I have been racking my drain dealing with a no start issue. The car would start and idle/rev without issues last week, it sat while I was at work and now will not start.

1994 1.8 with a modified FMII kit
FIC 650s
Mslabs MS3 basic with innovative LC2
Toyota COP with capacitors

When I bought the car the previous owner had installed a rats nest of wiring to run a VCR/PS1 and intricate Alpine alarm. I removed all of the wiring section by section, testing the cars function each time in hopes of avoiding this issue. After it ran fine on the linkECU, I pulled that and installed the MS3/injectors/coils. The car started and idled fine, AFR ect all within spec. I was getting ready to road tune the car prior to a dyno tune and now I have a no start issue. The car cranks, but will no longer start. A quick rundown of my trouble shooting;

-Followed miata no start guide (No-Start Troubleshooting Guide - MX-5 Miata Forum)
-Pull each of the coils, there is spark
-Swapped the CAS with another one of my 1.8 cars, works fine on other car, new CAS has no change on the 94
-All fuses check out visually and with a voltmeter
-Battery 12.87 volts, have it on a trickle charger during trouble shooting
-Main EFI relay clicks when connected, swapped with a known good relay, no change
-Noid light hooked up to injector wires, does not flash or light at all when cranking. 12v to each connector, continuity at ECU pins for each injector
-No fuel spraying when cranking, cylinders/plugs dry, rail and injectors pulled and spray no fuel when cranking
-Checked continuity/resistance on wires to ECU; CAS, Coils, injectors and all grounds except (2D sensor ground main) check out.
-Threw a tone generator on the 2D pin, I am able to get tone at the TPS, O2 sensor, CAS, MAF, EGR and engine coolant temp sensor
-Hooked up laptop to the ECU and noticed that the TPS is maxed at 137%, attempted to calibrate TPS and the value will not change from 1020 no matter where the throttle is.

All of this makes me think there is a grounding issue causing the no start, but I cant find it. I cleaned and inspected all three grounding points (driver rear, passenger intake manifold, pad below throttle body.)
I assume that the black/blue wire runs from the ecu into the engine bay and to the various sensors. I get tone down the entire harness following that route, but I have yet to pull the shroud and visually inspect. I am trying to avoid pulling the dash.

Does the black/blue ground wire split off somewhere else? Does anyone else have any ideas?

 

tune your car.

 

Nothing changed between it running last week and not running this week? Did you mess with anything?

With the laptop hooked up is tunerstudio reading a tach signal when the car is cranking?

When you turn the key to the "on" position do you hear the fuel pump run?

 

Yes, fuel pump primes and I have pressure at the rail. Yes the laptop reads a tach signal.
The car sat in my shop for 6 days. I didn't work on it at all.

Braineack, usually when you post a smart *** answer, it is because a person has asked a dumb question with little research. I am not sure that is the case with my post.

I am wondering if the Blk/blu wire goes elsewhere other than into the bay.

 

you installed a MS3. tune it so it starts and runs.

 

Stab you in the neck lol. Yes I may be a newb on this forum, but I have experience on other platforms and ECU setups (hptuners, EFIlive, AEM, ect). On a side note, at one time it was tuned for maximum idle power. I think I made 22 hp.

 

next time NOS at idle.

 

I only do that on the dyno for mad tyte dyno numbers or explosions. Either way it awesome

 

This is your problem. Sounds to me like the reference is going to the signal wire, maybe the sensor is wired wrong or there's a wiring problem between the sensor and the ECU. Or TPS is not installed to throttle body correctly.

If it won't calibrate, then you have a bad sensor or a wiring problem. TPS values that are really high put the engine in flood-clear mode (no injector pulse width as you have described/tested). Fix the TPS problem and it will then add fuel.

 

flood clear engaged.

 

Update:

Could not find the short in wiring to the tps. The previous owner had installed various vampire taps through out the harness, so I pulled the entire engine harness and ECU to main harness and installed a new one from a parts car.

Now I get communication with the TPS, but the range is only 960 to 1120. Also while just sitting the TPS is erratic jumping from 0.1% to 1.8%. I still have no injector response, so I installed the factory ECU. With that all 4 injectors are working, using a noid light to verify. Obviously car still doesn't start as I have no maf and no factory o2 sensor.

Suggestions?

 

My guess is you should post some data, like logs, msq, things like that so someone can take a look.

Also not sure but can a TPS be installed wrong on a miata? On some car it will have a hug dead spot and very little range if you "miss" the groove when you snap it in. Most newer cars it only goes in one way though so you can't mess it up.

If TPS in Tunerstudio shows a low % value it should be firing the injectors. Again, post a log of you trying to start the car, post screenshots too that shows this that have RPM, map, TPS, injector duty cycle, injector PW, things like that relevant to your problems.

 

Disconnect the TPS.

Check if you get 5V on any of the wires.

Check if any of the wires is a ground.

Check of the signal wire has good continuity all the way back to the ECU.

Then finally check the TPS itself, maybe swap it with a good one?

 

Patmx5, I will post up my msq file as well as some screen shots when I get home. TPS was never removed, but I will source another just in case it failed per Dimitri's advice

Thanks Dimitri, disregard the email I sent you. It is basically a replica of this thread.
I have ground on the sensor ground wire (black w/ blue stripe) and 4.92v on the red wire. I need to have my wife help me with the signal wire, arms aren't long enough.

 

Continuity confirmed between tps and ecu side of harness on both the input and ground.

 

Did you measure the TPS values with the DVM and confirm whether or not it's working as expected?

--Ian

 

I did and noticed that it was slight out of spec testing AB when throttle was closed and fully open.

Spec 3.82 down to .52
Mine 3.2 down to .8

I am pulling a working TPS off of one of my other cars and I will report back

 

And so the saga continues. Replaced the TPS with a new sensor, same problem. Megatune still shows a maxed out, unresponsive to actual throttle postion tps value of 132% (that valve actually rapidly fluctuates between 132% and 135%) . Unplug the TPS and the signal drops to zero.

Probing the TPS connector shows 4.92v on the red wire, nothing on the middle two and 4.92v on the blk/blue sensor ground wire. The funny thing is, I have continuity between that wire and ground. I then checked all the other sensors that use the ECU sensor ground and same thing, continuity to ground, but a reading of 4.92v.

I then hooked up the stock ECU and rechecked. The wiring now shows no voltage to ground on any of the sensors that get ground from the ECU (tps, o2 sensor, egr, cas), and continuity to ground. Remember, I am able to get response from the injectors with the stock ECU, but nothing with the megasquirt. Granted the car won't start with the stock ECU as there is no o2 sensor or MAF sensor

Does this mean that there is an issue with my megasquirt ECU ground?

 

Check the build threads, i was reading through them and someone also had a similar issue that you are having with the TPS. I believe it was ERAT or BoostedSmurf, check out their builds it should be on one of the first few pages.

If you are looking to get the car running maybe try to just run full on the MAP sensor and ignore the TPS until you get your car sorted. You can always figure out the TPS once you get the car running.
Just my 2 pennies