Missatched injectors
 

Hey guys so I have an 87 fc NA with 3800 hesitation which I'm currently troubleshooting. I just finished re-grounding her with no change. The car is fairly new to me so I'm still going over all the records and paper work from the previous original owner. I just realized there's miss matched injectors.

looks like Tri Point Engeneering did the work on the car (great shop, I use to go to them in the past with my previous rotarys), they changed out the secondary injectors "temporarily while they found the OEM one's. I can only assume they are larger aftermarket injectors? I'll find out.

could this be a potential culprit to 3800 hesitation? I haven't seen this covered in any of the dozens of hesitation threads i have read. And aside from the hesitation, is this something that's WRONG and should be fixed immediately?

so to clarify, I believe the primary injectors are OEM and secondary are a different brand and potentially larger size.

car runs great aside from the hesitation so if this isn't a big deal to have mismatched injectors, I'll leave it be.

thanks!

if they were bigger then the hesitation would be less noticable, if the impedence is wrong then that can cause issues.

without any real information, no one can answer your questions without having some information on the injectors.

Do you have a multimeter ? Being that its the secondaries youre dealing with, its real easy to check the impedance. Go to harbor freight if you dont own one and spend 6 bucks on a cheap digital multimeter. Set it to ohms and remove the clip off the injector to gain access to the pins on the injector itself and meter them.

Having the wrong secondaries will absolutely cause a strange and somewhat violent hesitation when those come online.

Additionally, all 2nd gen ecus need to see a high impedance signal. Earlier cars have a resistor pack under the airbox to take the low signal to where it needs to be. Later FCs have no injector pack, but instead use high impedance injectors.

Using the wrong injector set will eventually (sometimes very quickly) burn out the injector drivers in the ecu - at which point your pooch is screwed and a kitten somewhere has expired.

If it were my car, I'd meter those injectors asap and figure out what is happening here.

If you need NA injectors, pm me. I've got bags and bags of them lol

So I checked out the order form from Tri Point Engeneering and found the injectors they installed. I also went out to the car to verify the part number and can confirm they are: SL9-0440

I found the part online: https://www.rceng.com/Saturated-Inje...440-P37C6.aspx

which reads Resistance: 12.5 Ohms @ 68 F

If I'm not mistaken, these are high impedance?

With that said, I believe my stock injectors on my model are 460cc. Would these being 440cc be a big deal?

Thanks again, guys.

being your car is an 87 it should have low impedence injectors, but to be sure you should see if there is a metal rectangular box under the intake box, which would be the injector resistors.

if you have high impedence injectors and also the resistor box then the ECU is going to be seeing something akin to 24ohm, which will cause a huge delay in the injector operation, and your hesitation.

Interesting, I thought I needed to have high impedance. What year did the low to high impedance change? 87.5? Can I tell with my vin number? I'll go out to check for the resistor when I have a moment.

If this is wrong, it will be very surprising to me that a reputable rotary shop would have done such a thing. That is again for the info and I'll get back once I've checked my car.

Yes, I see the resistor!
http://imgur.com/RtGCSug

So I assume the right thing to do is get the proper injectors? Or is there a way to bypass the resistor or something?

Should be your problem.

You could cut some wires and bypass the resistors for the secondaries in the short term, but then you have hacked your harness up... is this your only car ?

does the resistor work for both primary and secondary or are they separated to where I can just have to bypass the secondary alone?

I'd love to test it out but I would hate to mess with the OEM harness. This is not my only car. Just a weekend car.

Been looking at reversible ways to test this out and came across this:
Injector Resistor Bypass

thoughts?

also, could someone please clarify if doing something like this will now interfere with my low impadancy primaries. Should I just get my hands on OEM secondaries and call it a day?

Yes of course you could bypass just the secondary resistors. But given its not your daily, just park it until you get the right injectors.

THANKS! now to PM you about getting some from you.

i agree, it's always best to just do the repair the correct way and those injectors are wrong, install the correct injectors and save future headaches down the road even if you did get it working 'okay' with them.

generally it is only the 1988 model year cars that do not have the resistor pack and have the old style injectors with high impedence, however the notch for the injector plug is offset instead of in the center like the low impedence 86-87 injectors. ie 87.5-88 year cars are generally designated as 1988, i have never seen any exceptions in that.

Quick update
 

So I bought the proper fuel injectors from Acesanugal (awesome person!), they were ohms tested and looked good, I dropped new o rings and grommets that I had on the previous injectors which were new (but slightly different gromet design), dropped them in and... hesitation is gone! Haha well, not really. Now it hits that 4k wall and doesn't drive higher than that unless I ease off the gas to where it doesn't require the secondaries.

acesangual says he's had similar problems in the past where the secondaries where clogged so he's being extra nice and sending me another pair which he will flow test before sending. I think I'm getting close to getting a smooth running car again! Just wanted to update you guys. I hope to update you once more saying that I'm cruising.

have to be careful with these old injectors, just sitting on the shelf for a couple years will cause them to seize up so i always test them before assuming they still work.

luckily they are cake to get to on the non turbo engines.

Totally, I was reading the manual and it said to remove the whole UIM, throttle body and all, remove air box,.. Basically just unhooked the air box hose and I was there. haha.

I've been doing this for 12 years and this is the first time ive ever run into one of these injectors being seized up from sitting, either in a car in the junkyard or on the shelf for four or five years. It was a bummer that the first pair I sent him had a dud. It is however totally possible. Not a problem tho, I've got a huge bag of those suckers and am testing for a good spray before i mail him another set.

now you know.

What a horribly unnecessary and trolling comment. Good job, buddy!

Final Update (Sucess)
 

So here's my final update on the mismatched injectors.

Acesanugal was awesome enough to send me 2 more injectors that he tested once again and this time bought some carb cleaner to make sure they flowed. I got them today and dropped them in and I'm golden! I got a very very very small hesitation when I first took it over 4k but almost non existent. I got on it again in the next gear and went up past 4k with no hesitation at all. Drove it around for a few minutes to just warm it up and got on it one last set of times and there's still a tiny tiny hesitation when the injectors kick in but I'm talking like, feels like I let off the gas like 1% throttle and immediately back on. No hesitation like would get with the wrong injectors thought. This is 99x better than when I bought the car.

I imagine the hesitation that is left could simply be because of the different ages of injectors and some may be dirtier and spraying better than others. I'll run some fuel injector cleaner additive for now but I'm going to send them all in to get ultrasonic cleaned very soon.

thanks again, Acesanugal and everyone else that helped guide me. Brappp!!

the transition hesitation is due normally to normal age related items.

1) high resistance to the fuel pump causing voltage drops and volume/pressures with the pump output

2) high resistance to ground terminal at main engine harness to rear rotor housing, this is where your injectors are grounded to through the ECU, poor connections here or within the harness cause the injectors to become laggy.

3) low main harness voltage through the main relay at the driver side firewall. this relay provides power for everything on the engine and ignition system. bad contacts could cause low voltage and poor performing electronics.

4) dirty and semi clogged injectors, even if they aren't the secondaries the primaries can cause transition issues if they are semi clogged and imbalanced.



there's plenty of other causes but these are probably the most prevalent.

as you can see, the common theme is with poor wiring which tends to cause plenty of issues with these cars but it is not always the only cause, things like simple worn out spark plugs or improper timing can make it appear worse than it should be.

Ah! Yeah, Acesanugal mentioned basically the same thing to me. He said it's due to age and is expected to feel the transition even a little bit. I owned an S5 in the past, but I mainly had my GF at the time drive it and I don't remember feeling that, maybe it was a slightly better design on the S5's, or maybe it was because it was ported? Who knows. I also had a Turbo Rx8, but clearly that wouldn't have been an issue on a new car.

Either way, I have re-grounded the car/battery, I did this as the first step before I started to troubleshoot the rest. I think my next thing to do is just take all 4 injectors in to get cleaned out and remove the FPD while I'm down there. I'm in Arizona and I found a "reputable place" that does fuel injector cleaning out here for $18 on OEM injectors (AUS Injection). I'm gonna give them a shot.

Thanks again for your advice, very insightful

I recommend witchhunter performance for injector cleaning.