91 knock sensor tips?

[Eskimo91q45]

parts are coming in monday and i am replacing the Knock sensors on my 91 q just seeing if anyone has done this and has any tips or tricks for this job

[qship96]

Hope you got the $1,000+ hose/gasket kit, as there are about 35 hoses under the plenum that tend to be brittle and crack when you disturb them as you remove the intake to get to the knock sensors.Good time to also do the valve cover gaskets and spark plugs.Atempting to skip replacing all the hoses often results in numerous vacuum,coolant,and fuel leaks and removing the plenum a second,third time to correct.

[LEMHEAD16]

$1,000 is a bit steep if you are doing it yourself!

Take your time, take pictures so you don't forget how things go back together.

Did you order the Knock sensor harness as well as the sensors? It will likely need to be replaced it gets very brittle over time. Qship is right about doing the valve cover gaskets (RTV on your year motor) and spark plugs (don't cheap out go for the OE replacement NGK PFR5G-11) it doesn't add that much more in parts while you have everything apart and saves you the labor down the road.

Also while you have the plenum off I would send the injectors off to be cleaned and tested, or replace them with a new set (ebay has a decent deal on a set of 8 currently) The injectors are a known weak spot on high mileage VH motors.

Don't reuse the plenum o-rings, they are cheap and you don't want a leaking intake manifold.

Be very careful when removing the plenum because the rubber lines underneath do get very brittle with age. If you have the funds replace them all with OE parts, I have used non OE rubber hose in the past for some of them, but there are a couple that are short and make sharp bends that will never work with rubber hose.

Be prepared for the car to be down for a while, I've never been able to complete the job in a day, I always forget a part, a gasket, or find another issue that needs to be dealt with. I'm in the middle of doing an injector service right now, so I feel your pain.

took me about 4 hours to get to this point and this is my 4th time doing it.


I commonly forget to remove the lower IAC hose and FPR vacuum hoses on the back side of the engine when I think I am ready to pull them plenum off

Here is a ling to a detailed post of removal
http://q45.org/plenum.html

Happy wrenching!

[LEMHEAD16]

PS be very gentle with ALL electrical connections, they tend to crumble if you are too aggressive with them.

[Eskimo91q45]

lol whoa thats gonna be fun tomorrow i have not gotten the wiring harness mainly cuz i coulnt find it ive called a couple places and a dealership if they had one... and after this project im going to be doing the timing chain guides and replace the gaskets for the vavle covers idk ill keep you posted will be starting prroject in the morning thanks for the tips so.

[Eskimo91q45]

well quick update i got down to the knock sensors both sides where cracked down the middle i got new ones in and gonna throw t back to together prob tomorrow as i cut bout 10 hoses and need to get them and you guys are right ive never worked on something that had si many hoses and they are all brittle u think if i bring the cut hoses to a part store they will have it? theres one im worried about and thats the y shaped hose in the back that connects to the IAC any help to find them

[Eskimo91q45]

oh also as i was taking my egr off i noticed the lil rubber hose connecing the metal pipe to the egr was rotted right thur as i tolk off the bolts the thing fell cuz the hose was so rotted my quesgion is would this do anything to proformance? just a question these knock sensor slow it down enuff was wondering if this could be adding to the problem. and would 2 bad ks make the engine run 45* BTDC or is ecutalk not acurate.

[reyrey9350]

knock sensors adjust the timing thats what there for.can cause the cel to go on. im working on my 1991 q45 doing the drivers side head,bent valves.... it broke the chain.got it like that though.

[LEMHEAD16]

Parts stores will not have the molded hoses. They are a dealer items, some of them you can get away with using straight sections of vacuum hose, but be prepared to shell out some cash. Infiniti of Scottsdale parts department has decent prices on them (and all OEM parts for our cars.)

[silverQ]

Hello,
Just recently changed my knock sensors as well. Twice was sold fake parts on eBay but was refunded. The sensors read zero ohms with multimeter and weight was off; sawed one in half was full of a gypsum type material and no wires. Ended up getting mine locally at NAPA auto parts looked like Altrom brand for $25 each.

One can check them with a multimeter should read right around 550k ohms for good. With patience and a normal wrench one can get at both sensors without removing the water necks. My two larger vacuum lines from the upper intake to the valve covers were degraded so replaced with heater hose and elbows, some others with fuel hose making sure of no kinks. Blocked off the fast idle cam coolant lines, two small lines running to the throttle body. Since it has caused me way too much trouble in the past. Good to move any iffy injectors to the one passenger side firewall and two front most positions for easy replacement in the future.

Then cleaned all the connectors and double checked my ohm values at the harness plugs when done. Used vaseline when installing the injectors or there will probably be o-ring problems. Finally hooked up a fuel pressure gauge to be safe of no gas leaking by.

HowTo on knock sensors and injector values @ http://www.q45.org/ohminjectors.html

[Eskimo91q45]

okay so im gonna go ahead and check the ks i got im not putting it together yet i got them from ebay and gonna ohms test them and see but only reason i got off ebay the autozone wants 120$ for one of them and i still have yet to ohms test the injecters will do tomorrow and did u cut the iac y shaped hose and if u did howd u replace it thanks again

[Eskimo91q45]

ohmed injecters at harness and all where in range but 3, 5 , 2 the 3 and 5 wouldnt read on the volt meter the 2 read between 5-10 ohms so i tolk them off the injecter and it was the same thing so what does that mean for the ones that didnt read? does that mean i got 3 bad injecters it does miss fire but never had a check engine light on

[elwesso]

CEL usually wont come on. If they didnt read at all that means they're DEAD. On a 90-93, not uncommon to have 3-4 bad injectors but the car still runs OK.

[Eskimo91q45]

okay cuz all it seemed like it was running with a slight miss i just might keep it apart a lil longer and get the injecters done too

[LEMHEAD16]

If you cut the Y shaped hose for the IAC better call infiniti and get one of those ordered up too.

I may have an extra one in the shed, I'll check tomorrow.

[Eskimo91q45]

okay that be great cuz i dont even how to order them i got most of my hoses replaced but that one and looking for a different set of ks cuz i dont wanna take the change of those being fake parts and not work and have to do it again. im so sad the q has been down for bout a week now but i think if i get it back with new ks it will run alot better. thanks for all the help so far

[LEMHEAD16]

I didn't find a spare IAC hose, but I did find a KS harness that you can have if you pay the $5 in shipping. Send me a PM with your address and I'll give you my paypal.

Any other parts you are looking for? I have torn down a couple of VHs over the years and have lots of little stuff laying around.

PM user DRFTBLD and see if he has the hose you are looking for.

[Eskimo91q45]

PM sent

does anyone have a clue how much that hose cost and how do i go about getting one

[LEMHEAD16]

Call your local Infiniti dealer or infinitipartsusa.com and tell them you need the IAC hose.

[Eskimo91q45]

sweet they got to oreder it but they want 36 for the hose and anther 15 to ship it but least i found one now just got to get my ks at a reasonable price and i should be good to go

[maxnix]

KS should be at 550K - 570K. Must replace teh subharness also.

If you don't clean like mad and replace every failed component (look at the inside of the hoses), you will be back very soon.

[OwnerCS]

I recently purchased a Standard Motor Products KS for the 99 Maxima at the link listed below.
It ohm tests at 570k. Now changing the KS on the Maxima can be done in minutes -- so I am more likely to take a chance on an ebay part for an item that is easily changed. So I try to gauge the part replacement purchase on ease to replace. Standard Motor Products makes the BWD brand knock sensors that I've used on the Maxima and I30 without a problem. I've paid about $70 for BWD brand a couple of times through local parts stores.

I didn't take any chances on anything under the Q's plenum. I did find a new KS wiring harness that I wrapped with heat/fire resistant tape then covered with flexible heat resistant conduit and wrapped again with XT-10R Silicone Tape.

Silicone X-Treme Tape™ fuses only to itself and creates a permanent air and liquid tight seal. ape is excellent for wrapping cables and wire, will insulate to 8000 Volts, will not melt up to 500F (260C), and withstands UV and weathering like no other tape.


http://www.ebay.com/itm/271054838609?ss ... 1439.l2649

It looks like a varmint chewed on the old knock sensor harness in the picture below. There was only two strands of wire left to make a connection on the old harness.



Old to new harness comparison after the heat retardant insulation layer enhancement.



Installed with new knock sensors.



The vacuum tube to nowhere was vatted and powder coated ready for the Y hose. A new water pipe to feed the heater hose was also installed. The heater hose pipes actually come nickel plated from Nissan. This pipe's nickel finish was polished and coated with a clear high temp engine enamel through a multi-round baking and cooling process. The steel radiator hose connection was nickel plated and coated with a baked on high temp clear engine enamel.

[Eskimo91q45]

whoa thats awesome ill give those ks a try im getting ssad its apart for this long