gregaustex

Could use some help/advice.

Put tan top 1.8L injectors in my 1990 Miata thinking I might add a little more boost to my 10 years+ old Greddy based (+bov, intercooler, bell AFPR, MSD) 6 psi set up. Having issues.

Symptoms:

Rough Rich (as in soot out of the tailpipe rich and you can smell it) idle AND running.

Stuttering persists even in short ride around the block up to 4K rpm.

I don't mean a little hitch here and there, it is not really drivable (through technically you can drive it).

Some Info:

Bell AFPR
Walbro fuel pump in the trunk.
Seeing 40psi at idle. That's as low as it will get adjusting the AFPR.

The injectors were old and used, so I am wondering if this would be symptomatic of one or more bad injectors?

I have read that you can loosen the spring in the MAF but that this is usually only necessary to tweak things and that the stock ecu should allow the car to run fine without this tweak so I'd like to verify that's true.

Any help appreciated!

Thanks.

sixshooter

iTrader: (12)

Fuel pump is making too much pressure/flow for the fpr. Go back to a stock pump. A good stock pump will make plenty of power, much more than you should ever run with bandaids.

You probably won't take this advice because some buddy or some guy in a magazine has a Walbro that works and I'm just some guy on the internet, and how could a stock pump be better than anything aftermarket? It has to do with being the right tool for the job. It's akin to trying to use a 17mm socket to remove a 10mm fender bolt - you have more capacity than you need but it is to your detriment and not to your benefit.

gregaustex

Thanks!

In my defense it was fine for literally 12 years when I needed 40 psi (per Bell Engineering docs...OK 36 but they say up to 40) with my 1.6 injectors to avoid lean tip in. I have the Walbro 255 that everyone thought was the best option 10+ years ago and that is mentioned in this article http://miataturbo.wikidot.com/fuel-pump which looks like it was copied over from solomiata.

I had figured with the 15% bigger injectors this would be like running a base pressure at idle of 46psi which I had done for a while (50 actually I was a bit paranoid) with no issues. Where am I wrong in this thinking aside from the obvious (don't work)?

FWIW - popped the top on my afm and used a screwdriver to simulate a little more tension...no help. Actually started to falter either way very quickly. Supports the "overpowered fuel pump" suggestion I think.

I have a whole in tank assembly lying around here somewhere with a stock pump on it, I'll swap that out and see if it works for me.

I suppose this also means instead of the approximate right pressures being 36+8*psi, now I need to be looking at 31 psi idle and 7 psi/pound of boost?

So this probably isn't bad injectors? They were old. Not high mile, just long time in box in attic.

sixshooter

iTrader: (12)

The 255 has often overpowered FPRs in the past. I had a feeling that was what you had. The 190 was all a Miata ever needed from Walbro (but there are better options than Walbro anyway).

Good luck.

gregaustex

Switching to a stock fuel pump had no effect - though it did allow me to get my idle pressure down from 40 to the optimal 36. Decided to leave it in since I will eventually get the 1.8L injectors working and I think at that point even if I go 7psi I think max pressure required will be 80 or so which the stock pump may be able to handle.

At this point I'm calling it one or more bad injectors. Stuck my 1.6L injectors back in and she's purring again.

Time to google how to test injectors.

jmyr

iTrader: (1)

Sounds like bad injectors. Before you installed them did you try cleaning them? I had a S/C 94 a couple years ago that had the exact same symptoms that you are describing. I put in a set of new-to-me injectors that I cleaned and it fixed the problem immediately. Just something to try.
Also when I was removing the old injectors one was noticeably pretty beat up.
Just my 2 cents

gregaustex

Thanks Joe. Friend has a garage I'll see if they can do a thorough test. Worst case I'll buy 4 refurbs. Those plus the 190LPH and Narrow Band I have on the way should let me comfortably get to 9-10psi from what I can see which should be a heck of a boost from the 6psi I've been running all these years.

90civichhb

iTrader: (5)

Have you read about the EV14 injectors at all? Not sure what all is involved with using them, but for $25 a piece they seem like a logical replacement.