1995 j30 hesitation problems

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mej30guy
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Good morning gang!

I finally made to the board! Here's my problem.

I have a j30 that looks like it just came out of the showroom. New timimg belt, fuel filter, tuneup, etc at 122k. (now has 140k) New EGR this past June. Cleaned out the engine and injectors with MOC1 last week. (surprised the EPA didn't pay me a visit)

Friday night I cleaned the MAF sensor after reading directions on this site. DO NOT use brake cleaner, as one poster said you could. New squirt of MAF sensor cleaner fixed that mess.

For the past year or so, when I accelerate from a stop, sometimes the engine will bog down with low rpms and no power. It catches up eventually. (makes pulling out into traffic a bit of an adventure) High end, it runs like a top. 75-85mph without so much as a belch. Checked the fuses, and found that the 10a injector fuse was missing. Replaced that, without improved results. Did the self AT test with the blinking lights, and it passed with flying colors. Manually went through all the gears, and it shifts like it should.

Sometime when I step on it on the highway, the engine is slow to respond. If I gradually increase speed, it's fine. I'd like the lagging from a stop to go away. Any thoughts? It seems like you guys are my best source for an answer. If you need any more info or symptoms, let me know.


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yodawill2000
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Need t check the ECU for a Knock sensor code.It will not trigger the check engine light.A "How too" is a stickie in this forum.

If it bogs till about 3k then kicks in as normal that would be my first guess.

mej30guy
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not out of the realm of possibility because the sensor was disconnected about 2 years ago due to the cost of replacement. ($600) my mechanic is a former dealership lead infiniti mechanic with his own shop. he said that the sensor is a piece of cake, it's just impossible to get at.

Can I get him to do a relocation without a removal? I've seen that option on here plenty of times. Can I do this myself? The experts on here say it's a 10 minute fix. I certainly hope so.

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Infinitiguy19
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1994 Infiniti Q45a 240000 Miles

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What about the fuel filter, when was that changed?

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yodawill2000
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If your KS is disconnected that's the problem.Your engine timing is retarded big time, By design.To relocate you will need a knock sensor AND the cable harness.Then there's no need to remove the old assy.The original Knock sensor is on the block below BOTH plenums. Major task to get too. Just ask Scott.


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gr8scott72
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yodawill2000 wrote:If your KS is disconnected that's the problem.Your engine timing is retarded big time, By design.To relocate you will need a knock sensor AND the cable harness.Then there's no need to remove the old assy.The original Knock sensor is on the block below BOTH plenums. Major task to get too. Just ask Scott.
Yes, you have 3 choices. Well, I guess you have 4.

1. Do nothing and continue to have crappy performance.

2. Bypass the KS with a resistor (search site for size) tricking the ECU into thinking the KS is working as it is supposed to. (Must ALWAYS use 93 octane gas after this.)

3. Replace the KS. This is the reason that your mechanic unhooked it. It's MANY hours of labor. The upper AND lower intake manifold plenums have to come off. You could probably change your timing belt in less time than this would take.

4. Relocate the KS. It won't be quite as effective as it is in the stock location, but at least it will be there to pick up some knock. You can find the knock sensor on ebay for about $60 or pay Joe at everythinginfiniti.com about $100 for a NGK KS. You will also need the wiring harness which I found at my local Infiniti dealer for about $20.

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gr8scott72
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ppastos wrote:What about the fuel filter, when was that changed?
Reread his first post. You'll find the answer.

mej30guy
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The KS was kind of what I was afraid of. What kind of job for a mechanic is it to relocate the sensor? From what I've read, it takes you guys minutes, so it shouldn't be more than an hour of labor plus parts.

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yodawill2000
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Thats correct.Here's a How too.Be aware the 300zx had the same engine.

http://www.angelfire.com/geek/....html


mej30guy
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If I go the bypass route, can I burn 91? It's all I can find around here.

Which method is easier?

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yodawill2000
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Obviously the resistor bypass is easiest, but if the engine does knock it could be a very expensive problem.

mej30guy
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I guess the easiest way to attack this, is to know what I'm attacking. I'll wait to see what codes come up when I check the ECU.

Would a faulty MAF sensor cause this to happen as well? I cleaned it with the proper stuff on Saturday, and it ran like a top at the high end. The lag happened before the cleaning, too. (I did noticed that I badly need an alignment) But the high end was never a problem, it was always the low end lag.
Modified by mej30guy at 12:40 PM 9/15/2008

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yodawill2000
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The Knock sensor is ignored above 3500 RPM.

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gr8scott72
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mej30guy wrote:I guess the easiest way to attack this, is to know what I'm attacking. I'll wait to see what codes come up when I check the ECU.

Would a faulty MAF sensor cause this to happen as well? I cleaned it with the proper stuff on Saturday, and it ran like a top at the high end. The lag happened before the cleaning, too. (I did noticed that I badly need an alignment) But the high end was never a problem, it was always the low end lag.
If you know that your KS is unplugged, there is no need to look any further. THAT is your problem.

Don't pay someone else to relocate it. It really won't take that long. The hardest part would be just finding the connector for the KS harness.

mej30guy
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Last night my wife drove home from work, (why not it's her car) while I watched the speedo and the tach like a hawk. When accelerating, the engine revved fine, but it seems like the tran doesn't catch up. On other occasions, both the tran and the engine lag. (fuel flow roblem?) Could some cylinders not be firing the way they should.

At one point, we came to a stop sign, turned right, and proceeded up a slight incline. The mph never got above 15 while the tach hit 3500, with the engine screaming. Eventually, the tran caught up with the engine. My thought is, the engine was getting plenty of juice at this point, so no fuel flow issue. With the rpms that high, we should be going faster than 15mph.

When driving on a flat road, the engine seems to be revving very high before the tran shifts. A lot like driving a standard, and shifting late.

I really don't want to chase this around and replace part after part. I'd like to nail it once and for all. If the symptoms were more consistent, then it might be easier to diagnose. I'm an exterior guy, not an under the hood guy, so it's a little hard for me to verbalize. That's why I'm relying on you guys for help.

One mechanic told me it's the ks, while another tells me the ks has nothing to do with the engine getting fuel. It only picks up noise in the engine, sends a signal to calm it down, and is the biggest rip off in the auto repair industry.

HELP!!!

By the way, my dark green pearl looks as good as Scott's rig. It's a head-turner!


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gr8scott72
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mej30guy wrote:Could some cylinders not be firing the way they should.
All of them are not firing like they are suppose to be. The engine thinks you have crappy gas in there and that it is pinging/knocking like crazy. (Due to the KS being unplugged.) It retards the timing SEVERELY to keep the engine from knocking and self-destructing. The amount that it retards the timing is enuf that you not only feel a decrease in performance but actually think something is wrong with the engine.

Just go stick a resistor in the connector and see if the problem goes away. I bet it does.

mej30guy
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I don't think I could have received a better response. Thanks for the explanation. Now everything makes perfect sense.

Where do I go to find out how and where to hook up a resistor to bypass the ks before I get a new one?

mej30guy
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I just read a "how-to" to go the resistor route. I didn't realize that it's basically a permanent fix. I'll opt for the re-routed ks instead.

Is the ks connector the red one that sits at the top middle of the engine, just in front of the firewall? I don't want to disconnect the EGR by mistake.

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gr8scott72
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mej30guy wrote:I just read a "how-to" to go the resistor route. I didn't realize that it's basically a permanent fix. I'll opt for the re-routed ks instead.

Is the ks connector the red one that sits at the top middle of the engine, just in front of the firewall? I don't want to disconnect the EGR by mistake.
It's not a permanent fix. All you have to do is take the resistor back out. Relocated is better but you might want to try the resistor first.

From your description, you should just be looking for the unhooked connector. I don't actually remember which one it is. You'll have to search more on here or just wait til someone else answers.

GerryO
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On my '93:

The connectors for the two O2 sensors (one on each side of the engine) should be the same size, shape and color as that for the KS. Their wires are sheathed in a white protective material and connect pairs of black and white wires.

The two wires leading from the temperature sensor on the EGR tube (CA only?) are much smaller in diameter and sleeved for protection. Other than those two wires the EGR valve connections are all metal and rubber tubing.

The two KS wires are the same size as those of the 02 sensor, but are different colors and wrapped together in black. The run up from the rear center of the engine from beneath the plenum and the intake manifold.

Ideally you'll need to purchase a new harness piece to connect a new/relocated KS to the ECM harness connector.

I'd send you a photo, but all of my connectors may not be in their original positions, after doing my plenum pull. My unconnected KS wires might be visible a few of the photos that I posted in late June of this year, but you are looking for the KS to ECM harness connector.

Also consider that your TPS could be set incorrectly, as after I'd first reassembled things after my plenum pull, I'd connected the KS to one of the O2 sensor connections and vice-versa and I'd adjusted the TPS to the point that the car ran fairly well (with the TPS compensating for the otherwise delayed shift points caused by the missing KS input).

What's your idle rpm speed when in D, with your foot on the brake at a full stop and when the engine is fully warmed up?
Modified by GerryO at 8:53 AM 9/17/2008

mej30guy
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Well, I crawled all over the engine last night and couldn't locate where the knock sensor was disconnected. No wonder it costs a pile to have these things fixed, you can't get to anything! I thought I had found the ks twice, but figured that they were the O2 sensors due to their shape and location. My guess is, that the passenger's side of the engine is my best bet, because it's a little more "spacious".

I never removed the plastic engine cover, so it might be somewhere under that. I spotted the 2 bolts on the top of the engine where the replacement ks will be located, so I knew I was in the right area. I had the EGR replaced in June, so I'm sure the ks connection is somewhere near that.

Am I looking for a connector with nothing coming out of it? Those should be easy to spot, I would think.

RPMs at a stop are somewhere in the 1-1.2 area and quiet as a morgue.

Ebbtide
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zerothread?id=282494

"for those who are wondering where the kS connector is, look at the picture posted by jertapper. the one with the red circle. If you look directly to the bottom of the picture you will see another connector, that is the KS connector."

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yodawill2000
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Thanks Ebbtide.

I thought I had that pic saved but couldn't find it.

GerryO
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mej30guy wrote:
Am I looking for a connector with nothing coming out of it? Those should be easy to spot, I would think.

RPMs at a stop are somewhere in the 1-1.2 area and quiet as a morgue.
If your KS is disconnected you should find the end of the sub-harness that's connected to the KS and the corresponding empty ECM harness connector where you'll connect your new/relocated KS.

Engine idle speed under the described conditions should be closer to 650 rpms, making it much easier to brake, better for gas mileage and is a possible sign of a TPS that's out of adjustment.

mej30guy
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Saw the pictures, and I realized that I was staring at that thing all night! I just didn't know what it was. Looks like a snap to replace. Mine looked like it was hooked up at that point, and not hanging. Maybe the ks was disconnected at a lower point deeper in the engine. If not, how would one disconnect the ks without unplugging it from the connection at the top of the engine?

Do you need to manufacture a special bolt, compression washer, etc.? I saw on another post that the guy machined out a new bolt because the stock one was too short.

The RPMs I gave you were for sitting in park, not in drive with foot on the brake. I'll get that reading later.

GerryO
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mej30guy wrote:Saw the pictures, and I realized that I was staring at that thing all night! I just didn't know what it was. Looks like a snap to replace. Mine looked like it was hooked up at that point, and not hanging. Maybe the ks was disconnected at a lower point deeper in the engine. If not, how would one disconnect the ks without unplugging it from the connection at the top of the engine?

Do you need to manufacture a special bolt, compression washer, etc.? I saw on another post that the guy machined out a new bolt because the stock one was too short.

The RPMs I gave you were for sitting in park, not in drive with foot on the brake. I'll get that reading later.
You can be reasonably certain that the other end of the sub-harness is still connected to the KS itself and I believe the connection at the actual sensor is one of those u-shaped wire type connectors.

You'll probably need to do some calling around to find a longer metric bolt with the same hardness rating and you'll want to tighten it to the specified torque number (over-tightened could be worse than under). Use the flat and split-type lock washers similar to those on the old bolt and maybe a bit of blue Loctite on the bolt threads.

Fully warmed up and in Park the engine rpm should be closer to 900?


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yodawill2000
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Mines dead on 750 with the AC off.Something adjusted wrong ?

GerryO
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yodawill2000 wrote:Mines dead on 750 with the AC off.Something adjusted wrong ?
In Park or in Drive with your foot on the brake?

Time to look at the manual, and it might be best to rely on something other than the instrument cluster tach.

And if you are happy with the rpm settings and the way the transmission is shifting, I wouldn't worry.

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yodawill2000
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In Drive.The Idle seems fine but as long as Ive had the J it seems to want to downshift too early under acceleration. As in speeding up for a pass and it shifts down 2 gears instead of one.It will go down to third, then zoom down to second.poor guy I'm passing thinks I'm showing off or something.
Modified by yodawill2000 at 1:05 PM 9/17/2008

mej30guy
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So it could be disconnected at some other point . I was just a little concerned that I didn't see one end just hanging there, not connected to anything, which even a dope like me could have figgered out.


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