Why Do My Fuel Injectors Keep Failing? And Solutions?

The XR4Ti rally car (Ford 2.3T) eats fuel injectors like it thinks they're snacks- I have 12 stock injectors as well as a set of 4 Tomcos, and cannot seem to keep an installed set happy for more than a few hours of runtime.  One of my nearly-new Tomcos just failed, which I bought because they were well reviewed on the Merkur forum and cheap, but I'm willing to entertain the idea that those are just low quality.

First question: why do we think they keep failing?
-Just old/cheap/crappy
-Something wrong with the fuel system (has an in-tank filter as well as a 40 micron filter before the fuel rail)
-Something wrong with the electrical system (stock Thunderbird stuff)
-It's just a really harsh environment under the hood of a rally car and this is expected

Second question: what do I do about it?
-Buy a set of Injector Dynamics injectors ($$$)
-Send out some of my stock ones for cleaning/rebuilding (who is good for this?)
-Keep feeding it injectors (annoying, unreliable)
-Some other fix because something else is causing this

Thanks!

Do you know what's actually failing? Do they get clogged up, burn out, set the car on fire?

Few things come to mind. 

System voltage, check at all rpm

Fuel pressure in tolerance? 

Fuel line and tank free of debries

Excessive alcohol in fuel? 

What is injector duty cycle at high rpm?

In reply to BoxheadTim :

They stop injecting, generally.  I did have a set from Standard Motor Products which set the car on fire, they got returned with a nasty email.

In reply to TGMF :

Voltage 12.5-14.5v throughout rev range

Fuel pressure is correct for the application

Fuel system as free of crap as it can be, the tank filter gets dirty eventually but typically there isn't any junk that makes it into the fuel rail as far as I can tell.

Fuel is (usually) Sunoco 93 octane, standard ethanol blend

Duty cycle is whatever stock is for a Thunderbird Turbo Coupe, I think.  The engine does have some "breathing mods" but only running 15psi boost maximum at this point, which is the stock pressure.

Its a ford. They circled the problem for you.

Have you checked the temps of the injectors during hard runs? Wnder if it's heat related.

Check your failed injectors with an ohmeter. If they have gone to infinite resistance it is likely over voltage, or heat problem. If they still read the same as known good injectors keep looking at the fuel. 

What Turner said, but with an additional question - who is the OEM, and are you buying OEM replacement or cheap reboxed aftermarker?

IIRC, 2.3 Turbo motors used low impedance injectors. These need some form of current limiting to avoid overheating, and it appears to be built into the ECU. I'm not sure if Ford put power resistors in series with the injector outputs, or used a true peak and hold driver, but if somehow the current limiting has broken down and allowed full current, that won't be good for the injectors.

no advice here, but it makes you feel any better, you're not the only one chasing fuel/electrical issues that seem to be unsolvable. 

Resistance of the two failed injectors I checked matches good ones- so we think fuel or garbage in the fuel?  Totally possible, maybe I'll take one apart.

I pulled the filter screen out of the most recent failed injector, looks clean.  Hmm.

These old injectors are not designed for ethanol.  Stop using corn syrup.

Just drove it, had another injector fail.  I don't buy that it's ethanol killing them, I have had plenty of other 80s cars and this hasn't been a problem on any of them.

Have you tried taking a “bad” injector & triggering it on the bench with fuel(or other liquid) fed to it & watch to see if it sprays?

In reply to Pete Gossett :

The bad OEM injectors won't do anything.  Bad Tomcos will spray until they heat up, then stop.

Another data point- the vast majority of the failures have been #1 and #4.  Maybe that points to the ECU/current issue?

Injector driver inside the ECU then.  Ethanol does ruin injectors too, but it doesn’t burn them up like yours seem to be doing.

Yeah I’m thinking either new ecu or megasquirt time. 

As a test, you might be able to put a low-value resistor in series with #1 & 4 injectors and see what happens. I have no idea what values may work, but if you go too large they won’t work at all vs too small where they won’t offer any protection. 

Ebay had a replacement ECU, so I bought it.  This isn't the first time I've suspected an ECU problem so even if it's not the culprit it won't hurt to have a spare.

What's the current draw on 1&4 v. 2&3?  Put an ammeter in series.  But, yeah, either the ECU or a current limiting resistor problem.  Is there a current limiting resistor in there?  Early Toyota injection had those.  Ford, I dunno.

¯\_(ツ)_/¯ said:

Ebay had a replacement ECU, so I bought it.  This isn't the first time I've suspected an ECU problem so even if it's not the culprit it won't hurt to have a spare.

I'm amazed you have an '80s racecar, and no spare ECU. I think I had like four spares for the BMW at one point, haha....and two for the Porsche. A lot of the german 80s ECUs are known to break solder contacts and cause issues.......

In reply to irish44j :

The "good" 2.3T ECUs are surprisingly hard to come by.  I have a spare one but it's the not higher power Thunderbird version I currently use, so I'd need to swap the spare engine harness in with it.

The fuel injection resistor business all happens inside the ECU as far as I can tell.

I had checked grounds before, but today I gave the main ground wire for the engine a good yank: 

What do we think the likelihood is that this was the real problem?  I think it was only really held together by heat shrink.