don't hold a charge, they're bad. Weak batteries can cause strange behaviors.

Given the whole individual coil pack on spark plug and CPS distributor-free design of these engines, they should and can reliably purr at the lowest idle speeds. Best of luck.

[troy300zx]

When you were adjusting your CPS and TPS, were you using a timing light or just going by ear?

[GerryO]

When you were adjusting your CPS and TPS, were you using a timing light or just going by ear?

Snuck a small strand of copper wired into the backside of the TPS connector to measure/set the TPS output voltage to 0.38 VDC, then adjusted the timing using a timing light and finally adjusted the idle speed with the engine fully warmed up and no load on it due to PS (wheels pointed straight ahead), AC or the alternator.

Believe after output voltage adjustment the TPS connector needs to be unplugged and plugged back in while to engine is running, in order to register the new throttle closed output voltage in the ECM and prior to idle speed set screw adjustment.

Also had cleaned the throttle bodies.

[Ace2cool]

Spitballing here, but did you check the connection on you MAF? That sounds like what happened when I forgot to hook my MAF back up after doing the filter on the TT. Would run perfectly in lower RPMs, but as soon as I gave it any amount of throttle, it would bog and shudder.

[troy300zx]

I never had to unplug it, but I will check it. Also may look into whether it is bad. Any idea on how to check those?

[es.biggs]

Have you ruled out vacuum leaks? I don't know if it would cause a backfire. What about the o-rings for the balance tube that runs across the top of the plenum near the firewall? If you are missing one or if one got pinched it could cause a nice leak

[GerryO]

http://www.kroffts.com/kke/files/Nissan ... Manual.pdf