3TGTE fuel injector mystery

[pauljones1976]

Hi all. I don't usually bring my troubles to the forum, but maybe I should...

I've started allocating some time to unravelling the mysteries that are my RA23. The latest mystery I'm trying to solve is a weird fuel injection issue.

A little while ago I sprang a leak in my billet fuel rail. I had it fixed and when I put it all back together, I had a lot of air leaks between the injectors and the inlet manifold. I've been working through it slowly and I'm fairly certain I've solved them all now.

I am not entirely happy with the idle as it's not smooth - to be fair it's rarely ever been smooth since I've owned the car, but given I believe the cams to be stock I'd say it's some sort of vacuum related problem but god only knows where... I'd be very interested to know if things like the brake booster can leak and cause any problems. My setup is controlled by a Microtech MTX-8 so it's pretty simple.

But the problem that eludes me is reading the spark plugs. It seems that 2 of my cylinders plugs are very sooty although I always idle the car for 30sec or so after driving into the driveway (longer if it's been on boost) so I guess I can't really gauge much off this. The interesting thing though is that the other two are always cleaner. Here's a picture of the cleanest one:



I've moved the injectors around, and the clean plug(s) follow two injectors, or conversely the rich sooty fouled plugs follow the other two injectors.

It seems ridiculously obvious that this is an injector issue. But it's not seals, and last time I had them cleaned they are bang-on perfect when measured (I mean, the CC's are completely level from injector to injector). So I guess my question is:

What causes the difference in fuel delivery? Given that the injectors have been in different positions in the rail, and running off different signal leads, the only thing common is the actual injector itself. And given that they measured up perfectly on the machine, does this mean that at WOL they are accurate but when only being pulsed at idle or above they are unbalanced?

If anyone has any ideas I'd love to hear them. Oh and if anyone wants to comment on the condition of that plug feel free. It's not a nice looking thing, and they are relatively new. Oh, FYI they are BKR6EY-A plugs which I have been trialling (this thing makes 20psi of boost).

Thanks for your comments.

-Paul.

[Dan_k36]

Hmmmm sounds like injectors don't it, my first 3tgte had beening sitting for along time and once fired for first time it ran super rich, the injectors were just stuffed, couldn't be fixed, I'm pretty sure apart from cleaning the tips and putting a new gauze in that's all that can be done, so I just put vr4 galant injectors in and boom no more issues, saying that I did have air leakages from the rubber seals around the injector/ fuel rail area until I got some new rubbers and all fixed

[pauljones1976]

Dan, thanks for the input. I had a conversation with the injector cleaning guy that went along the lines of "oh, I think I'll probably just buy a new set of injectors and rule out those as the problem" but he laughed and said "they're mickey mouse I wouldn't touch them.." and since they are 550cc ones I'm wondering if it's really worth the cost. But if it fixes the problem I'll be more than happy to spend that money...

They were completely cleaned, and he replaced whatever could be replaced. I've had new rubber seals twice now - the first time I had lots of problems making them seal, but once they were warmed up and cooled down a few times they were ok - I've re-used those again to avoid the whole process. I'm really surprised how much trouble a new set of seals can cause...

Driving it around today it was great on throttle and running around it seems to have plenty of power. Spools up quickly and generally feels quite happy on the street. Idling for a while causes problems though and it's most annoying to have the plugs foul at a set of lights and spend the next minute or so clearing it..

So I'd love to know whether replacing the injectors is considered a good option at this point.

[Dan_k36]

I would just get some new ones, I went vr4 as they were same resistance and were 600cc, I paid 200 for the 4. But that was from the land of the import so won't be that here I'm thinking,
Are you still running the standard fuel psi regulator? They have a habit of splitting the rubber inside them

[pauljones1976]

Hmm the vr4 ones could be a good solution I guess.. I might start looking into this. I think it's running a SARD aftermarket fuel reg - rising rate. I don't think that's the culprit but I could be wrong, I might try replacing the vacuum hose on it as it looks a little ordinary. Although it doesn't explain the difference in the mixtures from cylinder to cylinder. And since it moves with the injectors that rules out head issues...

How did you source the vr4 ones Dan?

[Dan_k36]

I was lucky I was working for Mitsubishi so I got them cheap as, eBay should have them, or try trademe.co.nz they have a lot of that stuff and not to bad price wise.
Seeing your engine is early 80's I would suggest some new ones for price of mind, don't want it to lean out under boost and have a melt down

[Dan_k36]

Just reading your build says your running Mazda rx7 injectors? That correct?

[DX20VT]

We do injectors at work.

Injectors can get lazy in the springs inside them and cause flow problems, which only appear at low to mid opening levels,
at full flow the injectors will test perfect, the dont leak the dont dribble, they have the correct spray pattern,

but when opening and closing with small open times,
some can be lazy to close, so for a 3ms open time an injector with a lazy spring will flow more than a good one.

Usually this shows on an injector tester if they they do a pulsed flow test on a reasonably low flow rate.

[pauljones1976]

Dan, yes I believe they are RX7 injectors - well that's what I was told by the previous owner anyway. Could someone chime in on how to tell? Do I measure resistance across the terminals?

DX20VT thank you for your comment. That sure sounds like a plausible reason for my problems. I would be over the moon if a new set of injectors solved all these problems... It's certainly looking like I'll buy myself a set, once I figure out which ones I need.

I've been wondering also, could it be possible that I have a mis-match between the resistances of my injectors and that of the Microtech?

Cheers,
-Paul

[pauljones1976]

Update: I've had a look at the RX7 ones on eBay and they look the same as mine. I also have a spare injector my friend gave me which was faulty from his 300hp 12A and it looks the same as mine. So I'd be 99% sure they are definitely RX7. Question is now if I can match them up and put them in without a re-tune...

Just measured impedance is 13.6 ohms so that means they are High Impedance I guess?

[DX20VT]

Just measured impedance is 13.6 ohms so that means they are High Impedance I guess?

Yes which will rule out a mismatch of the injectors and ECU as no resistor will be required from them.

[pauljones1976]

Ok so does that mean i can use any high impedance injector as long as its at least 550cc?

[DX20VT]

if you dont use exactly the same ones it will need a retune.

if you are going to retune it you can use almost anything that will fit and flow enough.

[pauljones1976]

if you dont use exactly the same ones it will need a retune.

if you are going to retune it you can use almost anything that will fit and flow enough.

Thanks DX20VT. That's a great help. I suspect I'll be going down this road.

By the way, is there a big difference between a high end (expensive) injector and a low-end (cheap) injector for my setup at up to 250rwhp?

[DX20VT]

Apart from price, probably not IMO for what you will be looking at using.