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I was testing my MAP sensor this morning to see if it was possibly contributing to my FD not starting using the procedures in the FSM and in this post https://www.rx7club.com/3rd-generati...8/#post3763007 and found some confusing results. I built some small jumper wires with connectors to place in between the harness and the sensor so I could get my meter onto the pins while the power was applied to the sensor. The first time I measured reference voltage between the BR/W wire and a ground, I found that it was ~4.91v, however now when I attempt to measure the same, I see 0v. I also tested a different BR/W connection on the TPS and found that it had a good reference voltage, so I'm not sure what exactly happened. Did I fry something while testing?
Also, before the reference voltage was gone, I also measured 0v between the reference ground (B/LG) and signal (G/Y). Is this a dead MAP sensor as well?
I don't think I've ever seen a bad MAP sensor. They're pretty hardy. That said I am concerned with hooking up jumper wires to test, you could have shorted the 5v rail.
Stock ECU. The FSM shows probes being inserted in the back of the connector, but mine is far too cooked for that. If the 5v rail is fried, wouldn't the measurement on BR/W at the TPS also be 0v since they're connected?
Also, the jumpers I made were less random wire and more harness extension, specifically to avoid shorting things. I suppose I could have accidentally touched the wrong pin when testing with the meter
OK, I think you're at the point where you need to give us a breakdown of what's going on. You had the fuel pump thread and now this one - we need a more complete picture of everything to get your car running.
Was it working fine then stopped? New engine? Mods on car? What have you changed since it was last running?
Also, with regards to the point of this post, you can pull the connector off the MAP sensor and check the 5v wire - you don't have to do a jumper wire or anything. If it's getting 5v and the other wires aren't damaged you should be good.
I needed to check the voltage between the signal and reference ground, which was the original reason to build the jumpers. It was also seeing 0v on the signal wire which was the cause for more investigation.
I'll type up a more thorough background on the car here in a sec.
I sincerely appreciate the help, I'll try to keep it as brief as possible since I didn't intend to drown anyone with a build thread. The car was originally purchased running with almost 200k miles and a blown coolant seal, suspension issues, and other engine issues from an owner who didn't want to fix all of the issues with the car. At the time, this wasn't a problem since it was going to be a shell for my 20b, however after a move to a jurisdiction that really isn't going to allow that, I have decided to put it back together with mostly stock components. The car mostly sat in storage from 2015 with the original motor removed but not rebuilt until I pulled it out to start on last fall. The shell did not undergo modification for the 20b, so it was effectively still the same car in more deteriorated shape than when I got it. I swapped the rest of the long block components to a new Mazda OEM 13BREW crate engine, replacing ones that failed during individual testing and replacing other supporting components as I notice they've failed. A lot of them have failed, so a lot has changed since the car last ran.
For engine/power components themselves:
new OEM short block, OEM gasket set
99 spec twins from the previous engine
ECU is stock
full silicone vacuum replacement without any deletes
full replacement of emissions and turbo control solenoids (literally none of these worked)
replacement of cracked plastic parts (primary turbo elbow, pressure/vac chambers, probably more I'm forgetting)
new OEM engine harness
new FC thermoswitch, new O2 sensor
new OEM plugs
TRUST Air NX intake installed by previous owner
Bonez turbo back exhaust w/ cat installed by previous owner
Split air blockoff plate on the LIM, but otherwise the emissions are intact
For the fuel system:
primary and secondary injectors were sent out for a rebuild and flow test. All came back as working well, however the primaries leaked through the electrical connector when installed. Replaced with new OEM
new OEM FPD installed and new OEM FPR on the way due to the results from the other thread
new OEM updated fuel tank (previous was a rust mess)
new Walbro 255
new OEM fuel filter
For electrical stuff that is relevant:
The car had at least one additional large ground wire run from the battery negative clamp to the block, which I did not reconnect yet
I didn't see any other mods for a security system, fuel pump rewire, changes to the stock stereo, or anything else
Other stuff that probably isn't relevant:
New Koyo
AC removed
PS removed with welded quill
A bunch of suspension work (pillow *****, TIEN coilovers, replaced worn tie rods)
Full new set of maintenance items (belts, oem thermostat, oem oil filter, AST/pump caps)
Full new fluids
New 51R battery in the stock place with a TurboJeff tray
Broken ebrake cable replaced
New clutch master/slave (previous was non-functional)
New brake master rebuild kit (previous did not hold any pressure)
Stuff I know is currently also wrong:
Ignition sub harness connectors are disintegrating, I have a new one on order
Both trailing coils do not fire during cranking, but leadings fire. This was tested with a timing light, but not with visible sparks. Not sure the cause, might be the harness, spark was next on the list
Tach is dead, but sometimes goes haywire so I presume I have a questionable ECU ground
At least one relay under the dash that clicks intermittently
Passenger headlight does not come up, however both lights turn on and driver's side raises
Blown passenger engine mount - I have replacements that aren't installed
Anything else not listed you can assume is swapped from the old engine or not removed/modified. The old owner was a regular customer of Rotary Performance in Dallas and they did a fair bit of work, including the previous rebuild and 99 spec twin swap, so the mod work isn't shoddy, just old and cooked.
The first time I tried to start the engine after solving the injector issue (but before the rail pressure issue) I could smell fuel in the tailpipe and on the plugs. After reseating the fuel pump and performing the line pressure tests, everything in my garage smells like fuel so it's hard to tell on subsequent start attempts. I've performed the deflooding procedure and can hear strong puffs during the compression strokes. I can see liquid on the plugs after an attempt, which could be OMP oil or fuel or both. The timing light indicates both leading wires are seeing the firing event and L1 is manually traced to the front rotor leading hole, L2 to the rear leading hole. All the plugs have the right OEM plug installed and torqued. I did not function check the primary injectors before I installed them and I really really hope that's not the issue.
Thanks for that! It makes it a lot easier to help with some diagnosis. Sounds like you're really trying to use the right parts and do it the right way which I appreciate, that's definitely the way to go.
Are your primary injectors new or used/cleaned at this point? You only need the primaries to start and idle. If they are cleaned there have been cases where they will stick after sitting a while after the cleaning. Typically you can squirt some penetrant on the tip of the injector and then hook 12v and ground to the 2 pins and tap the ground wire a few times to get the injector to move. Cycle it a few times and get that penetrant in there. Even if they are new, that could also be the case - they've probably been sitting on a shelf for ages. You may be able to just do 12v/ground to the injectors without pulling them totally out of the car - if you hear them click when you cycle them that's a good sign.
The tach is hard to say. If you have the original instrument cluster it's possible that the cluster is simply bad and needs to be reconditioned. Bad tachs are VERY common.
You are at the fuel/air/spark/compression stage of troubleshooting. If you have everything in some order the engine should at least try and fire up.
I would try pulling the throttle body elbow (the car will run perfectly without it) and have a friend crank the car over while you spray starting fluid into the throttle body. If it tries to start, semi-starts, or you hear combustion happening, that means you have spark and aren't getting fuel. If no combustion happens you have a spark issue. That can be from the crank angle sensors plugged in backwards, the trigger wheel missing or improperly installed, wiring to the coils, wiring to the ignitor.
FYI the car will start and run with no MAP sensor, it just won't run well.
I think in the shop manual there's some basic troubleshooting for testing that the ECU gets power and such. I would also double-check your fuses and make sure there aren't any blown fuses, even some circuits that don't seem related can cause problems.
The TPS also gets 5V from the ECU. If you suspect the 5V reference voltage isn't working correctly, try unplugging the TPS and using your multimeter (in volts mode, not current mode) to measure the voltage between the 5V pin and chassis ground. The red multimeter probe goes to the 5V pin on the TPS (make sure the red probe is connected to the Voltage/Resistance/Ohms plug and not the Current/Amps plug on the meter) and the black multimeter probe goes to an unpainted chassis ground or engine ground. If it's hard to work both probes at the same time and you don't have a second set of hands to help, try wedging the black probe onto the battery negative post/clamp, possibly using masking tape to keep it from wiggling loose. Even if you don't know which pin on the TPS is the 5V reference voltage, there are only four pins and it's easy to just measure all of them to see if one measures near 5.0 Volts. Depending what you find for the TPS sensor, try the same thing on the MAP sensor plug.
Even if they are new, that could also be the case - they've probably been sitting on a shelf for ages.
This was exactly what I was concerned about. The primaries are new OEM and went straight from the packaging into the rail without testing. I am kicking myself for not testing them against a 12v source before I put them in since I really really don't want to pull the rat's nest again. I have to take the UIM off to put the FPR in, so if the car hasn't started by then I'll probably test all of them. Hopefully I can wedge my fingers down through all the wires to pull the primary plugs without pulling the rat's nest, but iirc I didn't find a way last time. I'll test with starting fluid to see if I can get it to sputter.
Originally Posted by scotty305
If you suspect the 5V reference voltage isn't working correctly, try unplugging the TPS and using your multimeter (in volts mode, not current mode) to measure the voltage between the 5V pin and chassis ground.
I'm glad someone else suggested this since I also had the same idea but I wasn't sure if I was reading the diagram correctly. I did the same thing right before I posted in post #3 (though I guess I didn't post results). The harness lead that runs to the TPS is part of the new harness I put in and has a reading of 4.97v using the BR/W wire to the chassis ground I tested at the bolt for the MAP sensor. The MAP sensor lead still reads 0v on the BR/W wire.
I also tried to pull codes today, but my CEL does not flash any codes. I disconnected the battery to clear codes, jumped TEN to GND on the diagnostic box, cranked for 10sec, key off, key on. The CEL is on for about 2sec, off for about 3, then on continuously after that.
I gave the starting fluid suggestion a shot at lunch today. With a short burst of fluid, the engine will catch with a short (half second or so?) "brap", but will not stay started. A subsequent start attempt will catch for a very very short time on the first or second crank, but will not start further. I did a few cycles with a deflood in between and got the same results.
I also pulled codes after these attempts and the CEL did not flash. When I turn the key to "ON" with the diagnostic jumper in place, the light is solid for 2 sec, then out for 2 sec, then on continuously until I shut off the ignition.
The TPS and MAP sensors connect to the ECU via different harnesses. According to page Z-32 and Z-33 of the wiring diagram, connector X-05 (near the ECU) needs to be connected for the MAP sensor to get 5V reference power. If it's hard to access X-05, try measuring resistance between the BR/W wire on the TPS and the BR/W wire on the MAP sensor. There should be very low resistance (less than 2 ohms) between them. If you're sure X-05 is connected, but resistance isn't measuring as expected, look for damaged harness wires that run near the driver side fender. That bundle is known to get chafed and damaged by rubbing tires on lowered cars.
connector X-05 (near the ECU) needs to be connected for the MAP sensor to get 5V reference power.
YES, thank you for this suggestion! I checked between the TPS and MAP BR/W and found that there was no continuity, as you originally suggested. I inspected the X-05 and found that the connector was not seated fully, but once reconnected I was able to see continuity between the two BR/W points. I went and reseated a number of connectors in that area just to make sure. The car then started first try, though it's still pretty lumpy and smoking heavily from the tail pipe. All the coils are also firing, so this solved the trailing coil issue as well.
Off the bat, I am a bit concerned about the oil pressure being too high? I tested with the oil filter off prior to startup and saw that oil was flowing but I didn't get an actual reading from a manual gauge. My oil pressure gauge is pegged above 120 at idle and I'm curios if this is contributing to the smoke from the tailpipe or whether it is a bad reading from the gauge. I also was able to successfully pull codes after the engine ran for a few minutes and got the following: 05 Knock Sensor - open or short circuit (I knew this one was going the happen since I saw one disconnected)
16 EGR Function Sensor - open or short circuit (this is new to me)
23 Fuel Thermosensor - open or short circuit (I thought this might happen as the male end of the connector was a bit loose relative to the nut part)
On my car I see about 100psi (measured with an aftermarket sensor) on cold starts when coolant temp is around 5-10 degC and EngineSpeed is around 1500 RPM. I don't trust the factory oil pressure gauge/sender combination, they might have worked when new but mine are original and don't agree with my aftermarket sensor. The oil pressure readings on my stock dash are often too low, but there might be other failure modes that show readings too high. I don't think I've seen more than 105psi on my car, it looks like the oil pressure regulator is shooting for around 100psi. It's possible to rig something up using regulated compressed air or a MityVac tool to send specific pressure to the oil sensor to check if it measures correctly. The factory oil pressure sending unit is a 1-wire sensor that grounds through the engine, so you would need to rig up something to ground the sensor while it's removed from the engine.
That EGR code sounds familiar. Search or check the FAQ thread and you might find more info about troubleshooting, I think some people have described workarounds to trick the ECU into never throwing that code.
Fuel Thermosensor is a 2-pin connector on the secondary fuel rail, the UIM would need to be removed to check it.
EGR code sounds like you have a 94 ECU or California 93 where it's looking for the switch on the EGR that tells the ECU it moved when it was supposed to. Those switches commonly fail or it could be not hooked up/bad connector. It's a blue connector at the front passenger side of the engine.
Oil pressure can be high on a cold startup, I wouldn't sweat that too hard, I'd be more worried if you had little or no pressure.
EGR code sounds like you have a 94 ECU or California 93 where it's looking for the switch on the EGR that tells the ECU it moved when it was supposed to. Those switches commonly fail or it could be not hooked up/bad connector. It's a blue connector at the front passenger side of the engine.
Oil pressure can be high on a cold startup, I wouldn't sweat that too hard, I'd be more worried if you had little or no pressure.
Dale
The ECU is a 94 federal, N3C1. I double checked that the EGR is hooked up to the right connector, so it's very likely cooked like everything else. One small bright side to the emissions rules here for cars that are 1986-2009 is that an EGR code causing a CEL isn't immediate grounds for a fail as long as you can pass the dyno sniffer test. If my NOX passes with the EGR as is, I'll probably leave it for now until I get annoyed at having the light on. The other stipulation for passing the test is no visible smoke, which the car is currently failing miserably. I am thinking this is probably due at least in part to the injectors seeing 1.5x the normal rail pressure at idle, but I suppose we will see once the new FPR is here.
A lot of that smoke is probably just new engine smoke - a new engine will smoke pretty good until it warms up and burns off all the assembly lube. Also, all the parts on the engine that get hot will burn off oil from greasy hands, cleaners, etc. I wouldn't get too worried at this point.
For the EGR valve you can wire in a relay to fool the computer that it's working. The ECU tells a vacuum solenoid to activate the EGR. The EGR moves, the sensor on the EGR registers the movement, and reports back to the ECU that yes, it did move. There should be a writeup somewhere on using a relay to trick that system.
03-11-21, 02:18 PM
