tomatoto

Hey,

"My 92 fd cranks but won't start..." and I've no idea why.
When cranking, there's definitely no explosion at all (see video below)
This problem appeared for the first time 2 months ago after a 1 hour trip, I stopped the engine for 20 minutes and when I wanted to start the car again, it cranked but wouldn't start. No explosion, like if there wasn't gas, or firing. I insisted cranking and after like 20 tries, it did start and I drove back home normally. The next days/weeks, it started normally and drive flawlessly. The problem only happened a few times since then but I only had to keep cranking some times and it started until 2 days ago, after the car sat for 1 month, impossible to start even if I keep cranking several times...

Here are the things I've done / checked so far:
-new battery (yuasa 12v, 60ah, 550A) fully charged, I also tried connected to a 610A battery.
-Spark plugs were 4 months old, but I replaced them anyway with brand new.
-when I crank, I can smell a distinct gas odor in the catback, so I assume the injectors are working. I also can hear the fuel pump working and check its voltage, I changed it along with secondaryisecondary and replaced FPR 4 months ago)
-I checked the igniter grounding and harness. Looks all fine to me.
-I checked the 3 ignition coils 4 months ago (they were OK) and cleaned the grounding point. The spark plug wires are
-I rebuild the cable at the battery terminal (it was not great) and added 2 brand new 2awg grounding (battery to shock tower, and shock tower to engine)
-I tried with stock ECU : same problem
-I checked one spark plug out, connected to the wire and put against the housing : I made several tries and there is NO FIRING at all... except the first attempt this morning after I kept charging the battery all night long : there was a distinct lighting coming from the spark plug and the engine almost started on the other rotor. It worked like 3 seconds but I stopped cranking, and since then it's not working again, NO FIRING at all.... I'll try tomorrow morning again, who knows?

any ideas ?

for info, the car is mostly stock, oem coils, oem injectors and rail/fpr... The engine has been rebuilt 2years/2k miles ago, the compressions are good (+108psi), I'm on PFC ecu and I can't find any lead from the sensor check with the commander.
you can see and hear it cranking on this video :
I have few other problem that MAY be related, i don't know ?
-The Ignition Lock has always been weird : I had to make special moves with the key in order to turn it on, and even when the engine is running I can remove the key and the engine keeps running...doesn't seem normal to me. Can it explain that the spark plugs are not firing ? I've no idea...
-My PFC ecu is not perfect : the transistor that enable/disable the fuel speed relay is defective and let the fuel relay always off, so I've only get small voltage at the pump. I jumped the speed relay in order to get full 12V at the pump now, but maybe there's another defective component in the ECU that can explain why the spark plug don't fire ?

JuSanBee

iTrader: (3)

This one kinda stumps me, Maybe your coils are on their way out. IGN1-A time????!!!
Did your old plugs seem pitch black and smell of fuel? A bigger battery might help too, keep it spinning harder/longer.
You know if your compression is good? I know some cars have problems starting when that starts to go below 90 PSI.

Also make sure your grounding is metal on metal and not being insulated by paint.

tomatoto

I doubt my coils are going bad all the 3 at the same time... is it possible ?
I did an attemp with another battery (630A) but thas wasn't better.
Yep, my compressions have been check just a couple months ago and are good (above 105psi) (I updated the foirst post ith the info)
For my grounding, it did them the right way following Aaron cake's page, cleaned metal and dielectric grease..
The plugs were really black for 4 months old plugs indeed. And they smelled a little gas indeed, but I guess it's normal since the engine was kind of flooded at the time.

JuSanBee

iTrader: (3)

Hmm strange, That would make me nervous about the PFC sending fuel or not. I remember when I once forgot to plug my fuel pump back in It definitely attempted to start and kept making this funny noise I can only describe as farting and popping. Until I ran out of gas in the lines then it sounded like yours did just spinning with nothing really happening. Could try shorting the pump on the diagnostic port to make it run I know there is a page around here somewhere on how to do it and see if you can hear your fuel pump. Maybe check the connector and see if it gets power when you turn the key initially with a multi-meter. I'd be suspect of that fuel pump tbh if you got your old one swap it back and see what happens.

Your plug looks brand new probably just a little gentle steel wire brushing should clean it off and it will be good as new. I expected them to be waaay blacker actually they usually reek of fuel if they flood. I do know these cars can run with just the trailing plugs igniting. It's not as happy doing it but it'll do it. Same with just leading firing.

As long as the grease isn't between the connector and the metal it should be good! It doesn't conduct electricity btw so if your plugs can't fire that could be a thing I always take it easy with that stuff I had a friend go buck wild and fill a spark lead jammed up with the stuff thinking it waterproofs everything and then he couldn't start his jeep

7sins

This is your best friend when checking for spark.

https://www.harborfreight.com/90-in-...AaApytEALw_wcB

try to find something like that in your area. as far as your starting issue it is one of 3 problems, compression, fuel at the right time, and spark at the right time. sounds like you ruled out compression but if the car sat a seal could have stuck... but not likely. sounds like you are getting some fuel into the engine although we are not sure if it is the right amount, may be worth checking fuel pressure to see that there is enough pressure to provide adequate fuel to start. lastly try to find that tool and check for spark with the plugs installed, and check at least both leading plugs. should get a strong flash from the bulb in that tool if one or both are weak or not flashing ignition is the problem. check those out and let us know what you find.

tomatoto

Thanks guys!
since i can hear no explosion from the engine and can smell gas in the exhaust, I believe the problem is coming from the ignition.
I didn't know this spark plug tool. Looks very handy, i just ordered 4 of them so I can check them all together soon !

DaleClark

iTrader: (55)

Just by hearing your engines crank I can tell compression sounds good as well, I doubt that's it.

The original coil pack harness had a ground wire, if you have that wire you have the old harness. The updated harness doesn't have a ground wire. The old one can have problems but usually it's a high RPM breakup or something, it's not going to keep the car from starting. But that may be worth replacing at some point.

Did you test the coils with a multimeter? The test in the shop manual is pretty dead on, if it passes that test the coil is good. If you had a bad leading coil that could prevent a start.

What kind of shape are your plug wires in?

Dale

tomatoto

Indeed, it looks like I have the original harness, as I can see this black wire ground here :




I'm quite sure I cleaned it (sanded) and connected it firmly when I mounted back the coils 3 months ago. I tested the 3 of them with a multimeter and they were totally OK according to the FSM.
I totally ignored there was a new harness, and that the old one could fail. So I'll change it asap and see !
My plug wires are the OEM ones (mazda from Atkins) in blue and black fashion I replaced them less than 2 years ago and they still look like new.

For the compressions, I can confirm they are great, because...
the car started today !
after cranking it like 30 times in the morning with no success, I let it sat for 2 hours and I came back in the garage, I didn't touch ANYTHING on the car, just pushed the key in and turned it, it cranked and the engine started INSTANTLY (like in 0,2 sec). I drove it for 40 minutes like a charm, even in the high rpm/boost...
I get back to the garage and stop the engine. 30 minutes later, I start it again and notice an anormal voltage at the fuel pump (4V when I usually get 7/8V), it start but stall immediately. I start it again, stuggle a lot to keep the engine "alive", and a few seconds after the voltage raise to 7/8V and the engine idles fine... wow, I never experienced this before and can't understand what happened here.
I let it sit 30 minutes again and try again : again, 4V at the pump but just 5 or 10sec later I get 7/8V and fine idling. I stopped it and restart it and it starts normally.
So I left it sit for the night, but I really don't know what to expect tomorrow morning...

7sins

4v at the fuel pump is nowhere near enough voltage to run the pump. 7 or 8 might be right with the resistor, i would have to do some math to be sure. depending on how comfortable you are with electrical diagnosis you can try to voltage drop the circuit to find the excessive resistance or for a cheap diagnosis you can try bypassing the resistor (assuming you have not done a fuel pump rewire) by jumping the fuel pump relay pgZ-28 in the FSM. bypassing the resistor should give battery voltage to the pump when the circuit opening relay comes on. if that is the case it would be a good idea to permanently bypass the resistor and do a fuel pump rewire.

DaleClark

iTrader: (55)

I think at this point you need to figure out what's going on with the fuel pump circuit, I think that may be the cause of problems. If that output from the PFC is bad I would look into repairing it or replacing the PFC. Or, it may be worth bypassing the 9v/12v and run the fuel pump at full 12v to see how that does.

Plug wires should be fine, those are the way to go there. Coil pack harness may be worth doing at some point but I wouldn't get super excited that it will do anything magical.

Dale

JuSanBee

iTrader: (3)

It should be 9v on low mode (6-8 in actuality). I think it shouldn't be on low mode when starting though due to the MASSIVE voltage drop/amp suck from the starter. It might keep it on high mode when starting to compensate for that then drop once idling which could obviously point back to your PFC issue. I'd definitely look into that actually. You could just rewire it into full power all the time mode. I'm sure someone here has done it before.
Check this out https://www.rx7club.com/3rd-generati...l-pump-847009/

7sins

if the PFC driver is bad the fuel pump would get 0v instead of the reported 4v as the relay would never come on. it sounds like excessive resistance in the fuel pump circuit, most likely on the low speed side. if it were my car I would jump the fuel pump relay (high speed relay) and see if that clears the problem up, cheap and easy to do. depending on the results of that I would make a more permanent repair.

tomatoto

I tried the speed relay jump 1 month ago when I found out my PFC keeps this relay disabled. While jumped, the car would idle fine and drive fine unless I boost or go beyong 4500rpm, at that point it behaves like crap, missings, catback explosions, boost stuck at 5psi... really weird, but maybe this is happening because my mapper did the mapping with my fuel pump stuck on 8V ? Maybe I should restore default settings/mapping on the commander then, until I go for a new mapping.
Anyway, I'll try again with the speed relay jumped and see how it's going.
Actually, the last few days I already tried to start the car with the speed relay jumped, but it didn't help in my starting problem. I really don't know if those 2 problems are linked actually. (FP low voltage and cranking without starting), this real low 4V voltage I had today, it was the very first time I notice it.
I'll try it tomorrow and let you know.

btw, I did the fuel pump rewire (Dale Clark way) recently, and I noticed a couple more volts at the pump... when I jump the fp speed relay I get a strong 12V

tomatoto

I forgot to mention, when I wanted to start her after my 40min ride, there was a buzzer I never heard before. Not exactly the same as usual, that one seems quicker than the usual one and it didn't stop
Luckyly I was filming, so you can hear how it was hard to keep the engine alive, and see the low voltage

https://www.youtube.com/watch?v=rwjsQpmvsU4

in the second video it was 30 min later, the voltage raising from 4 to 7V...

https://www.youtube.com/watch?v=-J131AOfYe4

7sins

i am surprised it is running with that low of voltage at the pump. is the meter ranged correctly (20vdc)? your AFR is a little lean but not outrageous. if you aren't getting battery voltage at the pump with the rewire then something is wrong. I assume you ran a new wire with a fuse from the battery to a relay then to the pump? either way you need to get 12v to the pump before continuing on. from there I would want to know what your fuel pressure looks like. low pump voltage will cause fuel pressure drops and lean conditions. jumping the fuel pump relay is just a test to see if the car will start when there is 12v instead of 4v to the pump, I would not go driving around like that. do you have a datalogit?

tomatoto

I'm also pretty astonished by this so low voltage at the pump. (4V)
My voltmeter is automatic but reliable. Maybe it's my setup that is not correct. In order to check FP voltage while driving, I extended the FP connector's wires in order to put the voltmeter clamps on it. I know it's kinf od shaky install, but I'm monitoring correct values since I'm using it. If there's a better way to do it, please let me know.


**:don't mind the rose/orange wires, they're the power wire for my Water Injection motor (disabled at the moment)


Well not really, I did the simple rewire, which consist of giving a better source (a spare one in the EGI relay box) to the original wires to the pump.
I have a solid 12V when the speed relay is switched/jumped when I drive, and tomorrow I'll check what voltage I get when cranking/starting the car with the speed relay jumped.
Fuel pressure wise, I don't know exactly, but I'm using a (new) oem FPR (and a oem old fuel damper)
Unfortunately, I don't have a datalogit.

JuSanBee

iTrader: (3)

Put your seatbelt on! jk lol It's just the "hey you need a seatbelt and close the door" buzzer. FD is just saying helloo
Fuel pump consistency definitely could be the issue actually. If your pump flow isn't matching what it was tuned on it could throw the entire fuel map off. Your pressures/flows won't be consistent anymore and the PFC is referencing whatever you had it at before.
That would totally explain the fuel smell and not starting! It's got fuel but just not enough to really get going. I imagine once you get the fuel pump power back to normal you could adjust the idle fueling and get it to stop being so stubborn and not turning on.

7sins

something like that will let you probe the connector while it is connected to the car. those came off of a tool truck but you can get something similar from walmart or any place that sells sewing supplies, they are T pins. If you are getting battery voltage with the fuel pump relay jumped I would suggest doing the full fuel pump rewire. get some decent gauge wire 10-8 should suffice, a 30a relay, and a fuse holder with a 30a fuse. run the new wire from B+ to the pump and use the old wire to power the relay coil and ground the other side of the coil. alternatively I think SBG sells a kit that makes it easier to do. if you need help or some pics of an install I can try to walk you through it. once you have battery voltage to the pump consistently we can continue diagnosing if that does not fix the problem. hopefully auto parts store in your area will rent you a fuel pressure tester.

*edit* you will probably also need to bypass the fuel pump resistor as I am guessing that is what is causing the extra resistance.

tomatoto

Thanks ! I've ordered those pins, looks very handy, so I'll check voltage and be reassured my FP is well connected with the connector. I'm waiting for the spark plug test cables too, eventhough I'm not experiencing any starting problem since it started back 3 days ago.
Yesterday, it started flawlessly again at the first try (see video below)
I had the fuel pump speed relay jumped and I got constant 12V while cranking and starting and during all my 30min trip, as you can see :
Afr seems ok, though I just can't boost at all because the mapping was done on 7V and is now totally out with the constant 12V.
When I stopped it, and restarted it right after, I didn't experienced the low 4V voltage, everything was fine...
I may do the full FP rewire anyway, but I'm not sure if it's the cause of my problems and I would really prefer avoid it because I'd like to keep it as stock as possible.
I know I didn't fix anything of the problem yet, but this is very tricky to troubleshoot it when the problem doesn't occur at all.

7sins

glad you are making progress. chances are the problem will surface again and those tools will help you find it. as far as your boosting problem is concerned it could be that your mapping is off from a low fuel pressure problem when the car was tuned. other than that the FPR should keep fuel pressure nominal provided the pump can supply the fuel.

"I know I didn't fix anything of the problem yet, but this is very tricky to troubleshoot it when the problem doesn't occur at all."

yup this is what I had to deal with constantly, try convincing your service director of this . intermittent problems are a nightmare and always seem to surface when the car isn't in the shop/ no tools around. as far as the stock bit is concerned you could wait and try to find the excessive resistance when the problem occurs again if you feel comfortable with electrical diagnosis. if you want to keep the factory FPR I highly suggest getting a fuel pressure testing kit, it will be invaluable in diagnosing problems like this.

once you have the fuel pressure problem buttoned up and the car is starting and idling normally then you can start addressing the tuning issues or take it to a tuner to get it sorted. gl and let us know what you find.

tomatoto

That's exactly what I'm looking for currently ^^
Then, I'll be ready for the next time that s*** happens :!

I don't need an high end gold plated gauge, just something casual and handy to install when I need it only, do you have a specific model to advise me?
I've seen that kind of cheap kits, but... any chance they are reliable ?

DaleClark

iTrader: (55)

For testing fuel pressure you want something that you can tee into the fuel feed line. Many testers are designed to screw in to a special test valve on the fuel rail, many modern cars have this. The FD doesn't.

I have a small gauge screwed into a tee that I've used in the past. The only downside is it's only good for testing fuel pressure with the car stationary and the hood up. Doesn't help if you are driving around.

This is what I have -



Something like that can be temporarily installed and left in place for a spot check.

Dale

tomatoto

Thanks a lot, Dale !
I've received a fuel pressure kit with that tee, but I've no use for it yet since the car is still working perfectly... as you can see : I connected back the fuel pump harness's connector, and now taking the voltage with a T-pin, works great ! It gives me even better voltage : 12,5V during startup, and when driving/idling at a steady 12,3 / 12,4V.
So I keep my finger crossed for the moment, and let you know here when it occurs again.

7sins

I bought a cheapo harbor freight kit and it works great, i wouldn't expect to survive shop abuse but for as much as i use it the gauge set will probably last until i'm gone. I wonder what changed to give reliable voltage all of a sudden... at any rate keep an eye on it as it will likely happen again.

tomatoto

Just a little update here,
I had my garage totally renewed, so I didn't use the car much these last months, I just drove it every 2 weeks for small trips ( 20 minutes. )
And it fired everytime, instantly... Even when I let it sat for +3 weeks... So, I still don"t have any clue what the problem is (was)
Since I've jumped the speed relay, the Fuel Pump always has its 12V, from start to cut off, steady.

I removed the PFC ECU today, and I'll resolder a brand new chip that I ordered a few weeks ago (not easy to find it). The one meant to manage the fuel pump resistor (speed relay). I'll see if it works or not... otherwise, I'll totally get rid of the FP resistor and keep the speed relay jumped.