Okay me and the mechanic are fed up with this. My bros car (my old 95 5-speed) has been having problems for a while now. Recently it has gotten worse, it would take a lot of cranking to start it, and would backfire a lot.

Now it hasnt started in over a month. It cranks and the RPMs rise to 1200-1500, but it has simply refused to start in 5-6 weeks.

Weve tried almost everything now. The 2 crank sensors and the Cam Sensor have all been tested and re-tested, we replaced all 3 with DE-K sensors, didnt change anything at all. All of the wires from the sensors to the ECU have been tested, all three sensors were grounded correctly. We made a super overkill DIY grounding kit. All 6 spark plugs were changed.

We changed his 96 auto ECU with a 95 5-speed ECU and it didnt change a thing. With the 95 5sp ECU the only code is a 047something code for the Crank REF sensor on the pulley, which indicates a timing problem.

And a timing problem there definately is. While cranking only one or two of the coils fires once in a while at random. We switched the coil packs from one location to the other and it changes nothing so I assume the coil packs are okay.

We even changed the Fuel pressure regulator, the fuel filter only has 5500 miles on it and it is a brand new 300zx one back when I did the 3.5 swap.

The engine wiring harness is completely untouched, and why would that be the problem, anyway? When it had the stock 3.0 in it never did that, with the 3.5 in it smelled like fuel but ALWAYS started quarter turn. The problems only started when we put this junkyard VQ30 in, so the problem most definately looks to be with the motor itself (well something on the motor).

Internally I think its fine, it runs great when it actually runs and went 14.9@95 mph with full catback and y-pipe. So all points to something about the injectors or coil packs I think.

Its been backfiring at random and stalling randomly at a light from time to time. What the hell is going on? We even checked the crank pulley to see if the timing marks were damaged. It just completely refuses to start. All 3 crank-cam sensors were tested and re-tested as per the Haynes manual.

Any ideas?

 

i am going to go with Injectors on this one.....When I had my 3rd gen i had a leaking injector and it would cause extended starting eratic RPMs at times...and stalling...but listening to them it sounded like it was firing normal...so i was dreading the wiring....the dreaded thing is if the wiring in the harness to the coils and injectors have some breaks in them.....good luck...hopefully its not wiring at all

 

We havent touched the wiring harness at all and this winter when it had the 3.5 in it, it hadnt ran for 5 straight months and started RIGHT up. The next month we put this motor in and the problems started.

Also, I am VERY tempted to blame the injectors but why would they cause the super erratic timing? That alone points to an electrical problem, right?

 

I agree that injectors would be the next thing to check.

 

Yes, do a audio injectors diagnosis first. You'll probably have a hard time with the rear injectors.

If injectors aren't it, without CEL on the sensors, I'd tell you on 95% chance that it's timing off by a tooth or so (perhaps, jumped?) From the way you described the problems, it sounded really much like a timing problem to me since I've had so many during my past installs.

-Peter-

 

I really dont see how the timing chain jumping a tooth could do this, it would at least start and run like **** but it would start at least. Run rough, perhaps. But like I said when this engine runs, it runs with the normal power of a 3.0L and all. When you mash the pass pedal it pulls exactly like it should and doesnt sound or run wierd at all and Im pretty sure it would run a lot rougher if the timing chain had jumped a tooth or two. We changed the tensionner a while back to cure the 95-96 chain rattle problem.

Also, the mechanic has a hard time buying that the injectors could cause all this erratic timing crap. Anyone can guess a relation between the timing and the injectors here?

 

everything cool with the timing ring on the flywheel? by eye does it look to line up with where the sensor tip would be?

 

Yeah I just checked that with a mirror. All teeth are aligned just fine. Also, all the white wires from ECU to crank and cam sensors are fine too.

 

this is unlikely but it happens on dirtbikes alot and it stumps many people when it happens, from improper installation the flywheel key sheers and causes the spark to be random and intermitten and every now and then it will 'catch' and the thing will rev up somewhat ok but at idle it will want to die every few seconds and backfire

 

Well im looking at the small crank POS harness right now. I just put the 5-speed ECU back in, reset it, tried cranking it a couple times, and the only code showing is 0802, which is a crank POS code. Now that sensor was tested approximately fourteen times and is clean and free of magnetic crap stuck on the sensor.

I just read a thread where someones 4th gen shut down on him and he had to get it towed to the dealer. Only code was a 0802. They cleaned the harness connectors (he had started polishing his valve cover and aluminum shavings got in the connector since it was unplugged). His car started right up.

That small harness (one ground, one positive, white pulse wire that goes to the ECU and a fourth thats a ground shield) is only 37$ cost at the dealer so we may order it to get it tomorrow.

 

Two words...timing light. Get one and check the base timing. That's if the new CPS (POS) subharness doesn't fix the issue, of course.

 

Battery's charging right now. Its a little weak. I just re did the DIY connections on the current harness and cleaned all connectors. Car backfired on me (somewhat violently) when I cranked it. Not pleasant at all.

That harness is the only thing that has been modified. The original 95 5-speed engine wiring harness has not been touched at all except for Jime's manual fan switch mod a year and a half ago. I had to re-do those connections a while back because I was using the 2002 Crank sensor on the 3.5 (to avoid having to grind the block) except those were welded with a gun. The current harness was not. So I think it would be wise to change this sub 40$ part before going any further.

On a positive note tough, we were lucky enough to find a VLSD 5-speed that actually works when we changed the trans. Its from a 98 and has only 111,000 kms on it (a little under 70,000 miles). The junkyard that sold it to us thought it was an open diff so we got it for 450$cnd, but only the VLSD driver axle would fit and with the car on the lift both wheels turn 1:1 together same direction. Traction has noticeably improved.

 

It still seems like a timing issue to me.

-Peter-

 

It definately is. But if the wires from the main harness to the sensor arent clear, that could cause random, erratic timing. You know how ******* picky our electrical systems are towards grounds and crank-cam sensors. The 9 planets have to be aligned for everything to work perfectly.

 

Okay I teared down the timing assembly (with the engine in the car! What a pain in the @ss! Ill never own another FWD car again) and reset timing PERFECTLY (like we do on 3.5 swaps). Not only that, I checked both secondary cam chains and both are set perfectly too. Changed the tensionner & guide for the 97+ upgrade. Also changed the small secondary tensionner for the 2 cams on the front bank. Then re-sealed everything and put 4.5 quarts of oil in it.

Then I changed the Crank POS sensor, its small subharness, and the Crank REF sensor.

With the MT ECU, I only get code 0505 which means nothing is wrong. With the AT ECU I get 4 codes:

0402 - Fuel tank temp. sensor
0803 - Absolute pressure sensor
0807 - EVAP Canister
0903 - EVAP Canister Vent Control Valve

None of these are important. 0803 is for the Auto tranny, and the rest is EGR-EVAP style crap that I dont care about. Im out of ideas. We still get the some pretty violent backfires (but not constant) but with either ECUs it REFUSES to start.

Can the knock sensor have anything to do with that? I unhooked the EVAP crap and the Knock sensor harness just so its exactly like it was when I had the VQ35 in it. For the heck of it. And it still wont start

 

The codes you get are from EVAP incompatiabilities between the electronic and canister setups. Mostly, 95 has canister EVAP and 96+ has electronic EVAP. So you are right, those codes really wouldn't affect the outcome of using either AT or MT ecu's. I think you are supposed to get 3 more codes for the transmission sensors for the AT ECU. But that's not important either.

Back to your problem... After you've redone your timing and it still wouldn't start, that really knocks my head out. I can tell you from my experience, though. When I was doing the JWT cams on my 3.0 setup, I installed it twice and none of which can start the car. The third time I did the timing alignments, it worked, but only for a couple weeks, the cams snapped on me. I later found out on that motor that the heads are warped. So that's why I wouldn't recommend people to open up the valve and timing assembly to mess with timing. To me, these VQ's timing assembly is black magic. It's crossing fingers and praying that got it to work. I swear I've aligned it all to perfect specs on those installs, but they turned out faulty mysteriously. Now, another thing to do with timing install was to rotate it manually after the perfect alignment. It make take up to 20 rotations to correctly confirm that timing is lined up perfect. That's what I've learned from experience.

On my 3.5 setup, Stephen Max built my hybrid pathy+maxima motor. The first time we put the engine in, car almost couldnt' start, it's got timing problems. cylinders 1 and 2 wouldn't fire. Then we took out the timing assembly and found it off by 2 teeth. It's perfectly aligned from Stephen, but mysteriously, like black magic, it became off upon cranking. We then did the alignment again and it sputtered at lower rpms after starting. Very bad and rough motor. Then we found timing to be off somewhat half a teeth like. Aligned it again and we have it perfect on this third try.

The conclusion from my end is that timing is very hard to deal with on both my 3.0 and 3.5 VQ's. I dont' want to resort your problem back to timing again, but it may very well be.

Now, can you do the following for me?
Go to your motor, take out the 1st ignition coilpack, leaving the spark plug in it. Use a spare sparkplug and attach it to the 1st coilpack. Get people to try to crank it, check while it's turning to see if there are sparks. The procede to do all the ignitions one at a time to see if you at least get sparks. If you do get sparks, most likely, you've got the timing right. That was what I did to finally get everything right at the end.

-Peter-

 

Well we get sparks, but its wierd. The middle cylinder on the rear head, and the cylinder closest to the drivers side on the front head - BOTH shoot way too much spark, and the rest of the cylinders do not, they only throw an erratic, once-in-a-while spark. We interchanged coil packs several times, and it doesnt change anything, the same 2 cylinders get too much spark. So the coil packs must be fine. I guess I could try with both ECUs to see if this changes, but the car acts EXACTLY the same with both ECUs.

Edit: Now I get idle speed code 0205.

This crap, I swear

 

Yeah, this idle speed code must have come from erratic rpms due to the spark problems. From your spark summary, I still think your timing is faulty. I know you've changed your crank and cam sensors. Can you resort back to the 95 OEM sensors? You're currently using DEK sensors, right? I think the best approach is to back engineer to stock-ish setup to trouble-shoot outwards.

All this mess really caught my attention to timing assembly. I know you have crank POS faults. This could very well be your ticket to the ballgame.

Another to look at is the injectors. All the backfiring issues come from rough tunes from the ECU or rich mixtures in the exhaust, then this means your injectors probably stuck open and backfired in the rear alley. Do you have spare injectors on a rail to use? I had that problem before too, and changing out the whole rail got my problem fixed.

-Peter-

 

0805 - Absolute Pressure Sensor

These are only found on Automatic transmission vehicles?

"The sensor detects ambient barometric pressure and intake manifold pressure respectively, and modifies the voltage signal received from the ECM" --FSM

I thought it was just IM crap. Oh well ... another strike to add on my excel spreadsheet.

 

Well I pulled out the original harness and did one from scratch DIY like I had done for the 240 and put extra care into the shielded harness for the Crank and Cam sensors. Now we still have the same problem, but the spark is stronger yet still erratic. So I guess that confirms I would have been able to start the car if we didnt have that problem (and thus doing the same for the S13 would have started that VQ35 a long time ago - oh well) but it still completely refuses to start (although it seems to be trying harder now).

We have a brand new Crank POS and Cam sensor on with a 100% fine 5-speed ECU. Voltage to the coils and injectors is 100% normal, too. If all else fails I will tear the timing equipment back down to verify, but we aint there yet.

 

I dont know man. Your car would backfire while starting but it would still start, right? Its true that he put about 10-11k miles on this car with the starting problems and backfiring so after a while it might add up, but when it ran, it ran fine. And that still wont explain the erratic timing.

One more thing. With either the original wiring harness or my DIY wiring harness, the SAME two cylinders have random spark (front bank, cylinder 6, and rear bank, middle cylinder). Same thing, except somewhat stronger sparks. The fuel rail has NOTHING to do with what sort of timing the ECU sends to the coils.

And finally, can someone tell me how the timing being off by a tooth or two could cause the SAME two coils to fire and the 4 others to not get anything at all? As far as I know, when I first opened up the timing assembly, all was aligned just fine and now, the car acts exactly the same, only the sparks are somewhat clearer.

 

Teared off the timing assembly again (im getting pretty good at this, about an hour to take Alternator, pulley, PS, passenger side motor mount and timing cover off with the motor in the car). And it looks like the timing is still spot on. So theres nothing wrong with the timing assembly.

Im all for changing the whole fuel rail (because of the backfires) but how could this possibly have anything to do with timing?

 

My experience with backfires are either from off timing or fuel richness due to foul injectors.

Timing being off will throw codes most of the time, in your case, it's really not so. Though I tried to talk you into checking the timing assembly over and over, your latest diagnose confirms it's not timing. I am sorry to have made you overwork yourself on that case.

When my injectors were bad: stuck open and/or partially stuck open, it had never thrown any codes at all. I remember that it would be rough at idle, a little skippy and some backfires, that's about it, and reving towards about 3500 rpms and beyond it would drive fine and smooth. But starting the car wasn't a problem, though. It may not start only sometimes, but I'd never called that my symptom of the problem. Your case sounds a lot like an injector problem. I didn't even bother replacing each individual injectr, I just went and got a set on the rail and replaced them. Then there's no problems at all.

Answer your question about cylinder firing due to timing off by tooth or two. The cam sensors will sense the magnetic link that signals the 1st cylinder to fire, then the rest follows in a sequential order accordingly. When your crank sensors (ref and pos) are working correctly, indicating the correct positions of your pistons, it's all good. But while your crank sensors are good, and if your timing is off by 1 or 2 teeth, the cam sensor will read the link a little ahead or a little behind depending on how much it's off. The combination of the crank and cam sensors in this case will cause wrong firing times because your pistons are moving up and down normally, but your cam sensors are off, making the ecu fire at the wrong times. The interpretation of the ecu to fire ignition signals are very precise, and off-ing by a tooth or two amplifies the metrics several degrees off, making it critical and may overlap the firing sequence and thus you can see "maybe" 2 cylinders firing more and 2 cylinders not firing at all depending on how much timing is off and where the signals are overlapped. I know this is a raw explanation, but that's how I would "say" it in english.

-Peter-

 

I understand the relation between the crank REF and cam sensor perfectly. But how do the injectors relate to erratic spark...

 

injectors squirt accordingly prior to each ignition signal. If your ignition timing is messed up, correspondingly, your injector pulses will do the same.

However, if your injectors alone are messed up, such as stuck open, ignition timing will stay normal and spark in the same order it was supposed to, except in this case that your injectors will keep squirting fuel even when they're supposed to be closed.

So you've just brought up a good point, since your sparks are out of order, sure your injectors are squirting out of whack, then we cannot for sure say that your injectors are the key to this problem. So I'm all out of opinions to share at this point. Sorry. Your problem is extremely odd to me, and truly, me done a few cam jobs and a few motor rebuilds with Nick doesn't put me in the right ground to lecture you on this. I can say that I'm learning as I go. I hope someone else can chime in on this here. I'd like to know what's going on, too.

-Peter-

 

Is the TPS adjusted properly? If it isn't it can definitely keep the car from starting.

 

did you say you checked the reluctor ring? is there any way you could datalog CPS signal? then you would at least know that the ecu is getting the right spark pattern.

 

Really - well I unplugged my TPS once and it still started. Unless you mean only in the event that its plugged but not well adjusted. So the TPS can screw with the timing? What about the MAF, can it screw with the timing too?

 

Well I just found out the TPS ground wire was completely cut so when it was running it was running as if it did not have a TPS at all. I am re-doing the TPS, MAF and coolant temp sensor wiring all at the same time. Not sure what this is going to yield.

 

This could definitely solve the entire problem. I can't wait to hear the results.

... been following this thread way too long.

 

Nope. Perfectly re-did the MAF and TPS harnesses (shielded harnesses with extra care to the grounds that shield the harness) and coolant temp sensor wires. Still backfires randomly and still wont start. I really need the weekend off on this one.

 

Check the TPS resistance next if you haven't already done that. Should be ~500 ohms at closed throttle and ~4000 ohms at WOT.

 

You really think it has something to do with the TPS huh? I will check that, and I have another TPS for my 240 that I will swap with. It is a 2-plug (WOT switch) model though, from a 95 auto.

 

:attention

 

Yes that was checked, double checked and triple checked (im not kidding!) with a mirror and the teeth on the flywheel are all perfectly aligned. Same with the 4 teeth on the crank pulley and theres nothing wrong with the signal bumps on the cam sprocket for the cam sensor. It seems nothing is wrong with the engine physically (when it runs, it runs perfectly).

By the way, is the resistance the same for both TPS models? Meaning the model with one plug and the model with the WOT switch?

 

Update: Checked the voltage directly at the ECU pins for the 3 crank-cam sensors:

Crank POS: Roughly 2.5V while cranking.

Crank REF (Pulley): 0.3-0.4V while cranking.

Cam Sensor: 0.1-0.2V while cranking.

So the Crank POS seems in spec, but not the other two. If the resistance STILL checks fine on the Crank REF and Cam sensor Ill buy shielded harnesses and re-do these again. It seems the ECU is really picky for those dam signals.

 

I assume you are using either an analog or digital voltmeter.

You cannot accurately measure a pulse type signal with either of those. An analog meter might bounce at a regular interval for you, depending upon the damping, but the reading will be meaningless.

What was the point of this thread?

http://forums.maxima.org/showthread.php?t=509114

 

But the 2.5V reading corresponds for the crank. I wasnt looking to get an exact reading but rather be sure that its at least getting something.

The point of that earlier thread was to get an exact reading. I used the multimeter just to confirm that either sensors were actually sending something to the ECU. I know its not the correct tool for the job though.

We have to take the car out for a few jobs and we are getting a deal on a 95 auto max in several weeks (400$ for the car, has 380,000 KMs on it) so when we get that one we'll test 100% first hand what sensors need to be detected and what sensors dont, there is way too much speculation going on about which sensors are necessary and whatnot. We'll have plenty of spare sensors to swap with.

 

It has to do with time. The A32 flywheel signal plate creates a signal that changes from high to low and back every 1 degree of rotation. That results in a pulse type signal with a 50% on time. The sensor has 5V supplied to it so the average sensor output voltage is 2.5. The signal changes so fast that your meter only displays the average.

Your other two sensors output a signal that is "off" or negative more than it is "on" so your meter reads a much lower voltage.

Did you try putting your meter on AC volts?

 

I tried all 3 types of volts.