poorcollegeboy

this is a long thread but bare with me since it a shot at solving a problem that so many of us have....

i know many people here experience the "engine heat soak" problem. i also know that many have replaced thier knock sensors and (re)gained some low end umph. maxima engines tend to be somewhat noisy as they get old. combine this with an old (sensitive) knock sensor that works off of piezoelectricity and you can have a very sluggish car. heat plays a role in any engine's performace, but it shouldn't effect an engine THAT much as all the people with the heat soak problem are experiencing.

i had this problem with my auto and i guesstimate that i loss around 5-10 hp on the butt dyno... at NORMAL operating temperature. i'm an advocate of those who belive that this problem is caused directly by by timing (i think rosenken and eric93se - gurus of knocks sensors and vtcs.)

as the knock sensors get warmed up, they start to fail or get too sensitive and give false readings (i.e. sensing all the wonderful noises that our 10 year old car makes as detonation) sending the ecm a higher voltage and hence retard the timing in our cars making it sluggish.

i'm going to try to eliminate this sensor completely. my plan is pretty simple - i'm going to fool the ecm by sending it a constant voltage. by looking at the wiring diagram, the knock sensor is directly linked to the ecm and doesn't mingle with any other parts.
i haven't had a chance to dig into the ve engine and actually see it, but just thought i'd throw this on the table and see if any of you experienced guys have an suggestion or comments. thanks for reading.

Mizeree_X

iTrader: (9)

Sounds reasonable if you can accept the fact that now you run the risk of damaging the engine if real knocking occurs (bad batch of gas or something). Keep us updated.

Agamemnon

At the very least, though, if it solves the problem (no more heat soak), this would confirm if the knock sensor really is the source of the problem. So, as previous poster said: keep us updated! And listen carefully for any pinging!

Aaron92SE

iTrader: (128)

Didn't some people already change their knock sensor and the problem wasn't solved? I believe someone changed their VTCs with it too and no luck.

poorcollegeboy

maybe thier car was making noise and the knock sensor sensed it as detonation.

and yes i will be listening very carefully for pinging.

nubiannupe

iTrader: (9)

Just imagining the good (no heat soak problem), the bad (engine detonation), and the ugly (...look on your face when your engine goes KA-BLAM) of this proposition might be intriguing. I can't wait to see the results, bro. Good luck!

Aaron92SE

iTrader: (128)

I can only imagine what it might be like to drive my car around town and always know that it's running mid 15's. That would make it so much more fun to drive. But instead, I'm driving around town in a low 16's 1/4 mile car. Major difference! I HAVE to find out my problem.

mtcookson

iTrader: (2)

could someone explain the "engine heat soak" problem for me. I've never heard of this term before.

Aaron92SE

iTrader: (128)

It only applies to the VE engine. When the engine gets up to operating temperature, it gets noticably slower than when cool or cold.

JC93SE

I have just now attributed my low RPM surging under throttle to the knock sensor. It seems to come and go (mostly here). When all is right, it's a bat out of hell.

My understanding is that only one wire to the KS actually does anything. The service manual says that there should be continuity between the one wire and ground (although with a very high resistance). I did not check for voltage from the ECM, but don't think there is any. If you figure that the KS is basically a microphone (look up piezo), the ECM is looking for a signal and cuts timing if it get one. You probably DON'T want to send voltage to the ECU.

I disconnected the KS at its connector, and it "seems" to have cut the surging, but power is still down. I wonder if the anwser is to GROUND the pin in the plug so that the ECM gets continuity, but I'm not sure that full continuity is the right answer either. It's still an incomplete thought.

Rungi

Where is the knock sensor located?

Thanks!

RosenKen

What noises does your car make? Mine's as quiet as new now that I have new VTCs, new exhaust studs and a WSP y-pipe.

I don't know of a single person on the org with a VE who has changed their knock sensor recently.

When I changed my VTCs, I noticed a BIG improvement in power across the rev range, especially at the top end. Low end power stilled lacked though, so I increased my ignition timing and it helped. The timing *was* at a stock setting so since I went ahead and modified it by increasing it, I think there's a problem here, and the only thing yet that I haven't replaced in the ignition timing loop is the knock sensor. I will replace it sometime this month though. But my car is fast all the time now... just hoping for a bit more low end oomph. VE's don't have the greatest low end power though

Do a search for VTCs and my name and you'll find a bunch of info to read. This has all been discussed before if anybody doesn't know what we're talking about.

VE30DE

If you look at the HP range, you will notice that at low RPMS we only have 30-100 HPs. I know my knoch sensors are good and my VTC's are good, and i have a slight hesitation off the lind because of the heat in Arizona. My car has 136k mi on it and everything's good. If you experience lag in the beginning check your launch. I know if I don't get a good start from a light driving normal or racing, I get a crappy start. Just check how you drop the clutch.

Kaya

poorcollegeboy

i thought it was the other way around.... ???? j/k

like rosenken, i'm looking for a little more low end umph. my engine is fairly quiet with the exception of a small lifter knock. the problem that i'm addressing however is not about launching. it's about the "heat soak" problem which sets in after driving for a while.

jc93se: thanks for the input. i have not had the chance to start this yet but from what i read so far, there is a small voltage being sent to the ecm... maybe it's just normal engine noise that causes this. b4 anything though, i need to get specs for the knock sensor like it's sensitivity (input/output readings), the programming of the ecm, and how the two communicate with each other (how many degrees is timing retarded for how many volts is being sent from the ks.) if anybody knows the answers to these questions or any other useful information post em here! peace.

JC93SE

It's mounted on top of the block under the intake plenum and coolant pipe. You probably can't see it (or just bearly) until you take stuff apart.

JC93SE

Actually the VE has pretty good power down low... when every thing is working right. That's what the VTCs are for. When mine was "humming" it was ballsy down low... or at least above 1500. The bad knock sensor has killed my low end power.

What does your ECM say?

JC93SE

PCB: After reading a bit on knock sensors last night on the forum, I wonder if tricking the ECM is a good idea. I haven't read on the heat soak problem and will.

I'm pretty sure that my KS is my problem with low and mid range power at present. The ECM is giving me the code. I know what the engine felt like during the brief periods that everything worked right.

Thinking a little further, it looks like the KS is one of those long-term "maintenence items" like so many others on the VE. I think we just need to accept that, and replace them when they go bad or get flaky. Figuring out how to trick the ECM is probably not the way to go. Imagine trying to diagnose other problems down the road and not knowing how the trick affects everything else, or having multiple tricks in place

Knowing that your engine is running tip-top means "knowing" all the pieces are working properly (or testing them to see), not "thinking" that your trick(s) are covering properly for the pieces that don't.

Band-Aid fixes bite you in the *** way more often than not. There's just no better way than doing things the right way... and "knowing" that you did.

MILLENIUM MAX

Hey guys does anyone here think that an oil cooler would help atleast a bit in solving this problem? Also does anyone know the thread size of the oil filter attachment?

eric93SE

iTrader: (1)

OK here we go


So I recently removed and cleaned my KS, and I believe it is a part of one of our maintainace stickies. http://forums.maxima.org/showthread.php?threadid=128490

Yes, after cleaning the KS I had a big improvement in low end. For all of you that want to measure the resistance of the KS: A new one should measure a little less than half a mega ohm (0.45 million ohms). My bad KS measured 5 meg ohm, which is, as you can see 10 times higher that what its supposed to be. This increase in resistance has to do with the terminal on the KS being corroded (I have pics but need to scan them). I say terminal b/c even though there is a double connector going to the KS, only one is being used, BUT there are two wires inside the cable going to the KS, the purpose for this is sheilding the signal coming from the KS from engine noise (high voltage interference coming from the ignition system).

Then the body of the car is acting as the ground for the KS. So with that being said, it is very important to clean the rust off the mounting surface of the KS, this too is a source of resistance that goes through the KS. Well it is and it isn't, b/c the bolt that holds the KS to the engine block is also a ground connection, so its not just the mounting surface that is really that great of a factor. Why is there rust in the area of the KS? Well if you hose your engine down a large POOL of water fills right where the KS resides.

Poorcollegeboy, you DO NOT want to send a voltage to the ECU. A KS is a voltage source (yes), it uses a crystalographic contraction and expansion to create an output signal. When the engine knocks it then sends a signal to the ecu.

SOOOOOOOO, how can you go about by-passing the KS? Well I think its pretty simple. You would need to install a resistor in place of the KS. Since we already know the resistance of the KS (about 1/2 meg ohm). BUT, you must realize how it is wired in (simple really), the connector that is accesible (in front of the crank shaft positioning sensor) can be disconnected, then you would need to find which pin is actually being used by the KS (the other is just the sheilding and should not be used) and then the other end of the resistor should contact the body of the car (completing the loop). If I need to rewrite that let me know!

I think I should add a little discalimer: Where I cannot be responsible for anyone F-ing up there car hehe.

any questions?

So, by installing a resistor in place of the KS, there will never be the singal telling the computer that the engine is knocking (and no reason to retard the timming).

Rungi

Thanks JC. I take it I'll have to remove the intake to replace the sensor? Ew. heh

JC93SE

Well, I haven't looked at it closely enough yet, but yeah. I think I read elsewhere on the org that someone got to it with a universal and an extension... not sure. Looks like the coolant pipe would have to go at least, though. Anyone with the definite answer?

I was just thinkin' today that if I have to pull the intake plenum that I might as well do the rear VTC... which then means I might as well do both VTCs if I do one. Oy. Well, they gotta get done sometime.

RosenKen

I think it's the 4th gen they can get to it without removing the intake.

Rungi

I'd have to admit that at about 94k miles my SE runs good.
No VTC ticking knock on my DOHC. =)
Just that good ol VE low RPM no pickup with my AT.

If I'm going to take off my Intake to replace that knock sensor I may as well have work done to it...

eric93SE

iTrader: (1)

I hear it's an easy job on the 4th gens. But when I did mine I had to remove the intake plenum AND the lower intake manifold. I hear Courtesy Parts gives a good price on the lower intake manifold gaskets. Some advice that I could give would be to remove and clean all the injectors and replace ALL the seals on them. the injectors over time are known to leak through there lower o-ring seals. Beck/Arnley makes an awesome fuel injector tune up kit it comes with all the gaskets and o-rings (there are actually 4 or 5 seals per injector) it also comes with the TB gasket and the plenum gasket.

http://forums.maxima.org/showthread....ht=pintle+caps


I forgot to mention carparts.com has a great deal on the complete fuel injection tune up kit, it's around $50

VE30DE

OK....think about this..we have an all aluminum block, heads, intake, etc. As the car heats up beyond nominal range, things start to expand. Although you want all the components to be made of the same type of aluminum, you still get impurities. So, the final out come would be parts contracting and expanding at different rates which would cause a loss of power. Let's say that the pistons and piston rings expanded at different rates. This would cause a loss of some compression but not all thus leading us to a loss of HP.

What do you guys think?

Jeff92se

iTrader: (82)

We have an iron block and aluminum heads

JC93SE

Uh Oh. You mean that the engineers missed something THAT big? Oh Man, all engines are doomed, and life as we know it will cease to exist.
That contracting and expanding of parts causing loss of power wouldn't be blood rushing from one head to another would it?

Just funnin' ya.

VE30DE

Thanx JC93SE. Thanks for the information on the cast iron block. I thought that we had an aluminum block. Anyhow. I talk with a guy that works at a dealership here in AZ, and he said that he had no clue on what could be going on and he has never had to address this problem. Maybe I'll just pay the big bucks to take it to the dealership to have them fix it and figure it out so that way we can all know what the frick is really going on with our cars. Because i'm sure we all like to have 100% performence 100% of the time. Right? Anyhow....I'm going to bypass the thermal switch on my fans and hopefully upgrade to an all aluminum 2core, maybe even 3 core if i can fit it. Since the problem happens after we've been driving for a while, if we can keep it cooler maybe we can solve it. Give me some info fella's. I want to know what you guys think about something that simple.

JC93SE

Ummmm: that was Jeff92SE with the Iron block thing.

Look folks: I haven't read every post on this "heat soak issue" but what I have read make me wonder the following:

1: Have those who have this problem checked their ECMs for diagnostic codes? No? Why not? If you have... great, but I see little that says folks even check.

2: This "heat soak" thing sounds a LOT like the knock sensor issues we have with the VE (VG too maybe), which points me back to #1 above. Very few folks seem to have made the possible connection between the two, and the KS appears to be a common failure. Even if the code for the KS doesn't show up in the ECM, the KS should at least be tested... maybe both cold and hot.

Maybe I (and a few others) have missed other key posts, but that's just how it looks to me so far.

male

Don't take it to a dealer thinking they will fix it for sure ..TRUST ME..dealerships are often the MOst shady places. I made this mistake once..it cost me a bundle..and they didn't fix it!!

eric93SE

iTrader: (1)

The engine will run fine with a bad KS, They will loose a lot of low end and the engine will run hotter. As I have mentioned a dozen times before, there is a technical service bulliten for our KS (which was posted back in 1993) and it states there there is a problem with the cable going to the KS and it also says that if the cable is OK then it may be necessary to replace the ECU. Now from my own experience I have found out what they meant by 'bad cable' which is actually the connector directly on the KS corroding. You can very easily test the resistance on the sub-conector to ground for the KS. A good KS has 1/2 mega ohms of resistance, while my bad one had 5 mega ohms of resistance. All I had to do was clean the connector really well (of course the hard part is getting to the KS) and then after putting the connector back on I used some silicon rubber to seal the outside of it from air/water.

The ECU does not come up with a code, The California computer may though.

JC93SE

Depends on what you call "fine". Presently, with mine connected you can feel it alternately retarding and not retarding timing when I've got my foot in to it, and "dead spots" at various RPM. I disconnected mine to remove the surging, but it's still retarded. Loss of MPG either way.

My ECM gave me a code 34 (knock sensor circuit) when I checked it. A "34" won't give you a CEL, so you have to check the ECM to get it. It is one of 3 or 4 codes (5sp vs. auto) that won't show a CEL. I cleared it, and it came back immediately. The connector at the KS may very well be my problem... I get infinite resistance on my 2M meter so either it's the connector/harness or the KS itself... maybe both.

My point is: does anyone actually check their KS or the ECM first when they have this "heat soak problem", or do they just ***** about it and speculate wildly about what it "might be".

RosenKen

I've tried to be one of the leading authorities on this issue. When the "heat soak" theory to this problem first surfaced, I became skeptical right away. No way will a heat problem occur on these cars after a number of years, but didn't occur straight out of the factory door. It is not a mechanical problem, it is electric.

I've spent a good deal of money replacing and testing parts that I felt could be wrong. Everything that tested bad, I replaced. I have NEVER had a check engine light or any computer codes, and I have checked a few times. Here is a list of things that were bad:

VTCs- as evidenced by the clicking
Throttle Position Sensor- out of spec
Oxygen sensor- I didn't check but just replaced anyway, it was old enough (probably original)
Coolant Temp Sensor and the harness that connects to it- It was corroded in the connector so I replaced both the sensor and the harness (I had to cut out the olf one and splice in a new one)... those style connectors are prone to corrosion, the VTC solenoid connectors are similar.

I have also checked the MAF, ignition coils, knock sensor, and every other component that has to do with ignition timing. I then advanced my ignition timing and got better power, which leads me to believe that there's something wrong with the system. It was at stock specs before I advanced it, yet it would hesitate in lower rpms a bit. Advancing it fixed that somewhat. I believe a new knock sensor will fix this. I have posted about this many times before and there are many people who believe my research. The one thing I have not done yet is actually replace my knock sensor for lack of time and money. I will be getting to it within a month though.

One thing I haven't checked but will soon- I want to do a pin by pin check on my ECU just to make sure the VTCs are getting the right signals. I've read a few posts where people replaced their ECUs because of this problem and it restored a LOT of power.

JC93SE

Cool. At least you checked the ECM, and at least you checked the other components before replacing them instead of blindly throwing parts at a problem like others seem to do (excepting the O2, I agree, but it still would have been good to check anyway to see the difference... either by resistance check or by monitoring it in ECM diagnostics)

You've checked the KS, and you intend to replace it soon. What results did you get when you checked it?

Disclaimer: I don't know everything. If I had all the answers I'd give 'em (or charge for them). It's just that it seems a lot of obvious steps get skipped

eric93SE

iTrader: (1)

I checked my 02 sensor with the on-board diagnostics while running the engine and it showed to be working quite fine. But I replaced it anyway b/c I know they dont last more than 60k. I then got s 15% increase in MPG.


RosenKen, I wanted to know if your were checking the KS connector properly. Only one wire on the connector is actually used, the other is only sheilding. You need to check both connectors to ground, one of them will give you a very high resistance. Please try this and post your reading. I'm betting it will be several meg-ohms.

VE30DE

OK...I think I've figured out what our problem is. I've talked with some people from UTI and they speculate that it's our intake manifold. It makes pretty good sense too. If you take a look around when you go to the track next, you'll see people putting bags of ice on their intake manifolds to keep the temp down so they don't experience a loss of power. I'm testing this theory as we speak. I drove my car till it puked and now it's sitting iwth a bag of ice on the intake manifold. I will post back in about two hours with the results. Tell me what you think.

RosenKen

There ya go, just replace the bag of ice every 30 minutes and problem solved! Are you serious? We're talking everyday power here, power that was there when the car was new and power that should still be there. This is not a problem that has anything to do with the design aspects of the car (ie, aluminum heads or intake manifold which heats up). The problem is that these cars age, their various sensors go bad and screw up the car's fuel/air mixture and ignition timing. The sensors report normal parameters to the ECU so there is no Check Engine Light. These early OBD (OnBoard Diagnostic) systems were VERY simple and almost never trip a check engine light or store a code, only when something outright fails (which would probably cause a very rough running engine or a stall, etc). The newer OBD 2 systems like in 97+ years are much more sensitive to smaller problems which is what we're experiencing here. It's a sensor issure. What sensor or sensors have gone bad, well you'll have to figure that out for yourself.

So stop speculating such crazy ideas and buy a FSM, and then search for these answers.

Drag racers use ice on the tracks before a run to cool their intake air down just a bit more to squeeze an extra HP or two out of their engines. Don't dump ice on your engine, since it'll melt and run down into your cylinder valley, causing the knock sensor to corrode and bigno, more problems!

JC93SE

Ahhhhhhh. So now we're saying that the "heat soak problem" is really a symptom of a problem and not a separate problem itself. Finally... someone who will corroborate(sp?) my same assertions.

Basically, I think what we have learned in this thread is this:

1: "tricking the ECM" is not the right way to do things- it's just working around the problem and not solving it... but hey, we like to mod/tune our cars so consider it a mod. Just be aware of the consequences of what you've done, and that it's "not right". Work around a few more problems instead of fixing them and let's see what happens.:eek:

2: The "heat soak problem" really isn't one... it's just that some "thing" isn't working like it should and it becomes apparent when the engine warms up (i.e. ECM goes into "closed loop") and gets bad information from the "thing(s)" that aren't right, or other "things" don't do what the ECM tells them to.

3: If you want to fix something, you have to do the work to diagnose the problem or pay someone else- but as we've often seen we are probably better off ourselves. The FSM and/or a Haynes (except in our case of the VE) or Chiltons or a Popular Mechanics/AllData CD is a really good start.

VE30DE: While you're waiting for your FSB to come in, search for and print the TSBs for your year. It's interesting reading.

Unless there are pertinent constructive comments, we've probably run this thread into the ground. Start a new one.

VE30DE

has anyone tried wrapping their DIS wires to prevent heat from getting to them?

poorcollegeboy

ok, so i finally went out to radio shack and bought 447k ohm resistors...

i'm prolly going to start in the next couple of days especially after my diappointing dyno results this past weekend.

http://members.aol.com/quocamolie/maxdyno.jpg

the knock sensor bypass will only be a tentative band-aid solution to see if it's the cause of the "heat soak" problem and maybe even see if its the cause of my power loss shown in my dyno. i do have a lifter knock that you hear at around 3k, so i wonder if the KS is picking that up as detonation. i KNOW it's not detonation b/c i use 94 octane and have the timing back to stock (15 degrees).

i will eventually replace my KS along with injectors and vtc's (if needed). just need to get down to the bottom of everything b4 i tear things apart.