92 Q45 loses power after short drive

[werepe]

Hello to everyone! My Q is at it again. It loses power drastically after 15-20 minutes of drive. It starts right up, runs smoothly...then out of no where, a drop in power. It starts to hesitate from thereafter. I'd turn it off and then on again with no changes. It only runs smoothly from cold starts up until it loses the power and that's all she wrote from there. It doesn't cut off while it's on but the lack of power feels like it wants to. Qs are not fun to drive when the power is compromised. I've changed the injectors, the spark plugs were changed a year ago.What could be causing this? PLEASE HELP!

[goody90q45]

Is the CEL coming on at about the same time? If you haven't pulled ECU codes yet that's probably a good first step. I'm going to take a wild guess and say you'll find an EGR code.

Your drop in power coincides with the 15 to 20 minutes of driving/engine warmup it takes before the ECU tells the EGR valve to open, the timing to be retarded (or is it advanced?) and let emission gases back through the intake. Make sure the intake path is clear of carbon depisits from the exhaust manifold, through the EGR valve and into the plenum.

I had a similar problem when I first bought my 94Q. One of the vacuum hoses from the small rectangular solenoid was disconnected, plugged with a screw, and shoved under the plenum making the EGR valve inoperable. If your EGR path is clear your next step is to troubleshoot the solenoids and vacuum hoses feeding the EGR system.

[alexander]

Check the Knock sensors too.That's the problem with my 96 Q.It has been to many Infiniti service techs over two yearts, only last week did they discover a code for the KS, while on a test drive. Same systoms as yours.

I thought the computer stored these codes for future diagnosis.Guess service only checks when I tell them exactly whayt to do.Or, are the codes not stored?

[qship96]

Knock sensor codes are stored- even a cheap $40 generic OBD2 code reader purchased from any auto parts store can read them=== every 96 and newer owner should purchase one as it works on every brand/model of car built since 1996 and can save you much time and expense.

[Infinitiguy19]

Or even bring the car to autozone and let those idiots check them while YOU WATCH THEM do it so they some how don't screw it up.

Thats for the poor Q45 owners, Wow an oxymoron.

[alexander]

Well after giving the advice I got about the Knock Sensors, and the possible $1880.00 service fee, I just took the Q to the Infiniti in San Jose.Service manager said my interminent performance problem would NOT be caused by the KS. And a code could come up and be the wrong code. He said if it was the KS', you could barely drive the car.Since I can drive it and only have the lack of power only half the time I drive the car, 'it could be a list of things.' And since he saw on record all the stuff I have had paid for already, he suggested not to put another dime in the car, except maybe oil.He asked about the last service at a different Infiniti who diagnosed the KS fault code.(Niello) He commented that they didn't even record the service on Infiniti's computer.He also stated NOT to use that BG44 cleaner, which I have, as they have had to replace seals long ago on these old Q's that Infiniti attributed to the cleaner and even had a recall on the injector seals. (Don't recall that one).Hard to believe anyone now, and this guy was not trying to take my money, nopr sell a car to me.At least he didn't charge for this inspection.So back to square one.

[werepe]

thanks everyone for your input thus far. I replaced the EGR valve and still got the same issue. The car is still having the same symptom. I checked all the vacuum lines leading to the valve. The EGR valve path was clean and also the pipe coming from the manifold had a clear path. Nothing was blocking anything. I went ahead and olm tested my knock sensors. Result: 1 read 533K and the other was 538K. Are these knock sensors bad or the readings are within the norm? Please advice.Thank you!

[qship96]

your knock sensors are working correctly based on your reported figures

[maxnix]

I checked all the vacuum lines leading to the valve. The EGR valve path was clean and also the pipe coming from the manifold had a clear path. Nothing was blocking anything.

I (ohm) tested my knock sensors. Result: 1 read 533K and the other was 538K. Are these knock sensors bad or the readings are within the norm?

But you don't know if the opening into the manifold is clear unless you pressure tested it.

KS are OK on the ohm test.

[Q45tech]

When you say loses power, do you mean partial throttle or wide open throttle. How much does a stop to 80 mph change in seconds [stock around 11 seconds] after hot..............................each 0.1 would be around 10 HP.

[jackk32]

Just curious if you found the problem my 91 q doing the same thing

[Q451990]

If I had to make a guess, I would say it's somehow fuel related... maybe a bad FPCU that only acts up as it gets warmed up?

Heath

[Q45tech]

We routinely attach a fuel pressure gauge to windshield and monitor for a 15 minute drive when we duplicate conditions.

Since WOT has an A/F of ~~ 10 to reach 14 requires a PSI drop from normal ~~44 psi to about ~~ 20 psi..................this won't show up at idle or cruise since the flow is so miniscule under these conditions.

[silkysmoothyjud]

I have a 94 in which I had to replace 4 injectors, heat changes injector performance considerably in my experience. Could cause rough idle after warm, low throttle response. 93 Q, if not MAF (stall) it's the injectors...probably whole rail. Common prob with 93 or younger. DONT BUY USED ONES!! DONT BE TEMPTED. Unless you like to do things 4 times....Like I had to do..

[maxnix]

hey, my 1993 nissan altima gives a code 34 even after i replaced the knock sensor and runs fine for about 20 min. then dies a slight acceleration under load

I guess the point is, besides you are lost, did you check your fuel pressure?

[silkysmoothyjud]

I noticed you said you changed your injector rail; PLEASE tell me you bought new ones

[silkysmoothyjud]

and to the guy who changed his KS; did you change the harness as well? If not, DO IT!! Its part of changing the KS. I did that one right the first time...thanx nico.