Q45 (1994) - Knock Sensor Replacement: ECU Reset?

[Mint Q45A]

Basic question: After replacing the KS do you need to manually reset the ECU to clear the code? Or does the ECU "hear" the KS and clears the code automatically?

[Q45tech]

The KS is constantly checked and the ecu is reset at each crank cycle........the stored code will erase when 20 cycles without a new failure have passed..............the ecu will resume normality when it hears and sees the KS [both] working.

[Mint Q45A]

Q45 Tech, Thanks a lot for your quick response!

[1990Q45'r]

On my 90 Q45 California model I was getting "34" Knock sensor but, also had "45" injector circuit at the same time.Is it due to the "leaning" by computer?

[Q45tech]

The only way early CA ecu had to GUESS at an injector leak was if the adaptive learn went lean to try to compensate for one banks excessive richness.

When you have the rail off to replace both KS and their harness you use the fuel pump to pressurize the rails with connectors disconnected and look for leaks.

Probably just old slow switching O2 sensors but in CA you never know concerning fuel.

[1990Q45'r]

I will check the injectors off. There is another code, "51" code, injector leak. Wonder how it differentiates? The old sensors read 6 meg and 1/2 meg. Spec. is +10 megs?Bought replacement sensors on ePay. The new knock senors only read 1/2 meg. I didn't see any complainers.

[qship96]

Are you talking about knock sensor resistance values? I think proper functioning ones should read about 550k ohms

[1990Q45'r]

qship96,Yes, mine read 500k . Now I see the manual states an ohmmeter that can read +10Meg. Doesn't really give actual ohmage of knock sensor in manual. Sounds good.

[Mint Q45A]

What would a higher resistance mean? How would it affect the performance of the car?

[goody90q45]

What would a higher resistance mean? How would it affect the performance of the car?

KS are going to read in the 500k-550k Ohms resistance range or they're going to read zero. There will be no in between.

I have no experience replacing them other than what I've read but having two good KS will greatly improve acceleration. I've had one dead KS since I bought my Q but haven't gone deep enough under the plenum to replace it yet. I have great acceleration now and am looking forward to an improvement when I get them both replaced. KS are also insurance against an errant tankful of 87 octane gas and will advance (retard?) the timing to eliminate knock from using low octane fuel.

[3Q Jay]

retard.no, not YOU!

[artandscience]

Ok, so color me ignorant.

If I get a code 34 (knock sensor) and it remains after 20 restarts, then it is likely that my knock sensors (and harness) need to be replaced?

Thanks, Stefan

[silkysmoothyjud]

take the "If" out and your a freakin guru!!!

[Q45tech]

"is likely that my knock sensors (and harness) need to be replaced?"

Every 90-96 Q45 will need new KS and harness eventually..........whether at 80k or 180k or in between is a function of ambient temperatures and number of overheats.

Almost as common as the need for new plenum and fuel hoses.

[silkysmoothyjud]

I got a KS and a leaky injector code. I got my KS installed (with the harness) and I pulled my rail to check for the "leaky injector" and nothing. No leak or nothing at all. With the plenum off, I saw several small hoses disconnected and several large hoses split. Would broken hoses and/or air leaks cause the "leaky injector" code?

[Mint Q45A]

Out of curiosity - once you pulled the fuel rails, how did you check/test for any "leaky injectors"?

[Q45tech]

Leaky injector code usually means an old sluggish worn out owner abused O2 sensor. One checks the adaptive learn %..... the deviation from 100%...........which is the amount ecu is adjusting the mixture from brand new preprogrammed values..........too much fuel can mean a sluggish O2.

One then examines the O2 waveform switching back and forth ^v^v^v where you can observe only the 4 cylinders per bank.

Injectors don't leak but their O rings do, but this usually means the cylinder gets hydrolocked.

REMEMBER oem codes were designed for NEW CARS to trouble shoot not obsolete out of warranty cars worn out with more than 70k!

[silkysmoothyjud]

Thanks for the input Q45 tech! I was feeling a vibration that came and went, it was kinda revolving. I pulled my KS and they had several hair line cracks in them. My idle was smooth. I was only getting about 11 mpg (average) with a cel that only came on when I took my Q a distance longer than 5 miles. Sometimes, if I gave it gas when doing over 55 mph, my Q would fall flat on its face with no acceleration. I stopped and finally pulled the plenum. Q45 Tech explains how to check for leaks earlier in this post, but he is right, if the injectors were leaking you would freaking destroy your Q, blue smoke would be pouring out the tailpipe if gas were leaking past the lower o-rings, and one would visually see the gas leaking through the upper o-rings. I ordered my hoses from Joe. I will report when finished, and I will go to Q45.org to prepare for o2 sensor replacement....

[Mint Q45A]

Dennis' approach to test for leaky injectors using the fuel pump to pressurize the rails once you have them off the plenum makes a lot of sense. You just need to use some fuel hose to rig each rail. I was just curious on how to deal with the pressurized fuel once yo are done with the test - basically how to release the pressure from the rail without making too much of a mess or a hazard...

Note: I found out that if you have a leaky lower O-ring there's some minor carbon deposit around the outside of the opening, on the fuel rail itself (looking at it from the tip of the injector). When you have good Injector/O-rings, this part is usually very clean... at least that was my experience....

[silkysmoothyjud]

You need not disconnect the rail in order to test it, just turn the ignition key (do not turn it over), light up your dash and prime your FP, and with some safety glasses on and your fire extinguisher handy,visually check for leaks.

[silkysmoothyjud]

The job is finally done!! Three weekends and totally freakin worth it!!! The car makes more use of its power with new ks. No cel (yet) and another thing, no strange smells in wot. That under plenum hose and gasket work has totally paid off. Also, the egr valve, one should check the connection on the exhaust mani to make sure its secure. Mine was about to fall off from just moving it back and forth. A big thank you to Wes for his unwavering support, and to q45 tech for his advice....75 mph no problem in second gear and very loose in all gears again, it wont hesitate to red line!!

[Q451990]

A properly running Q is a thing of joy! I'm glad to see you got everything fixed!

Heath

[silkysmoothyjud]

Could a loose EGR tube on the manifold cause the "leaky injector" (o2 sensor) code? Mine was looser than a three dollar whore on Friday night. If so, could said issue cause permanent damage to the drivers side o2 sensor? This is total, freakin total post mortem.....

Revolving vibration still comes and goes, sometimes harder than others, sign of o2 sensor problems, cel blinked for a second and then went out, I do not think I will even need to pull the code. And Dennis shall have the last word......
Modified by silkysmoothyjud at 8:54 PM 1/31/2008

[Q45tech]

O2 fail and get sluggish much more frequently than KS get replaced because it is easier and less expensive.

The more expensive things are the less like they are to get replaced, as long as they don't stop from cranking.running......even badly.

[IRVING GRANADOS]

The job is finally done!! Three weekends and totally freakin worth it!!! The car makes more use of its power with new ks. No cel (yet) and another thing, no strange smells in wot. That under plenum hose and gasket work has totally paid off. Also, the egr valve, one should check the connection on the exhaust mani to make sure its secure. Mine was about to fall off from just moving it back and forth. A big thank you to Wes for his unwavering support, and to q45 tech for his advice....75 mph no problem in second gear and very loose in all gears again, it wont hesitate to red line!!

hi i hope you still , reading this forum i have the same problem with my 1990q45 and my question is are they 2 or 1 sensors? i mean ks
both are the same ???

[please help . anybody knows>? what else i have to replace when i start working on it?
irving thanks

[Q451990]

Both sensors are the same. I would replace the knock sensor sub-harness, as well as any deteriorated rubber hoses under there - probably all of them if the plenum hasn't been off in a while.

Heath

[IRVING GRANADOS]

Both sensors are the same. I would replace the knock sensor sub-harness, as well as any deteriorated rubber hoses under there - probably all of them if the plenum hasn't been off in a while.

Heath

thanks for the info . I been fixing my car with my friend , and every time we find something wrong wit the car, we have this codes 14 & 34 and i replace 2 times the speed odometer sensor (use ones ) and still is not good , i have speed odometer problems, but i hope the KS helps + a new speed odometer sensor,

thanks for you Reply Sir . BTW I HAVE 1990 Q45 WITH 154897 MILES AND I LOVE MY CAR ;-)

[Q451990]

It might be worth swapping in a different instrument cluster to see if that clears up the problem...

Heath

[IRVING GRANADOS]

yes i did replace the cluster too. the screen in my car says transmission malfunction, and the code 14 is the vehicle speed sensor , course i have shift problem , i have to go step by step . do I have to change any other gasket when we replace the KS ?

[Q451990]

Not for the knock sensors themselves, but there are plenty of things that will need replacing. Check out some of the "plenum" threads, or just order what you need after you pull it apart...

At a very minimum, I would replace the throttle body gasket, and the plenum to runner o-rings if they're brittle. You will also want to replace the cooling hoses that cross between the heads, since you'll have to remove them to get to the sensors.

Heath