Throttle position sensor question

[Q45tech]

"catalyst substrate with ultra-low heat mass for quicker catalyst light-off In addition to improving the washcoat (precious metals and other elements) of the catalyst positioned directly downstream of the exhaust manifold, the thickness of the substrate walls has been reduced to an unprecedented dimension of 2 mils (approximately 50ìm). The ultra-thin walls reduce the substrate heat mass, making it possible to shorten catalyst light-off time to around 10 s, compared with 20-30 s previously."

http://www.itepsa.com/samples/SIET19990 ... s/...N.PDF

[Q45tech]

Thus the errors and fallacies in over the INET diagnosis.We probably missed something simple: a hose, a wire

But when things are out of the ordinary even T3 resorts to parts substitution.

By the way the 94 with similar symptoms seems to have been solved with the MAF replacement...........we always wait a week before declaring success.

[texasoil]

One thing overlooked is badly clogged up intake valves. It is amazing just how much crud can quickly accumulate from a few tanks of bad gas. It will cause low power, sticking valves (rough running) and be confused with lots of other causes. Check the intake manifold vacuum at idle (17-18" min) and mid RPM (18")to ensure the engine is really sucking in the air. Plugged exhaust will show normal vacuum at first, falling as back pressure builds. Dirty intake valves will show low vacuum (12-15"), getting worse with speed, but not decaying at a speed like exhaust plugging.

[elwesso]

Ill pick up some seafoam and when he comes to my house we'll run some of it through there.....

[VA99Q45]

I had a similiar idle problem a while back. If I run hard and stop at the stop light, the idle was eratic. I started to have the idle problem righ after I pumped gas from a brand new exon gas station. Using BG44k and texaco gas fixed the problem. You may want to use 2 can of BG44k on 2 consecutive gas tanks.

[texasoil]

dirty/bad gasoline causes more driveability problems than anything else. It fouls injectors and engines like sh@#.

[areznik]

Ordered MAF yesterday. When it arrives in a few days, I will meet with Wes to swap the MAFs. If its the problem I will put mine at his place. Meanwhile there is a weird thing going on. When I connect voltemeter to tps the eratic throttle reponse dissappears. The car just doesn't have enough power but at least it is driveable. Checked tps voltage again - it gave me only 2.95v in WOT this time. Then I drove it for 15-20 mins. After this it showed 3.05v in WOT. I will buy two cans of BG44K and use it in two consequtive gas refills. I pump at philips 66, does anyone know anything about their gas? Which are the "well tested" pumps?

The mileage is up to specs. On highway about 22-23 mpg, and in the city 13-14 mpg. Replaced air hose (the one that sits on the L-shape metal outlet), seemed like it was leaking air. The idle became smoother, but still no power.

[texasoil]

have you checked the battery voltage under load? You MAY be running very marginal voltage due to poor connections, bad battery, failing/slipping alternator. Low voltage cuts havoc with these electronics.

[elwesso]

I met up with andre today and drove his car. First off his car is in really nice shape (ohh to see Q leather not ripped is wonderful), hes a great guy and doing all the right things but this Q is really demon possessed... hey Im catholic maybe we could do an excorcism!

Symptoms: Car idles good, but is really struggling to run... Idle smooth, runs quiet, everything is normal... the car revvs very slow... Doesnt really shake, but it really is struggling to go... The car responds to shifts fine, kicks down normally.....

First thing we did was swap the MAF. No good.. My maf is good, and we put his maf on my car... Same thing, still very slow.....

Then we swapped the ECUs. Mine is a cal, his was a federal.. No difference in running..... He has a knock sensor code though.....

Then we checked fuel pressure. Just fine, around 34 at idle and 44 at WOT, fuel pump is nearly silent.....

Then we checked the TPS. we checked the resistance and votage and its about the same either way.. I cant remember the numbers (it was like 10 mins ago) but his was running just a little less than mine.. SOmething like 2.4 volts his was running and mine was like 3.4 or something along those lines.....

We then sat down to nice BLT lunch that my mom prepared for us!

Before hand I did an AT CHECK just for kicks and giggles, and I got a CODE D which means low battery voltage, or the battery has been unplugged for a while. This told us that the battery could be bad (even though its newish), so we checked the voltage, and it was like 12.5 just sitting there... We turned it on and it was like 13ish....

Then we swapped in my battery, and no difference there either......

So in summary we can conclude its NOT:

The ECUThe MAFprobably not the TPSbatteryfuel pumpinjectors

I am completely stumped and have no idea what to do...... Masters lets see what you got!

[areznik]

Met with Wes today. He is a great guy and I truly appreciate his help. I spent about four hours at his place and did all the things that Wes described in the previous reply. When I came home, I did the AT diagnostic again, and it didn't show any error codes this time.

I just have no idea what to do ... .

[elwesso]

If we dont get many leads we can start a new thread......

[texasoil]

check the manifold vacuum at idle and 2500 rpm to see if the sucker is breathing. Could be really clogged up intake valves.

[areznik]

Something I noticed today. When I start the engine, the fuel pump gets REALLY laud to pressurize the fuel lines. It sounds like somebody is drilling into the metal. This lasts for about 5-10 secs. I don't know if this affects anything but it definitely sounds abnormal. Wes, we didn't hear this sound when I was at your place. But again, the fuel pressure was normal. This is a new present that my Q threw me today. Maybe it points to somethings ... . Any ideas???

[squeefoo]

Check the vacuum, try a fuel filter. Has it been changed?Bad Knock sensors will make it slow, so will clogged EGR and dirty TB.

[texasoil]

Did you check the TPS at differnet throttle positions? A faulty one will normally throw a check engine light, but? Clogged fuel injectors and cruddy intake valves will choke it down. What does the O2 sensor outputs look like--it is controlling or not.

Check the intake manifold vacuum--if the timing chain is a tooth off, the vacuum will be way low. If valves are clogged, vacuum may be OK at idle, way low at higher RPM's.

Ignition timing late will also drastically reduce power. I presume you have checked things like dragging brakes to rule them out. If engine is 'normal' in neutral, but sluggish in gear--look to brakes or transmission. Dragging lock up clutch in torque convertor chews up lots of power till it cooks.

[areznik]

TPS gives the correct voltages, the same as on Wes' car. So, I rule this one out. Both O2 sensors are new. I rule these out. On March I did air and fuel BG clean up service. Just five minutes ago, I disconnected the air hose from PCV and check with finger if its taking any air. I didn't feel anything at all. The rpms drop a bit and I block the pcv. It seems that its just not sucking the air?? Could it be bad timing - because after the dealership "adjusted" my timing this problem appeared. Also, the air hose before the PCV and the inlet where the PCV sits are wet in oil. It is normal??

Today I bought BG44K and poured it into the tank. However, now it seems that air is the problem. Any suggestions how to proceed?

[texasoil]

ah ha! now we are getting to the bottom--the problem showed up only AFTER the timing was adjusted? well, that's the first thing to have checked.

Rule 1 if things get worse when something is 'adjusted' or 'fixed', it wasn't done properly.

Rule 2--See Rule 1

Put a vacuum gauge on it and check the vacuum (between the throttle plate and the intake valves. )

[elwesso]

Andre.. Go to walmart, or the closest place around here that has auto stuff, and get some SEAFOAM in the can OR marvel mystery oil (its the same stuff) and do the procedure just like I told you.....

[squeefoo]

Is it a new fuel filter or not?

[squeefoo]

Is it a new fuel filter or not? BG 44k won't clean out the fuel filter if it's clogged.

[elwesso]

His fuel filter is just a few months old, and not many miles.....

[squeefoo]

It was never mentioned. Clogged converter ? How the H*** did I double post !!!???

[Aus94Q45]

The PCV valve may have some oil and deposits. Overall this sounds like a timing problem to me. Engines will run flat or lose acceleration and top end with improper timing. Couple of thoughts -- the knock sensor codes jump out at me here. That has to be taken care of for the integrety of the other diagnostics. THey adjust the detonation. Further Dennis has stated that Q's go flat with bad knock sensors. Also, have the under plenum hoses been replaced? Lots of vacuum leaks to be had. Also, even though the fuel filter has been replaced recently, it can clog quickly. ALWAYS start with the easy stuff. Also, "after the dealership "adjusted" my timing this problem appeared" says to me (a) bad timing adjustment; (b) they left off a hose or some other connector. Have the timing adjusted again.

[elwesso]

I think aus is on to something

His plenum has been removed about 3-4 times in the last 2 years..... Thats puts a lot of wear on the hoses...

When the KS go bad it doesnt make it run this bad...

I think maybe a KS inspection and maybe a really good plenum clean are in order...

[Q45tech]

Look at the CAS top front: the position adjustment slot is roughly 3/4" long that's 45 degrees of adjustment range.

15 degrees BTDC is roughly when the left of the screw shows 2/3 and the right space is 1/3 exposed.

I can imagine a tech might get the timing wrong by 1,2,3 degrees but not enough to show your symptoms. They see the CAS all the time [when checking for corroded connectors] and they know what looks about right.

Because it is difficult to loosen the 3 screw bolts without double swivels it doesn't just get randomly adjusted because of the special ingition transformer necessary to couple a timing light to the system.

[areznik]

Just took it to local Nissan dealership. Tech adjusted timing, he said it was a fraction off but nothing serious. We drove the car, and he connected consult tool to it. He said that everything is nearly perfect. Tps is working properly, air fuel mixture is excellent, and no error codes. He told me, that to him it seems that my Q is just fine - yeah right, you can tell he never drove Q before.

I replaced PCV - no change. I was wondering, I have bosch platinum 4 plugs. Should I switch to NGK, I mean can it make the difference?

[squeefoo]

Huge difference, I didn't think so until I did it. It had Autolite Coppers in it, when I got the car, it seemed okay, but the difference for me was huge. For the right plugs at the right price: Wes. To check for vac. leaks squeeze the hose like the FSM says, that worked for me too.

[squeefoo]

PS ! Bosch +4 plugs are very bad for this motor, do a search.

[Q45tech]

Bosch +4 the destroyer of Q.......let us know how many electrodes were burned off [4x 8=32 chances]. Not every time but often enough to be scarey.

[texasoil]

until you check the intake manifold vacuum at idle and steady 2500 rpm you will not be able to determine if valves are crudded up or cats plugged.

Fuel air mix at idle being OK does not mean its OK at other conditions. Plugged fuel filter will pass enough for idle, not enough for any power.

It always pays to check basics first--filters,hoses, timing, intake vacuum--then hunt for other subtle failures like plugged cats and electronic stuff based on the fundamental test results. Phsyics of engine performance have not changed in 100 years, only the precision of adjustment of parameters to optimize combustion.