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Samson

77 280z Water Temp Sensor Issue, Runs Very rough

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First thing I notice from the pictures is the throttle return spring is totally incorrect, both in its location and style.

Really? Hmm. Is this big throat throttle body's return spring mechanism same as a stock throttle body? The routing/placement, what is the proper way to fix this? I looked other pictures, and the spring I have thats hooked onto the intake manifold that loops over the throttle linkage shouldnt be there, correct?

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I have a 77 also. I am unsure what a big throat throttle body is, so I am just comparing youre picture to my car. Could you upload a whole engine bay photo?

If you remove the spring (the one in the third photo) will youre throttle return? It is starting to look like this may be one culprit.

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I have a 77 also. I am unsure what a big throat throttle body is, so I am just comparing youre picture to my car. Could you upload a whole engine bay photo?

If you remove the spring (the one in the third photo) will youre throttle return? It is starting to look like this may be one culprit.

Big throat throttle body as in the "60mm upgraded throttle body" MSA offers. Do you have a picture handy of your throttle linkage setup? I will try and remove the spring in the third photo tomorrow see how that goes. As for the whole engine bay photo this is the only engine bay photo i have when the previous owner sent to me, it's kinda blurry.. i will get updated pictures though. Just bought a valve cover gasket, feeler gauge, timing light and some sea foam. Hope to do a valve adjustment and check the timing on this car I'm new to all this ignition adjustments. Even more afraid to pull the cover off and mess with the valves. Question, when i'm adjusting the first exhaust valve (i know you're suppose to put it on TDC which allows the cam lobe to point up? Correct? So pretty much every single valve (Exhaust & Intake) i want the cam lobe pointing up to make the adjustment from #1 all the way to #6 cylinder?

post-28105-14150821569423_thumb.jpg

Edited by Samson

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After work tomorrow I will compare youre setup with mine. I am sure that spring does not belong there, at least it is not stock.

I am not an expert on valve adjustment. Check some of the other writeups. I have tried adjusting the valves hot, as it should be done but I am not fast enough so what I have done is adjust them cold then I warm the engine and check for the hot specs. Adjusting the valves is not hard, it can actually be sort of fun if you are in the mood. eachl lobe should point up when you check clearance. use a remote starter to make life easer. Also it will be a good time to visualy inspect the valve train.

Also do not be alarmed if the rockers seem to be loose when there respective lobe is up, this is normal.

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After work tomorrow I will compare youre setup with mine. I am sure that spring does not belong there, at least it is not stock.

I am not an expert on valve adjustment. Check some of the other writeups. I have tried adjusting the valves hot, as it should be done but I am not fast enough so what I have done is adjust them cold then I warm the engine and check for the hot specs. Adjusting the valves is not hard, it can actually be sort of fun if you are in the mood. eachl lobe should point up when you check clearance. use a remote starter to make life easer. Also it will be a good time to visualy inspect the valve train.

Also do not be alarmed if the rockers seem to be loose when there respective lobe is up, this is normal.

Yeah, i figured that spring isn't suppose to be there.. I was planning to adjust the valves cold, since i know for a fact i'd work pretty slow ha. Okay i think i feel a little more comfortable doing it now. With the remote start, from what i've been reading people say it turns over a little bit too quick?

Here's a video of the car i took the other day when it was having a "fast idle"

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Just to check in so far what i've done. Had valves adjusted, timing set, CO % at idle adjusted to about .70% had someone put a gas analyzer on it while adjusting the AFM bypass screw, i mean the car runs damn good now (well to me at least) doesn't reek of fuel idling as bad as before, EGR replaced. Took the car to get smogged again and it still failed! Only the HC's seemed like it lowered compared to last results went from 400ish to around 220 at 15mph and 25mph, still it's not the max emissions, for HC it's like 180ish.. the CO were 6% at 15mph and 25mph max is 1.36%. Went through the fuel injection bible again with the help of a member here on the forum. Did the tests for CO too high poor gas mileage, everything checks out OK, only thing that's off a little is the AFM tests they're about 20-30 ohms off. I doubt that'd have that big of a difference for the CO% to be so dang high? Tested the TPS aswell and i think i was doing it right.. for pins 3-18 at ECU connector the part throttle is that like "barely" moved? It says it should show no continuity. When i have the throttle depressed about hallways from the throttle body linkage (Pushing down) it shows continuity as it says it should for (WOT) but wouldn't it be the other way around? Throttle depressed half ways no continuity, throttle depressed ALL the way continuity? I'm pretty much stuck. Only other possible components i can think of is a leaking injector causing to pour too much fuel when car is in motion?

Edited by Samson

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I've also measured the AFM: i referred to the EFI bible pages (49-51) Okay, the measurement #1 was pins 6 & 8 now this was from the ECU plug( All three measurements were) which was 321 Ohms the EFI bible says measurement should be at approxiamtely 180 Ohms so.. that is definately not righ?, measurement #2 which is pins 7 & 8 257 Ohms EFI states should read (Continuity, small resistance) measurement #3 Pins 8-9 measured 145 Ohms EFI bable states should read approximately 100 Ohms. I haven't actually measured from the AFM itself but i did clean out the flap which Air flow Meter Cleaner.

These numbers are more then 20-30 ohms off. Looks like 40 and 45 off. I'm not positive but I think that it's the ratio between the two numbers that matters most since it's a voltage splitting device. I think that the ECU uses the ratio between what goes out and what comes back to determine where the AFM vane is. The spec. ratio is 1.8 (180/100), your ratio is 2.2 (321/145).

What is the number on your AFM? The guy that put the big throttle body on might have also installed the wrong AFM. Should be A31-060-001 I believe.

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These numbers are more then 20-30 ohms off. Looks like 40 and 45 off. I'm not positive but I think that it's the ratio between the two numbers that matters most since it's a voltage splitting device. I think that the ECU uses the ratio between what goes out and what comes back to determine where the AFM vane is. The spec. ratio is 1.8 (180/100), your ratio is 2.2 (321/145).

What is the number on your AFM? The guy that put the big throttle body on might have also installed the wrong AFM. Should be A31-060-001 I believe.

Oops, sorry should've noted it i purchased another Reman AFM from a member on a forum it looks relatively new here are the numbers i got when i tested this AFM. From pins 6-8 i got 214, pins 7-8 i got 204 ohms pins 8-9 i got 126 ohms. Is it possible that the wiring is bad? May need new re wiring? So now it's 214/126. Also measured the Air temp sensor and it was 1514 ohms had engine warmed up for about 10 mins and the engine temp was about 100 degrees somewhere in that range. But this is measured from ambient air temperature? It was about 50 degrees Fahrenheit specs says should be 3.25 - 4.15

Product # on my AFM now is MF20090

EDIT: Checked if the CSV was leaking too, removed it from manifold started car no drips, nothing was dripping or spraying out.

Edited by Samson

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Kind of confusing, I went back and see in Post #9 that you had measured 180 and 100 with the AFM removed. Was that the replacement AFM or the old one? Now you're at 204 and 126. Is that the connector or at the AFM? Post #9 suggested that your AFM was fine but that you had bad wiring connectins.

For the temperature sensors higher resistance adds fuel. The spec. from the FSM is actually 3.25 kOhms to 4.15 KOhms, so your 1.5 kOhms is actually reading a little lean. If the leanness isn't causing a miss then it shouldn't hurt the emissions. A lean miss can hurt emissions though.

The TPS is just a three position switch that tells the ECU if the throttle is at idle, mid-range or open. The continuity measurements need to match exactly what the FSM calls for. More fuel is added at idle and at open throttle. In the middle the ECU uses the AFM. Your failing the test at the mid-range so the TPS could be the problem.

Did the PO do any other "mods" like a different camshaft or bigger injectors? The "big-throat" throttle body doesn't add much without them. You might check the other engine parts to see if they are stock. I think that FastWoman was right and you'll just have to keep fixing the PO's "upgrades". Looks like you're making progress though.

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Kind of confusing, I went back and see in Post #9 that you had measured 180 and 100 with the AFM removed. Was that the replacement AFM or the old one? Now you're at 204 and 126. Is that the connector or at the AFM? Post #9 suggested that your AFM was fine but that you had bad wiring connectins.

For the temperature sensors higher resistance adds fuel. The spec. from the FSM is actually 3.25 kOhms to 4.15 KOhms, so your 1.5 kOhms is actually reading a little lean. If the leanness isn't causing a miss then it shouldn't hurt the emissions. A lean miss can hurt emissions though.

The TPS is just a three position switch that tells the ECU if the throttle is at idle, mid-range or open. The continuity measurements need to match exactly what the FSM calls for. More fuel is added at idle and at open throttle. In the middle the ECU uses the AFM. Your failing the test at the mid-range so the TPS could be the problem.

Did the PO do any other "mods" like a different camshaft or bigger injectors? The "big-throat" throttle body doesn't add much without them. You might check the other engine parts to see if they are stock. I think that FastWoman was right and you'll just have to keep fixing the PO's "upgrades". Looks like you're making progress though.

Yes, that was the old AFM when i purchased the vehicle that it was installed already everything from post #19 to now is what the vehicle has installed now or whats been done so far. Now that i think of it my AFM connector is cruddy and old there was alot of corrosion on the terminals when i first removed it to swap the AFM i have installed now. I sprayed electrical contact cleaner and cleaned it as best as i could've.

From looking at my recent smog results at 15mph it was 270 and 279 at mph. Maximum is 214 @ 15, and 181 at 25. It is indicating a low-key lean mixture or small misfire but with the CO so high in the 6% range that's also whats making it shoot so high, no? I could be wrong.

Reviewed the FSM again and it just says when testing pins 3, 18 put the pedal to the floor and should show continuity, same thing if i were to do it from the throttle body right? In that case it is showing continuity.

No other mods, when i have valve cover removed its stock cam shaft, one thing i did notice on the intake valve #1 the cam lobe was like gouged right at the corner i wouldnt say a massive chunk was missing but it was about a half an inch knick not in the middle of the lobe but right at the edge i should've got a picture but i totally forgot. Another "mod" the PO did was rewired the whole FI system. It's not pretty. There's tons of excess wires, but the other tests i was doing that the fuel injection bible stated for High CO were checking out OK. Except for AFM from results posted above and the TPS which i'm iffy about. Is it possible how the Fuel injectors are wired to be stuck open? I did the measurements were the voltage checks and #1-#6 all showed battery voltage.

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I think that your HC numbers are pretty close. Small changes will probably get you there. Do you have the vacuum hose connected to your fuel pressure regulator and does the FPR work correctly? Fuel pressure should be ~36 psi with the hose disconnected and 28-32 psi with it connected, at idle.

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I think that your HC numbers are pretty close. Small changes will probably get you there. Do you have the vacuum hose connected to your fuel pressure regulator and does the FPR work correctly? Fuel pressure should be ~36 psi with the hose disconnected and 28-32 psi with it connected, at idle.

I have a gauge hooked up inline with the filter it shows a about 32psi at idle. What do you mean by vacuum hosted connected to FPR? The hose from FPR is going into the intake manifold, yes.

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Samson, did you get your car to pass smog and what kind of numbers did it post?

Hey Denis, nope.. still haven't gotten a call from the shop. Still waiting..

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I have a gauge hooked up inline with the filter it shows a about 32psi at idle. What do you mean by vacuum hosted connected to FPR? The hose from FPR is going into the intake manifold, yes.

Hi Samson,

Just a quick run down on how the fuel pressure works.

The fuel pressure regulator controls fuel pressure by reading the vacuum. That way the injectors always have the right differential pressure over the nozzles. Eg: At idle you have high vacuum and therfore you need lower fuel pressure, at full throttle / full load you have very little vacuum and therefore higher pressure in the fuel system. The system wants to maintain around 35 psi across the injector nozzles.

The ecu works on a time basis pulsing the injectors. A higher differential pressure will give more fuel, but the ecu cant calulate this because it doesnt read the fuel and vacuum pressure.

Thats why you do an initial test with vacuum hose disconnected or turn ignition on and open the afm via the aircleaner the simulate air flow. The pump will then run and should read around 36 psi.

Chas

Edited by EuroDat

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Hi Samson,

Just a quick run down on how the fuel pressure works.

The fuel pressure regulator controls fuel pressure by reading the vacuum. That way the injectors always have the right differential pressure over the nozzles. Eg: At idle you have high vacuum and therfore you need lower fuel pressure, at full throttle / full load you have very little vacuum and therefore higher pressure in the fuel system. The system wants to maintain around 35 psi across the injector nozzles.

The ecu works on a time basis pulsing the injectors. A higher differential pressure will give more fuel, but the ecu cant calulate this because it doesnt read the fuel and vacuum pressure.

Thats why you do an initial test with vacuum hose disconnected or turn ignition on and open the afm via the aircleaner the simulate air flow. The pump will then run and should read around 36 psi.

Chas

This makes so much sense. Thank-You. Now, the FPR is also a possibility that it's adding more fuel at high engine load thus giving me a rich mixture? I was going to get an adjustable FPR (have it set at 36 psi?) and change the fuel rail to an aftermarket unit. Can't do any other tests now since i took the Z into the shop.. Denatured alcohol also came up when i was talking to some friends about having the Z pass smog, they say get the car to about 1/4 of a tank and pour a gallon of the alky in there and should pass with flying colors just pump full tank after the test to dillute the alcohol ..but idk.

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I did this http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html to my '77 instead of the adjustable fuel pressure regulator and it fixed my problem. ZedHead suggested putting it inside the car for adjusting while driving and that worked out really good. My mechanic friend kept my car for 4 weeks and couldn't figure out the problem, ZedHead and Fastwoman got it in 5 minutes. He clamped off the return line to increase fuel pressure in the system and thought raising the pressure to 45lbs would fix the stumble. $5 from Radio Shack and it runs better than ever now.

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Hi again,

Like Stieunseen mentioned in post #42. The resistor tweak in the temp sensor loop is a great way to adjust the fuel air ratio on the OEM efi.

Some people play with the spring in the AFM to richen the mixture. It works well a low to medium air flows but leans out when the flap fully opens too early and you haven't reached full throttle.

Unfortunately your problem is a rich mixture and the resistor tweak is to compensate a lean mixture. THe injector open time decreases as the resistance decreases. Therefore if you increase resistance you will increase injection time and richen the mixture.

You will need to find the problem first and then use this mod to fine tune your mixture to pass smog.

Chas

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Hi again,

Like Stieunseen mentioned in post #42. The resistor tweak in the temp sensor loop is a great way to adjust the fuel air ratio on the OEM efi.

Some people play with the spring in the AFM to richen the mixture. It works well a low to medium air flows but leans out when the flap fully opens too early and you haven't reached full throttle.

Unfortunately your problem is a rich mixture and the resistor tweak is to compensate a lean mixture. THe injector open time decreases as the resistance decreases. Therefore if you increase resistance you will increase injection time and richen the mixture.

You will need to find the problem first and then use this mod to fine tune your mixture to pass smog.

Chas

Okay, Just got done talking with the shop and he said that the computer is shorted, said it was showing 12volts on both sides of the computer? Didn't really understand him.. He told me to not throw a computer in there till I redo the EFI wiring. He's not going to charge me either for Diagnostic and told me to just come pick it up..

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How are you going with the computer? Im not sure what your mechanic meant by "12volts on both sides of the computer" ?

Have you done the tests in the FSM and Trouble Shooting manuals?

http://www.xenons30.com/reference.html

http://www.xenons30.com/files/280zfuelinjectionbook.pdf

Chas

At the injector connectors on both pins it showed power when It's suppose to be power and ground, correct? Therefore its shorted somewhere in my wiring? I've noticed that my computer is also a A11-601 which is off a 78 if I'm not mistaken.. 77s should have A11-600?

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My computer is an A11-601-000 with Lot nr. 7511 for a L28. The car is from 5/77 and as far as I know the unit is original.

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Coincidentally, today I was looking at a few ECU's I've collected to see if they had the "altitude compensation" pins. All of them are A11-600-000 and they come from cars from 76-78. While checking the FSM's I saw that only the California cars came with altitude compensation. I wonder if the -601- ECU's have the altitude compensation circuit? Samson is in CA, Eurodat, where did your car, or ECU, come from?

The switch is described and shown in the Engine Fuel chapter, it drops the fuel supply through the injector duration by 6% when the switch closes due to low pressure from high altitude. It wouldn't affect operation unless the switch was shorted, causing a lean condition.

Samson, your mechanic doesn't understand how the injection system works. The injector connections have 12 volts on both sides due to the way the transistors operate (I confess that I'm not clear on why that is either, but it is). The injector solenoids don't activate until current actually flows when the transistor circuit allows it to. 12 volts on both sides is good.

As I said in an earlier post, you're pretty close. I had to adjust my idle air screw and install some new plug wires on my last DEQ (our emissions checkers) visit here in Oregon. A miss will spew unburned fuel (bad), and the idle air screw can lean up the idle. I wouldn't do anything major and I would find a mechanic who knows old EFI.

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At the injector connectors on both pins it showed power when It's suppose to be power and ground, correct? Therefore its shorted somewhere in my wiring?

No. Measuring +12 volts on both sides of an injector is not necessarily a problem. The way the system works is this...

One side of each injector is always connected to +12 through a "dropping resistor". You should always measure about +12 on that side of the injector.

The other side of each injector is connected to the ECU. Inside is the ECU is a switch (a transistor) which, when closed, connects that side of the injector to ground.

When the transistor switch is open, no current flows through the injector and you will measure +12 on both sides of the injector. When the transistor switch is closed, current flows through the injector (which causes the injector to open), and you will measure +12 on one side of the injector, and ground on the other.

However... The amount of time that the transistor switch is closed is very short, and your typical voltmeter will not pick it up. Your typical voltmeter will average the signal in some way, and since the amount of time that the injector is connected to ground is such a small amount of time, it will essentially average out to +12.

Does that help? Does that make any sense?

I'm not sure that your mechanic is familiar with fuel injected systems.

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Coincidentally, today I was looking at a few ECU's I've collected to see if they had the "altitude compensation" pins. All of them are A11-600-000 and they come from cars from 76-78. While checking the FSM's I saw that only the California cars came with altitude compensation. I wonder if the -601- ECU's have the altitude compensation circuit? Samson is in CA, Eurodat, where did your car, or ECU, come from?

The switch is described and shown in the Engine Fuel chapter, it drops the fuel supply through the injector duration by 6% when the switch closes due to low pressure from high altitude. It wouldn't affect operation unless the switch was shorted, causing a lean condition.

Samson, your mechanic doesn't understand how the injection system works. The injector connections have 12 volts on both sides due to the way the transistors operate (I confess that I'm not clear on why that is either, but it is). The injector solenoids don't activate until current actually flows when the transistor circuit allows it to. 12 volts on both sides is good.

As I said in an earlier post, you're pretty close. I had to adjust my idle air screw and install some new plug wires on my last DEQ (our emissions checkers) visit here in Oregon. A miss will spew unburned fuel (bad), and the idle air screw can lean up the idle. I wouldn't do anything major and I would find a mechanic who knows old EFI.

My 77 is a NON-CA car therefore there is no altitude switch aswell as a catalytic converter.

I now understand what you all mean thanks for the enlightment.

Also went over the car today and noticed that the vacuum routing for charcoal canister dist vac port aswell as the ported vacuum switch were hooked up wrong.. from the charcoal canister it went straight to the nipple under my throttle body. Then goes Vac advance>port vacuum switch>other nipple of vacuum switch goes to this "thing" next to the egr sorry I don't know what It's called.. could this affect the mixture?

Edited by Samson

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