Hey,
I've put a VQ30 into my 1995 240sx and need some help getting her to run! I've got everything wired up and it cranks just fine but won't fire at all. I have power to the MAF, rear crank POS sensor, all injectors, all coil packs and the TPS. The injectors aren't firing and neither are the coil packs and I can't figure out why, any ideas?

I tested to make sure the harness wasn't damaged on the injector wires that go to the ECU and they are fine. The engine is grounded and so is the wiring harness at the intake manifold.

Does anyone know what would make a VQ not fire with power to all these sensors?

PS. I'm using a 98 VQ and a harness and computer from a 95.

thanks for any help
allen

 

You need the CAM sensor that goes on the timing cover. Check the ECU codes, look at the 4th gen stickies if you do not know how to. Also you need the CRANK REF sensor on the oil pan near the pullies, it is VERY important(as is CAM).

 

I've got the cam sensor plugged in but it doesn't appear to have any power to it with the key on - looking at the FSM it doesn't appear to get any power from the ignition like everything else does.

The front crank pos sensor is not plugged in but I didn't think that would keep it from firing.

Thanks for the ideas, I'll try the front crank sensor for sure.

aleln

 

Both cam and crank (pulley) sensors are magnetic pickups, they won't have any power going to them. They generate a signal as the metal teeth pass thru their magnetic fields. The POS crank sensor by the flywheel has a voltage pickup, but operates in a similar manner.

I would check your ECU for codes if you can and get back to us on the ones it spits out. To me it sounds like a bad cam sensor or it's wiring because the car will start and run without the crank (REF) plugged in, but it will crank and not start if the cam signal is not getting to the ECU. Or it could be something else in your setup.

 

I'm gonna wire up the GST plug so I can use a scanner I borrowed. Hopefully it will tell me something.

I'll report back w/ my results soon.

allen

 

Ok, got the GST port wired up and ran the scan here's the codes:

0180 - fuel pump sensor

0105 - map/baro circuit

0443 - evap purge valve

0446 - evap vent circuit

So, I'd call that a bummer. None of those seem too important. I've got the front crank pos sensor plugged in but not mounted up (have to make a custom mount because of the oil pan I'm using) but it didn't give me any error for that. And, no error for the cam pos. sensor like I expected. I'm really stuck now.

I noticed the ECU gets pretty darn hot when the key is on but maybe it's supposed to, not too hot to touch but very warm.

Any tips or ideas?

thanks
allen

 

Hmm, maybesome thing is touching? Are you 100% positive the grounds are good?

 

I was about to suggest the same thing. Make sure the harness grounds are solid.

 

Well, I bolted down the two black grounds that bolt to the LH side of the intake manifold and I grounded the engine to the frame, I'll go over it again to make sure though.

Next I'm going to redo all of my connections, I've had to integrate the 240sx dash wiring into the VQ harness to get ignition power to the right places so maybe I've got something mixed up there. I'm beginning to suspect the ECU itself though since all the sensors, etc., do have the power they need. It's as though the ECU just isn't doing it's job, it appears to have all the signals it needs to fire but just isn't doing it.

I also swapped the cam sensor w/ another one and that didn't help.

thanks,
allen

 

I know a few people, including myself, that had no start problems due to grounds. We all thought they were good but they were not, so I made a WalMart ground kit and grounded those 2 main grounds on the IM to the BATT and regrounded hte batt.

 

Hey, you just made me think of something! I don't think I've got those two intake manifold brackets that brace the IM to the head bolted on. Without those I don't think the wiring harness can find ground anywhere because of that rubber gasket between the upper and lower IM.....as soon as it stops raining I'm gonna ground the crap out of that sucker and she what she does.

thanks
allen

Now that I think it through it should ground through the IM bolts but, oh well, I'll still give it a shot.

 

That is what I thought too

 

Ok, grounded the harness grounds straight to the spot that I have the engine grounded to but it didn't make any difference. Still cranks like crazy but wont catch at all. I'm really getting discouraged now, i'll go over all my connections tomorrow.

allen

 

If I unplug my crank or cam sensor and try to start it should the code reader show an error code? That would verify that the ECU is even seeing those sensors right?

allen

 

Yes.

There still is no spark?

 

Well, I didn't actually pull a plug last night to verify that but, it sure didn't sound like anything was happening. Tonight I'll pull a plug and crank it to see if there's some spark or not.

allen

 

It might be a fuel issue for all we know.

 

Well, I don't suspect a fuel pressure/pump issue as I can hear the pump prime. However, I don't think the injectors are opening because of the lack of fuel smell on the plugs the last time I pulled them. Anyway, I've got a fuel pressure guage, I'll do some more testing tonight then get back w/ ya.

allen

 

Stick a screwdriver or something on one of the injectors, they tick loud enough so you could hear them when you have someone crank the car.. We did this when I installed new injectors to make sure they were working :-x

 

Thanks for the idea, I'll try that. So, they click loud enough to be heard over all the cranking noise?

allen

 

Our injectors are pretty loud.

 

No, not while cranking. But you'll be able to hear it if you stick a screwdriver on it and hold the blunt end to your ear.

 

Gotcha, thanks.

allen

 

Do you have the rear crank sensor hooked up ? Its the one that reads off the flywheel, if you do not have that the car will not fire up at all and it will also NOT give you any codes. When I did the 1st 6spd swap this didn't pop into my head as to why the engine would not wanna fire, then after thinking it over I messed with my 5spd Max and it wouldn't trip a CEL and wouldn't fire. I had to take the tranny out of that Max, send the flywheel out to get it machined for the right CKP tooth pattern. Since the engine is looking for voltage generated by the crank and cam sensors it will not display a code if the sensor is not plugged in durring start up. I think you have a crank/cam sensor problem. If you unplug the cam sensor while runing the engine, it should still run but thats when it will trip a CEL. It sees that the crank is sending signal and the cam isn't and it will throw a cam sensor circuit failure. Good luck and let us know how it works out.

 

wow its like a cliffhanger. more props to ya man, and when u get a chance post a pic of the convo! good luck man... +1

 

I'd rather fall off a cliff than be a part of this cliffhanger!

Ok, so I tested a few things. First I did a continuity test of the cam sensor, TPS, and MAF wires just to make sure there wasn't a broken wire in the harness going to the ECU and it all checked out ok.

Next I started to hook up a fuel pressure guage to prove I have fuel pressure and the large stream of fuel that hit me nearly in the face told me all I needed to know, pleny of fuel pressure, pump is working fine.

Then, I checked for power at the ECU plug w/ the key on but the ECU unplugged. Got power to pin 24 but not to the other's that should have it (67,72,80 and another or two I think)nor at the crank sensor, cam sensor, TPS or MAF plugs. Got worried, plugged the ECU back in and then power was restored at those sensor plugs just fine, strange I thought, oh well at least the sensors do have power when all is plugged in and the key is on.

Next up, I uplugged the rear crank sensor and cranked it over a few times but the code reader still shows the same 4 codes as before.

Then, I did the same to the cam sensor, still no new codes.

Finally I pulled a plug, no fuel smell and no arcing to the valve cover while cranking so still no fuel or spark.

I too believe I have a cam or crank sensor problem but I'm not sure what to do next to prove it. I'm using a 4th gen flywheel, ecu and sensor. I had to grind the oil pan down and in to make the sensor line up w/ the ring gear but I feel that I got it aligned correctly, maybe ever so slightly off but not much. If it wasn't aligned your saying that I would get no codes at all?

Lastly, for some reason I can't clear my codes, the code reader says it's clearing them then it will say "3 codes remain", I'll try to clear them and it will say "clearing 4 codes", clear them then say" 3 codes remain, over and over again.

allen

 

One time when I did my first Y-pipe install I unbolted that crank sensor for the flywheel cause I was changing the o2 sensors. On assembly I didn't align that sensor just right and the car had similar symptoms as yours does. Except we had fuel injectors spraying but no spark. The alignment of those crank/cam sensors is critcial, also I believe anything that's effected by a magnetic field (Ex. iron, some types of steel) that's close to that sensor throws off the readings.

 

I'm not disagreeing with those saying crank/cam sensors but did you verify the injectors are working? Even with fuel pressure if you have an electrical problem and they're not opening...

You did say you didn't have any fuel smell the last time you pulled the plugs...?

 

Correct, no fuel smell.

I guess tonight I'll try to hook my mulitmeter up to the crank sensor and spin the motor. If the meter pulses then the sensor should be close enough to the flywheel ring gear, if not then I'm in for some work.

allen

 

Are you getting any intake backfires when you try to crank?

And just for clarification, you will get spark and the injectors will spray even if there's a fault with the CPS (POS). The timing, however, will be so erratic and random that the car won't start.

Edit: This is the case only if there is a weak signal coming from the CPS, from either a faulty sensor or it being too far from the timing ring. This won't hold true if it's removed altogether, of course.

 

No, I'm not getting any backfires at all.

Well, I'm really lost then. I'll try to test the sensor anyway just to see what happens. I wonder how far from stock the sensor element would have to be to not get a reading at all.

Anybody know what the condenser does? I've seen it in the wiring diagrams and wondered what it actually did and if it could be at fault for any of this.


allen

 

Could you have a Bad ECU?

 

i was thinking that too. it all seems to add up but some variables just dont make sense. all leads back to ECU. however the injectors not firing seems to be most of the problem, but WHY are they not firing.. or is that basically the last 7.2 posts reworded for dummies?

 

Well, I attempted to test the rear crank sensor for signal using my multimeter but failed miserably. Anybody know how to test one of these things? I couldn't figure out prongs to test on the sensor or what setting to put the multimeter on.

However, I did take another look at the hole I enlarged in the oil pan for the crank sensor. Although I can't SEE the flywheel/sensor clearance I did notice that the sensor will hange in place w/ no bolt just on magnetic pull alone. I think the sensor is close enough to the flywheel to get a signal.

I'm in the middle of extending and soldering all of my connections, once that's wrapped up I'm going to try a different ECU I guess.

allen

 

Any chance this could be somehow related to using an automatic ECU w/ a manual tranny?

allen

 

No, you would just get a bunch of CEL but it should still run.

 

The procedure as to how to test the CPS (POS) is a little more involved than with other sensors. Do you have the haynes manual or FSM?

 

I have an FSM that I downloaded.

allen

 

Check the EC section, it says how to test all the sensors.

 

Found it, EC-196 for anyone else looking. I'll test tonight.

allen