Crispy Beef

I've been having what I think may be a fuel/electrical problem for a while now, upto this point it's been intermittent so I figured this would rule out a bad grounding somewhere. Now whatever the problem is, it's permanent as my FD will not start at all, the engine turns over just fine, so this kind of points to no fuel getting through. Here's the tests that I've done so far...

* Tested voltage at fuel pump relay terminal to make sure power is getting through (there is), but the relay itself doesn't click with the ignition on, so need to test the relay itself (I was told by somebody in a garage it was ok, but I'm going to double check myself tomorrow).

* Bridged the F/P and GND terminals in the data connector and turned the ignition on with the fuel filler cap off and heard the fuel pump come on. So I'm guessing the pump itself is ok.

Things to do tomorrow:

* Test the fuel pump resistor. From what I've read in the FSM and on this forum if this is knackered then the system won't operate in low voltage mode (9v I think) which is needed for starting up. If it is shot then I'll bridge it to see if that helps.

* Test the fuel pump relay myself and make sure it's not the problem as I have power at the box it plugs into.

* Test the fuel pump itself and make sure it's running ok and the correct voltages are getting through.

Anything else that I should check for? Before this problem came up I'd sometimes get multiple clicks from what I guess was the fp relay after turning the ignition on. It would click and then click on and off several times before settling down and working fine, has anybody heard of something like this before?

Just for information the car is a 94 FD, only mods are an EBC and a full decat. Couple of gauges too, turbo and a Billion VFC-Max which controls when the engine fans go on and off.

This is really getting me down at the moment as I've only just had the car back after having a new clutch fitted. Only got a days worth of fun out of it too...

Any pointers or help would be most appreciated.

mdpalmer

iTrader: (24)

Do you have a fuel pressre gauge? Measure the fuel pressure in the engine's fuel feed line while jumping the F/P and GND. Procedure and specs are on page F-97 of the 1993 (dunno if the '94 is different) FSM. You can get a cheap (about 30 USD total) mechanical gauge, tubing and clamps to do this test; see http://robrobinette.com/fuelp_gauge.htm

About the electrical stuff:

ARMAN

Hey Bro Hope u got it running, listen my car is staying in richmode and it runs with the fuel pump relay out of its box, any clue as to whats going on? where is the fuel resistor located?

Crispy Beef

Hey guys,

Haven't been back on the car since I've posted as I came down with tonsilitus. Will be back on the car this weekend with luck so will be able to do more investigations then.

@mdpalmer

I think I'll definitely get myself a gauge to check pressure as I have no way of telling right now. Have got to check a load of electrical stuff too so hopefull can get a move on all that thiss weekend.

Crispy Beef

Not running yet no...

From what I've read up on - and I'm no expert - it sound like your fuel pump resistor has been bridged. Normally that resistor keeps ~9v going to the pump and then the fuel pump relay (speed) will up that voltage to ~12v for maximum fuel delivery. Some people bridge the resistor which results in the engine running a bit rich as lower speeds and idle (could be a problem for emissions test?). I think this is more useful for single turbos and not sure if it's needed on a standard twin setup. Somebody please correct me if I'm wrong here.

If the resistor is not bridged then I wouldn't be able to say what's wrong to be honest am just getting into this stuff. Am sure somebody else reading this might be able to suggest possibilities?

The resistor is located underneath the brake master cylinder which is a big black cylindrical things attached to the drivers side firewall, in theory you'rs will be on the other side to mine as I have a RHD car from Japan (UK based).

DaleClark

iTrader: (55)

If the fuel pump gets power, that's not the problem. Even if it runs in 9v, 12v, 14v, whatever, it will get enough fuel to start the motor.

I think your problem lies elsewhere - maybe your motor is simply flooded?

If you can hear the fuel pump running, and nothing major has happened to the fuel system since it last ran, I would look elsewhere. The fuel pump's control system is pretty hardy and is not a common failure point.

Dale

ARMAN

The motor has had a fresh rebuild with 3mm seals all new seals everything, But my problem is in the fuel system, I know this because the fault codes from mazda said there is a short circut or a ground problem somehwere in the relay system,and besides should my car be running with the actual fuel pump relay out of its socket, i also have a RHD vehicle in from aus.I have bought a new engine wiring harness a new ecu maping sensor played with the tps all that crap taken it to 7 auto-elec's no one knows whats wrong with it i think its just one stupid wire somewhere, Theres been no excitement in it for me as this is my first rx and i spend $400 a wekk on petrol...!! And risk screwing my engine. Thanks anyway
for the help guys

Crispy Beef

The fuel pump only ran due to the data connector F/P and GND terminals being bridge in the data link connector. Without that bridge it doesn't run. The car might well be flooded, but until I here the relay click and the pump turn on as it should there's not much I can do about it?

Crispy Beef

That's one thing I haven't checked for yet; fault codes. To be honest I'm not entirely sure how to either. Have looked through the FSM for details and done a search on these forums but not too much info. Does one of the main RX-7 sites have details on this?

All that will happen with the pump running at speed (~12v) is that you'll run rich in lower revs/speed, if it were running lean then I'd be a lot more concerned.

What is odd is that the fuel pump works from the start as the main relay for this needs to be there to complete the circuit. Even if that relay is bridged somehow then the resistor should drop the voltage to 9v anyway, so it's sounding like this whole system has been bypassed somehow.

Maybe the other fuel pump relay (the speed one) has had something done to it, or the wiring to it's block? It is location under the airbox to the front left of the engine bay as you look at it. Worth checking there too.

If you look at page F-108 in the workshop manual (you can download it from here) you can see how the circuit is supposed to work.

Efini_7

iTrader: (1)

That really, really sounds like a grounding problem to me. I've had all different kinds of symptoms and ~95% of them were because of a loose ground somewhere. If you've gone through a bunch of stuff and can't think of anything else to check, take off your uim and make sure EVERY wire is securely connected and clear of corrosion or dirt.

Sorry i can't be more specific, but i hope this helps.

ARMAN

Thanks boys, do you guys know of a wiring diagram for the fuel system all the grounds and everything can u post me the link, i might as well check it from start to finish as i have the day off today, appriciate it. thanx

ARMAN

Crispy beef let me know how your car goes and if u can be bothered try starting your car with no fuel pump relay see if it starts or try pulling it out of its socket while the car is running see if it turns off lol.

Crispy Beef

My next step will probably be to bridge the relays with some wire and see if the thing fires, at least I can rule out the circuit being dodgy.

By the way, if I bridge the terminals F/P and GND on the datalink connector the get the fuel pump going is there anything wrong with trying to start it then? Would something bad happen or would the pump just run at a fixed voltage?

Crispy Beef

Sorry, losing track a little, is that in response to my original post?

ARMAN

ok as far as i understand and what my mechanic has told me, The fuel pump starts off in 12.2V mode after a little while it should switch out of 12.2V and into 6V for low rpm range,
From lookin at the wiring diagrams the Fuel (speed) Relay should take care of this and the ecu will give the command for it to do so,"Switching the relay on and delivering the 6V to the fuel pump" and the resistor will provide the resistance to supply the relay which will supply the fuel pump with 6V. so after your car has warmed up if you test the voltage at your fuel pump on idle it should be around 6V is this the case with your car?

Crispy Beef

Problem on my car is that it won't fire at all (no click from relay = no power I guess), the only time I can get the fuel pump to operate is if I bridge the terminals in the data connector. I'm going to go out now and have a nose around and see what I can find.

ARMAN

have you tried the fuse box in the interior i blew a few fuses in there and there is 2 main fuses

ARMAN

that break the circut an engine fuse and a fuel pump relay fuse, which is wired up into the resistor and speed relay one of these must be engages for the fuel pump main relay to work but the fuse is for the relay as the resistor is also feeding off the speed relay. Try the interior.

Crispy Beef

The interior fuses were one of the first things I checked and were ok, I'll double check them later to make sure I got the right one and didn't miss anything. Got some decent time on the car today and determined to rule out things.

Crispy Beef

Hmmmm, still no go here. Today have checked out all the relays and they are just fine, applied voltage to them and they all clicked nicely, also tested the resistance and that seemed ok too (~.4 ohms).

Double and Triple checked the 15A engine an 20A fuel pump fuses and they're both fine.

Here's something else that I didn't notice before however; when turning the ignition to IG2, in addition to the fuel pump relay clicking on, the exhaust overheat warning light used to come on for a bit and then go out, this light does not come on now. Another thing is one of my gauges - Billion VFC Max - always had power to it too, but not any longer...all other dash lights come on as expected and the engine still turns over.

The way I figure it is if I can work out how the gauge and the exhaust warning light connect into the system I might be able to figure out what's going wrong and where.

I've also checked for any error codes and none seem to be coming up. Just to make sure I've done it correctly this is how I did it...

Bridged pin TEN to GND on the data link and then put the ignition to ACC (accessories), from what I understand the engine warning light will then blink the codes out in a series of long (10 second) and short (1 second) flashes. That sound right?

Crispy Beef

Starting to lose the will to live...I've tested a load of the grounds today, also had the battery out and quick charged it to make sure that's ok. All grounds tested checked out and the battery is fine.

Have been doing some more searching on the forums and come up ith some options, could the problem be to do with a dodgy starter cut relay or starter interlock switch? What would the symptoms of one of those two being knackered be?

I don't think it would be the interlock switch as I've just had the clutch replaced and this problem was there - in intermittent form - beforehand.

mdpalmer

iTrader: (24)

Whatever you do, don't kill yourself. : Just kidding

A couple of other simple things (don't remember you checking them):

1. You sure you're getting good spark?
2. Does your engine have good compression?

I'm not much of an expert, but I have a motor with bad compression. When I try firing it up after it's warm (I know this doesn't really pertain to you), it will crank and crank and crank, but won't start.

Good luck, hope you figure out your problem.

ARMAN

Check the wires that run under the front guard, somebody told me yesterday they can rip from the wheel hitting them.. see if they are ok in that area.

Crispy Beef

What do you mean by front guard, do you mean under the wheel arch or somewhere else?

Crispy Beef

Have managed to get some sleep so things don't seem quite as bad this morning...still won't start though.

I'll check the plugs etc. later and see if they're all ok, they haven't long been changed and everything in that department always seemed fine, will double check.

On testing the compression I'll do a bit of a search as I'm not entirley sure how to do it properly.

I think the main issue is getting the fuel pump to prime, then I reckon it'll be plain sailing all the way.