Water Thermo Sensor 13b

[mbuskuhl]

Do I need this functioning? The connector is old and tired and the sensor has a terminal about broken off. Not even sure if it is functioning but when I pulled my front cover today (and water pump) it got even more jacked up. Was hoping it wasn't really that important, I am running a stock ECU still if that matters.

 

[mbuskuhl]

Hmmm... 56 views and no one knows? After some more research I'm going go with yes, the thermo sensor is necessary as it plays a big role in regulating the fuel mixture based on water temps.

 

[Weaver7]

Mark take a look at the 2nd Gen Erractic performance thread. I asked the same questions and yes it does I believe you are referring to the unit that screws into the back of the water pump correct?

Bill Weaver
ITS RX7 #63

 

[C. Ludwig]

I'm going go with yes, the thermo sensor is necessary as it plays a big role in regulating the fuel mixture based on water temps.

Correct.

 

[Chris Wire]

After some more research I'm going go with yes, the thermo sensor is necessary as it plays a big role in regulating the fuel mixture based on water temps.

Might this also be the source of another problem I'm having? Below 3500 rpm, the engine runs very rough, but revs up with no hesitation, it just acts like it's breaking up. Once 3500 is reached, it smooths right out and revs great, but the header is glowing above 4000 rpm if the throttle is held open.

My initial research points to a wiring harness problem with the primary injectors, but before I spend time and energy pulling the upper/middle intakes off, I thought I would just hijack this thread ( ) and run it buy you guys!
Injectors are all new, so I've ruled those out. So that leaves, thermo sensor or harness?

 

[NCRX7RACER]

The water thermo sensor does affect the mixture. The computer looks for normal water temp here. Some people looking for a cheap way to richen their mixture put an inline potentiometer in the wiring.



On Chris's breaking up problem, check the throttle position sensor. It only measures the first 20% or so of throttle before its goes into wide open throttle ecu mode. Do you have 1 (86-88) or 2 tps ( 89 up)? Make sure the wot ohm reading is correct.

Check all your grounds on the wiring harness including the one to the firewall.

There are some bad new aftermarket injectors around. Are your injectors mazda factory?

 

[Chris Wire]

S5 electronics
new s5 rebuild
new turbo fuel pump
newly reconditioned fuel tank
new fuel filter
new reconditioned injectors from ISC Racing - flowed and balanced
new Aeromotive FPR set at 30psi w/ vacuum reference to manifold

All items above newly installed since last year. Car idles a bit rough until it warms up then it's very smooth. Starts fine hot or cold.

The kicker for me was the 3500 rpm threshold where the characteristics of the engine changed dramatically.

I realize I may already have it diagnosed, just looking for 2nd opinions.

 

[seckerich]

Your fuel pressure sounds low given a stock 89-91 computer. These are notorious for running too rich stock. Hard to get enough top end fuel to an 86-88 and hard to take it out of a 89-91. My guess is you are running so low to get top end right that you are way off at low RPM. Have you tried more pressure? Check that the restrictor is still in the line to the map sensor. What AFR reading do you get at WOT on a dyno? Glowing header is usually lean or stupid rich.

 

[Chris Wire]

Your fuel pressure sounds low given a stock 89-91 computer. These are notorious for running too rich stock. Hard to get enough top end fuel to an 86-88 and hard to take it out of a 89-91. My guess is you are running so low to get top end right that you are way off at low RPM. Have you tried more pressure? Check that the restrictor is still in the line to the map sensor. What AFR reading do you get at WOT on a dyno? Glowing header is usually lean or stupid rich.

Dyno?? No dyno yet. Still spending money to get the rest of the little things done to make it track worthy. I was going to take it to the Daytona Dyno at the SARRC in 3 weeks, but with a glowing header I'm not so inclined to do that right now, given the current circumstances.

Does anyone have any tricks to getting the car to run with the upper manifolds off? I figure if I keep as much hooked up as possible, and prop open the AFM, I should at least be able to fool the car into thinking its all together. I'd like to be able to play with the primary injectors and the wiring harness while its running. Any other suggestions?

 

[Eagle7]

Buy a wideband AFR meter. Put a bung in each header tube.

I assume you know that 3500 RPM is about where the secondary injectors kick in.

 

[Chris Wire]

Your fuel pressure sounds low given a stock 89-91 computer. These are notorious for running too rich stock. Hard to get enough top end fuel to an 86-88 and hard to take it out of a 89-91. My guess is you are running so low to get top end right that you are way off at low RPM. Have you tried more pressure? Check that the restrictor is still in the line to the map sensor. What AFR reading do you get at WOT on a dyno? Glowing header is usually lean or stupid rich.

Well I tried the fuel pressure route last night to no avail. Idle held around 2500 rpm, I ran the pressure up and down between 28 and 40 psi. The engine note changed a bit but it had no effect on the roughness of the engine running. I guess I'll double check the TPS this evening and see how that goes.

Curious that there is nothing in the vacuum line from the engine to the MAP sensor as Steve suggested, what might that do? I could find no reference in the factory manual to any such restrictor.

Marty, I am aware that the secondaries kick in at 3500, as I said, I'm just fishing for more info on possible causes. I'm pretty much resigned that I'm going to have to pull the upper intakes off at this point.

 

[jrx13]

Just curious....are you still running the air pump or did you eliminate it? How about the air control valve? I have seen stuck air control valves directing all the air from the air pump into the exhaust causing it to glow red hot.

 

[NCRX7RACER]

The restrictor or pill as some call it is just a pea sized piece of plastic with a very small (almost needle like) opening in it. It is usually in the line close to the pressure sensor. Try mashing the line to see if you can feel it in there. I think it dampens the sudden pulses in the intake runners.

 

[mbuskuhl]

Hmmm... 56 views and no one knows? After some more research I'm going go with yes, the thermo sensor is necessary as it plays a big role in regulating the fuel mixture based on water temps.

Talk about some thread hijacking here ... Anyways, I replaced my thermo sensor with a new one from Mazda and got the car back together. Bill, yes this is the one on the back of the water pump housing. It idles a little different and almost died a few times, but did rev fine, so I'm thinking I had tuned the car previously to a bad sensor? Perhaps the fuel mixture is all jacked up now that the sensor works, after all 32 PSI fuel pressure has gotten me a 13.6 AFR and some good HP...yes, the injectors are stock NA injectors. An engine builder helped me and stabbed the CAS so timing should not be an issue. Back to the dyno to check my AFR and make sure there is still power. Maybe I'll just buy an AFR gauge one day but only the dyno can confirm I still got HP!

 

[Chris Wire]

Just curious....are you still running the air pump or did you eliminate it? How about the air control valve? I have seen stuck air control valves directing all the air from the air pump into the exhaust causing it to glow red hot.

Gone.

Sorry Mark!

 

[tdw6974]

"I was going to take it to the Daytona Dyno at the SARRC in 3 weeks, but with a glowing header" Hmmm Vacummn leak? Have you tried the spray trick to see if you got a leak near back of intake manifold? How about interference between rear housing an plenum that keeps from sealing? TW

 

[mbuskuhl]

Gone.

Sorry Mark!

I was joking earlier and wanted to pop back into the discussion. Any talk on these motors can only help!

 

[Chris Wire]

Check that the restrictor is still in the line to the map sensor.

Yep, still there.

On Chris's breaking up problem, check the throttle position sensor. It only measures the first 20% or so of throttle before its goes into wide open throttle ecu mode. Do you have 1 (86-88) or 2 tps ( 89 up)? Make sure the wot ohm reading is correct.

Checked TPS per manual. Narrow range measurement (A/B ) shows .91 at idle, and 4.51 at WOT (both within normal range), however when I measured the full range sensor it seemed to be all over the map, with the idle measurement way too low and the WOT measurement way too high. Does this mean its bad, or just that I'm an idiot? The FSM says there is no way or reason to adjust the full range part of the TPS as its controlled by the ECU, and I don't have a spare to just change it out to check it.

Going back to basics, I also checked the following:
- rechecked the CAS, all looks well.
- checked all grounds, found the one on top of the motor under the intake to be loose, so I fixed that.
- pulled the upper intake and all the wiring to the primary injectors, including the connectors, looks fine. Have not yet checked continuity with the primary injector wiring yet.
- intake air temp sensor terminal broken off. Could that be a factor?

Still need to double check for a vacuum leak, and maybe I'll do the FSM test on the water temp sensor.

 

[Eagle7]

- intake air temp sensor terminal broken off. Could that be a factor?

Sure could. Air temp (= density) determines the amount of fuel to provide.

Still need to double check for a vacuum leak, and maybe I'll do the FSM test on the water temp sensor.

You said this is a fresh rebuild. Any chance you've got an S4 rear iron? That would interfere with the S5 intake and cause a big vacuum leak.

 

[Chris Wire]

You said this is a fresh rebuild. Any chance you've got an S4 rear iron? That would interfere with the S5 intake and cause a big vacuum leak.

I suppose its possible, as I don't know the origin of the core it was rebuilt from. Is there a easy way to identify between the two?

Just fired it up again, and brought it up to temp slowly. Same conditions are present and the idle was a bit lower due to the TPS adjustment I think. Slight stumble now on throttle tip-in that wasn't there before, but its not bad and I could live with it.

Also measured O2 sensor that should be 0-.4v at idle (it is) and .5-1.0v under acceleration (it isn't). Mine measured .21 at idle, .32 under acceleration, and .59 or so under deceleration. It's backwards according to the manual, but I think that it may be reacting to the poor mixture situation I'm already dealing with.

I think I'm going to pass on Daytona and just replace the the terrible trio - water temp sensor, TPS, and O2 sensor. They were all carryovers from the previous engine, which didn't run when I bought the car, so I guess I should just bite the bullet.

That and a wideband setup might get me everything I need in time for Labor Day at Sebring. Can anyone recommend a decent quality, yet relatively inexpensive wideband setup? I don't do any data logging at present so I just need a bare bones deal.