Throttle position sensor question

[areznik]

Hey guys,I have something weird with my Q '94 (109K). If I push it a little bit more than usual to 85-90mph and then stop at the stop light, the idle drops so low that the whole car vibrates (not every time but one out of five times). Unrelated to idle drop, sometimes it smells like a sulfur (all injectors are 1 year old, fuel pump 1.5 years old, and egr valve one year old). If I restart it, everything is normal. I have new O2 sensors, just cleaned IAC valve and the throttle body with BG product. Also, air hoses seem to be clean and pcv vavle looks good (not sticking and clean). After reading numerous posts, it seems that some people resolved similar problem by replacing TPS. I also know that there are two screws that I must not touch, are these that hold the TPS? Also, there are two TPS switches, one primary (for engine control) and another one secondary (for TCS). Which one may be faulting and what is the procedure to install the new one (i.e. how do I make sure that I tight it in the right angle)?

Also, is there anything else that I should check before going with the TPS replacement?

Any reply will be greatly appreciated,Andre.

[Q45tech]

Sure the Consult has a TPS test proceedure: measures closed and WOT voltage then you data monitor to set precise voltage at hot idle correct rpm.

You have A throttle blade TPS and AN auxillary TCS throttle blade TPS ---- checks sets TCS motor position.

[areznik]

Today, when I hit full throttle and drove 90-100mph for 10-20secs the car started shaking when I stopped, and then the vibration slowly dissappeared by itself while I was standing (it took it 10-15 secs until the car was calm again). Does it sound to you like a TPS problem or maybe a weak fuel modulator?

P.S. It there is a strong smell of sulfur like odor when it happens. At times I can accelerate fast but not keep the high speed for more than 5 secs and everything is fine. I noticed that the problem occurs when I keep high speed for 10 secs and longer.

[Q45tech]

What is your fuel pressure under these driving conditions? Tee into the line after the filter and tape the gauge to windshield!

Never seen a weak fuel regulator or fuel pressure dampener.......seen lots of worn out bad fuel pumps and clogged up fuel filters.

Lean running can destroy cats fast [Sulfur smell].

[areznik]

If I check the amps between the terminals of the fuel pump fuse, will it be good enough to tell if the fuel pump or the fpcu are bad.In another thread you said that a good fpcu should provide 2.1-2.6 amps between the terminals of the fuse while driving. Do you think it will be a good test?

[Q45tech]

The best test is to look at the current waveform and pump rpm under load and cruise.Pressure is the easiest test to do and tells you if there is a pressure drop as the rpms climb...........all that really counts is that it maintains the correct 44 psi at highest demand 6900 rpm!

Cruise is not demanding on the pump.

The pump has [should have] a 14 times difference in volume flow from idle to cruise to WOT .

[areznik]

Here is what I did today:Connected voltmeter to measure amps between fuel pump fuse terminals and these are the results (engine warmed up):1. Switch on (before cranking) - 2.8 amps for ten seconds, then drop to zero.2. When cranking - 4.5 to 4.8 amps.3. On idle (in park or neutral) - 1.96 /+- 0.01 amps (feel minor vibration but not too bad).4. When standing still (in drive) - 2.05 /+- 0.01 amps (feels very smooth).5. Cruise without load - 2.3 /+- 0.01 amps.6. Full throttle - 3.5 /+- 0.01 amps.

The interesting thing is that after accelerating whenever I leave the pedal the amps drop to 1.92 and one time it even dropped to 1.89 amps (noticable vibration)! When I completely stop the amps raise to 2.05 and everything feels normal. When driving, if I don't touch the pedal the amps drop to 1.92 and feel a minor vibration. From other posts it seems that 1.92 amps is too low and you said that it should not drop below 2.3.

My question - is this the fpcu?? I replaced the fuel pump about a year and a half ago (it was humming like a cow) but didn't touch the fpcu.

[Q45tech]

The FPCU seems to be working fine [from the amperes you provided] still doesn't mean the pump is providing the correct pressure/volume.

Full throttle at what rpm [3.5 amps] all the way to redline?

What is accurate hot idle rpm in park and in drive rpm........inside tach not accurate enough to answer this question!What is IAC percentage at idle in park, % with AC turned on?

Again what is fuel pressure? One you measure the WOT pressure we can affirm the pump is ok.........not till then!

[areznik]

Just finished with the fuel pressure test procedure. Teed after the fuel filter and took the gauge inside (the hose was long enough maybe 3ft). Here are the results:1. Key on, before cranking - 34 (35) psi.2. When cranking - about 42 psi.3. When idling in park or neutral - 34 psi.4. When standing still in drive - about 35 (maybe 36) psi.5. When accelerating about half throttle, goes up to 40-42 psi.6. Full throttle to the red line - about 45 psi.

When release the gas pedal and cruise, the pressure drops back to 34 psi. It never dropped below 34, and never suddenly dropped when accelerating. Drove it for about 15 mins, and it started vibrate somewhat less than before but still noticeable after getting to 100mph and cruising on that speed for about 7secs. When slowing down, and reacing maybe 30mph the vibration is noticable and dissapears in 10-15 secs. The vibration is tolerable, meaning that I can drive the vehicle without problems but it just seems that something is wrong. Lately, I noticed that the cars shifts from third to fourth it does in a few steps. First, I can feel gentle shift and the rpms drop from 2500 to about 1500 (under very calm cruise) and then when rpms raise to about 1900 (maybe 15 secs after the shift) there I feel another bump like its gonna make the shift again, but the rpms remain the same.

What should I do next?? (You talked about IAC percentage of air, how can I measure it without consult tool?).

P.S. (Fuel pump is quiet, temprature outside about 80F).

[Q45tech]

Screw the IAC bypass totally in then back out 3 turns, if the idle rpm is 700 hot in park no ac the IAC and throttle are pretty close to correct and clean.

After that you need the Consult to proceed because even though you can read some of the sensor voltages with a VOM........you really must see how the ecu interpretes the voltages.

Impossible to set TPS accurately or evaluate temperature or MAF, exact rpm, etc without the Consult.

[areznik]

When IAC bypass 3 turns out, the rpms are about 1050 hot in park without ac. What happened is that about three months ago the rpms were very low and the dealer raised them to about 750-800 in park. Then, I cleaned the IAC and the rpms went up. Also, I played with CAS sensor, rotated it clockwise and counter clock wise and found the position with the highest rpms. I thought that this is the best timing for the iginition.

You said that I need consult to proceed. I have two questions, can I buy it somewhere? If not, please tell me exactly what to do and I will ask the dealer to make these tests and tell me the results.

Andre.

[Q45tech]

Have the dealer reset your [self induced] screwed up timing with a timing light and the special Q45 timing light adapter.

"played with CAS sensor, rotated it clockwise and counter clock wise and found the position with the highest rpms. I thought that this is the best timing for the iginition"

The worst scientific proceedure I've ever heard of........you probably will get the NATIONAL NICO annual award for worst performance by an owner contributing to engine misbehavior!!!!!!!!!!!!!!!!!!!!!

Just like the IAC precise required setting the ecu varies the base ignition advance [after you set it at 15 manually] to make fine adjustments in idle.

Like pulling teeth to get owners to admit that they turned this and that to see what would happen. After hours of diagnosis sometimes days the tech finally find it and the customer says oh yeah I tried to fix it with a screw driver.

Please God tell me you didn't fiddle with the screws on the Throttle Body?

[areznik]

No. The screws on the TB are untouched. Do you think that reseting the timing by the dealer may solve the problem?

[Q45tech]

The ecu expects the timing to be between 13-17 degrees BTDC MAX MAX MAX. If you moved it even a fraction as the 3/4" slot allows an up to 45 crank degree adjustment. So 4 degrees is +- 0.03"----0.033" total range of movement out of 0.75".

Setting it accurately to 15 degrees +- 0.5 is a real challenge as it moves when you tighten down the 3 screws.

Peaking the idle rpm with timing probably means you are over advanced by 10 degrees or so. No wonder ecu is pukeing.

[areznik]

I set an appointment for tomorrow (5/25) afternoon with the dealership in Indianpolis. Is there anything else that I should ask them to check while I am there?

[Q45tech]

My 3 turns out on the IAC bypass screw is a rough and dirty way to set it........remind the tech that you would like to see 10-15% IAC duty cycle [AC off].

Print out the whole thread from NICO and have him read it.

The History will help him!

[areznik]

Today it was a very long day with my Q, but nothing came out of it. Took it to the dealership and the tech reset the timing and the idle. Then I drove with him and the vibration problem appeared right when he was driving!! He kicked down and pushed it to 60mph and thats where it was. He said that the car has very low power and even measured the acceleration. It took it 11 secs to get to 60 from complete stop!!! He connected consult and repeated the acceleration where the car shaked again. Unfortunately, he could not find anything unusual even with consult connected during the vibration. He checked fuel air mixture during the vibration and it was normal, he said. Checked resistance on injectors and these were fine. The weird thing that he said is that the lifters which are under the valve covers might be bad?! He said that on one of his Q he had similar problem and replacing all the lifters solved it. I got a feeling that he was trying to lure me to get $2500, because I never read anything about it here at NICO. Eventually, he said that he didn't know what is wrong with it?!? When I took it home I felt that the throttle is not responsive at all, meaning that I can press the pedal about third way in and there would be almost no reaction from the engine. Also, I noticed that it likes to shift to higher gear when I press gas. Say I am driving on third at 2000 rpm, and then when I significantly press the pedal it shifts the gear to fourth and the rpms drop to 1500 which makes it much harder to accelerate!! Weird, it seems that instead of downshift it upshifts!

Now I am really confused because I didn't get any answer from the tech and the car drives much worse than yesterday. I read other posts and it seems that the tps is not responding correctly.

What should I do? I am lost.

[Q45tech]

Even if it was running on 7 cylinders it wouldn't take 11 seconds to 60 mph. Each cylinder puts out about 40 lb/ft maybe running on 4 cylinders

Did he do a Consult power balance?Now you get to check compression and leak down and back pressure prior to precats via a gauge with hose screwed into oxygen sensor port.

Did he do transmission diagnosis with Consult?

Might take 8 hours to find the problem........lots of test to do.

TPS test on Consult only looks at closed and open, but with Consult on data monitor you can see the actual voltage change in 0.00 volt increments as you press the accelerator same loking at transmission analysis except you see 1/8, 2/8, 3/8 etc all the way to 8/8.

Think this tech lacked the expertise to deal with the Q. Find another dealer or ask to deal with their most senior , if this guy was it run away fast.

You could rig a wire on TPS variable terminal route into cabin and with a voltmeter measure the 0.4> 1.2>4.0 VDC as you vary the throttle position.............with the relatively low cost of TPS I would just swap and recalibrate............in case it has some worn spots where voltage drops out or is erratic.........

The TPS is the only variable to acceleration you mat have hit it on the head..........of course the TPS could be good but the ecu bad swap tps first. Then a spare ecu.

Nice to have another WORKING Q to compare voltage and Consult readings.

[areznik]

Today I checked the tps (for engine control). I disconnected the grey connector as shown on the picture and checked for resistance and voltage between terminals b and c. The resistance followed the normal pattern from 0.7K ohm on closed to 5 k ohm with WOT. However, I could not find ANY voltage (zero all the time). Battery voltage is 12.7v. From voltage perspective the tps didn't respond at all. I have two questions. Fist, did I checked the voltage between the correct terminals (if not, between which two should I check)? Second, is the resistance check good enough to tell that the tps is good??After the check I drove the car for five minutes. When I drive at 15mph and hold the gas pedal steady the car seems to accelerate and slow down on its own?? Feels like I am playing with pedal. Also, at times when I press the pedal - there is no response. At all times - the car drives smoothly, means no vibration at these lower speeds.

[Q45tech]

Finish the diagnostic proceedure from FSM, the 5 volts [reference for all sensors] from ecu to to terminal.

Back probe the plugged in connectors to make sure you have 0.4-0.5 volts at idle feeding ecu

5 volts from ecu feed one side, the other side is ground and the movable wiper on potentiometer returns the position [voltage to ecu].

The resistance test is good but due to resolution you might miss a worn bad spot where the change is not linear.

Why I use the consult [vom] to read a steady progressing voltage with fine movements of accelerator.........if it wears anywhere it will be in the 0.4-<2.0 volt range because that is where frequent foot action is.

[areznik]

Checked the tps voltage today. When I was pressing on the idle roller just slightely and raising it maybe to 1500 - 2000 rpms, at some point it started surging (like droping and then trying to get back). The voltemeter showed inconsistency in voltage - it was droping from 0.52 to 0.48 and then going back to 0.51 .. 0.52. In general, after the timing reset the engine vibrates more and it feels like its struggling to hold the rpms constant.

I ordered the tps ($123.45) and it should arrive in a few days. Truly hope that it will end this nightmare.

Dennis, want to let you know that you are a great help and I would be stuck forever without you. I appreciate it a lot.

[Q45tech]

I don't think 0.48-0.52 is significant, essentially the throttle position might be resolved to 5% steps........20 stepsDoing the tps test with no road load is inconclusive, as the problem occurs at speed right.

0.44, ...................................................................................4.44

so 0.2 volt steps might be the 5% steps.

The A to D in ecu actually can resolve 255 steps so maybe 0.02 matters but not enough to throw a fit.Normally if a sensor reading is within 10-20% of the preprogrammed value ecu adapts and proceeds to calculate a suitable injector open time.

Today I was troubleshooting a 94 with similar problems turn out that the MAF was intermittent and read 20% too high at times.

If you can find another 94-95 MAF without buying a new one yet, a swap test might be in order.

Impossible to test without Consult as I have to look at MAF voltage, rpm, TPS, both banks of injector opening time and my notes and do some mental calculations SIMULTANEOUSLY with a driver following accelerator commands..........injector opening times above 11.3 millisecs in hot weather at 4,000 rpm are suspect, when they hit 12 millisecs alarm bells start to go off but more testing is required.

Don't think we/you are finished yet with TPS [being sole solution].

[areznik]

Unfortunately, I don't know anyone around here with a Q. I am subscribed to the all data website and here is the procedure that they suggest to test MAF:

Fold back mass air flow sensor harness connector rubber as shown in the figure if the harness connector is connected. Turn ignition switch "ON". Start engine and warm it up sufficiently. Check voltage between terminal 1 and ground.With the ignition switch "ON" (Engine stopped), there should be: Approximately 0.2 Volts DC. At Idle (Engine is warmed-up sufficiently), there should be: Approximately 1.0 - 1.4 Volts DC.

Do you think it is a good test for MAF?

[DAEDALUS]

Without digging around, that sounds a lot like the test given in the FSM. If you get bad results, MAF is probably bad. If results are good, then the MAF is good at idle.

[Q45tech]

That test is NO WHERE NEAR the accuraccy required to determine the MAF health. All that test does is tell you the MAF is producing some signal............the ecu shows a code [MIL] when no signal is present or if the numbers are so grossly out of wack that the engine may not run.

A 0.1 volt error gets compounded as the voltages rises due to the exponential equation used to trans late voltage to air flow.

The exponent is to the x**3.5 powerSo 0.1 volt at 4.0 volts is over 10% more air and 0.2 volts is like 20% more air.

http://www.se-r.net/about/sent...ly95/

http://www.allfordmustangs.com...s.xlshttp://www.superstang.com/maf.htm

Really the only way to check if its accuracy is within 3% is to reverse engineer the injector opening time to known standard values at known standard conditions.

I have hundreds of data runs on my Q which I use as comparisons.

After so many my brain knows what is about right for each condition of rpm and ambient temperature.....All data is WOT so even I have to spend 15 minutes thinking about less than WOT.

All Q being the same displacement allow x amount [+-5%] of atmospheric pressured air to flow in only limited by throttle position [tps voltage], dirt in air system/valves, and rpm. Now the air's density changes with temperature.

By knowing VE at rpm and TPS and air density you can derive a correct amount of fuel.

When I see a WRONG amount of fuel [injector opening time] assuming both banks are about equal [within 0.1-0.3 millisecs] and looking at coolant temp and ignition advance, I reverse calculate what the MAF should read. Knowing that it would change 1% [not the voltage but the exponented voltage [so I can ignore 0.01 volts] but not 0.05 volts.

Each MAF is calibrated at factory to be very very accurate from 4.0-4.5 volts.

On the above web sites don't confuse Kg/Hr with the more normally used grams per sec that is the standard for OBD2 now.

255 grams per second of air is enough air to react with 21-23 grams of fuel per second to make ~~330 HP +-15 depending on the engine efiiciency [cam timing and piston area and internal friction].

http://www.ws6.com/ramtest.htm

Read down to on the technical side of this web site:http://www.samscars.com/sam-2-5.htm

[areznik]

Today I did a basic thing, disconnected all the connectors and cleaned them. The battery was disconnected for 30 minutes. When I started the engine after it, the idle was very smooth but still no power. I can drink coffee while driving with WOT. After driving it for 5-10 minutes, the idle became somewhat shaky again.

I read in different posts that bad knock sensors can reduce power. I have 109K on mine and still original ks. Two O2 sensors are new.

Before I went to that tech in Indy I didn't notice any problems with power, just occansional vibration after harsh acceleration. When I took the car home after the service it was like black and white - there was a tremendous loss in power. Is it possible that he only made the timing worse, to make the car loose this much power? Do you recommend maybe try to reset the timing again in the local Nissan dealership?

I sent email to Wes, he lives about 60 miles from me, so maybe he will agree to try and put his MAF on my Q to see if the MAF is the problem.

[elwesso]

Hey andre......

After the phone conversation and this thread, I think we're looking at a MAF problem hopefully. Ill send you an email with meetup times tonight to decide what we're going to do..... I really hope its a MAF because thats certainly an easy, yet expensive fix!

[areznik]

Checked the tps today while driving, and here are the results. When on idle, it shows 0.45v. Suprisingly, in WOT it gives only 3.4v and no more. Drove the car for 20 mins and it constantly gave only 3.4v in WOT. It seems that the tps is not giving the 4.5v in WOT and is short in about 1v.

[Q45tech]

Might be enough [3.4 volts] although I like to see 4.0 volts at minimum...........make sure the input from regulated supply in ecu is 5.000 volts to ground.

I never measure at TPS always look at what Consult says the ecu sees.......never checked if they read the same simultaneously.

Something to always keep in mind is the possibilty of:We have had a few 94-95 melt precats from wrong plugs misfiring [they both had weird plugs].

The 90-93 have one type of catalyst coating while the 94-95 have another and the 96 yet another [ I believe]. As the emission requirements got more difficult.http://www.e2.org/ext/document.jsp?docId=5085

What happened with MAF swap test.

[elwesso]

He tried to drive to my house so we could swap the MAF but he said that the car barely ran, and didnt think he could make the 100ish mile trip.....

I figured he could buy a new MAF and if it doesnt fix it he can resell it on NICO..