Injector Question

[AJT944]

Just looking for some advice...

I've got a misfire on cylinder 1 that only occurs when I rev over 4k RPM. Starts and idles fine, and then once I go over, it misfires and never recovers. I believe I've narrowed it down to a bad injector (Swapped the injector and the misfire moved to that cylinder).

I'm just curious - is this a symptom of a bad injector - if it gets overloaded and then just stops spitting out fuel? Is it clogging after getting more flow at a certain point? Should I buy a new one or try to have this one cleaned and re-worked? Or - is this something entirely different and I'm missing something?

Remanufactured injectors are cheap from Pelican, so I'm not opposed to that.

1986 NA 944 5-Speed
I've Replaced the Following:
Fuel Pump and Filters and Fuel Rail and Lines, Fuel Pressure Regulator
Vacuum lines, J-Boot, AOS Seals and Hoses
New Idle Control Valve and Hoses
New F9Tech DME and MAF
New Water Pump and Timing Belt
New Cap, Rotor, Plugs, and Wires
New Coil
New Battery



Thanks!

[Monkey Wrench]

I cleaned my volvo ones, and made tread here :
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/1145509-cleaning-your-own-fuel-injectors.html

there are little filters just inside where fuel enters I left mine alone but they are cheap. I found that when I backflushed them, they were not clogged.

Id check them visually first by unplugging th fuel rail from the manifold so I could watch them spray while cranking and see if they all shut off, but if you do that be very careful and dont do it inside your shop and have an extinguisher that's appropriate for a fuel fire there in hand and at the ready because any little spark, and you have a big fire that's hard to put out.

sure you can buy new or rebuilt injectors is you like. Im curious how you are detecting this "misfire"

i dont know if high revs could cause misfiring and that relating to the injectors. Im not sure if thst theory holds water..

Id suspect that if you had a partially plugged injector, it will need to use more fuel at high RPMS and then maybe thats when they would be restricting ( because of the higher fuel flow)

in my thread, you can see the bottle i made up to pressurize cleaners and put them through the injectors. It worked well and I could observe the spray without someone else at the key and do it outside away from things in case of fire. I have seen some videos where the guy simply connected the injector to a can of cleaner spray ( maybe sea foam spray) and used a 9V battery to open the injectors. id just pulse the injectors, do not connect them and leave them in case you burn them out, normally they see very short pulsations.

I actually thought Id make a tape deck motor run a cam with a switch so I could vary the pulsations y moving the switch around with the idea I could then see it work with a pulsating 9V.. the Thing I built to do that seemed to run too fast and the injectors could not keep up to the very short pulsations. in the end I just tapped the wires together to create a pulse..

I went looking for injector cleaner, I found some for diesel injectors, not for gas ones, I used sea foam first then carb cleaner , my theory was the carb cleaner has a bit of lubricant. I think you can connect a pressurized can of injector cleaner into he fuel rail and flush that through without removing them from the engine. there my be an appropriate injector cleaner product. I htink on Utube they guy used brake parts cleaner.

you can check but I think the brake parts cleaner I have is non flammable so there may be more safe products. I think it removes any lubricant. shops or injector cleaner places probably have better injector cleaner equipment. Ive heard of making them out of a hydraulic jack so you control the spray by manually moving a piston basically.. that's probably a safer way, you don't want to spray any cleaners in your face especially your eyes. so please use your own judgemant and work safely.. think about any fire risk before you go spraying fuel around. atomized fuel might actually explode never mind a fuel fire.. so be careful and be very aware.



you can put sea foam or injector cleaner in your fuel tank but its hard to see an immediate reaction..

you can check your fuel flow, there are notes in the manual with the flow rate spec so you can figure out if it's adequate..

to measure what it pumps in 30 seconds or so. be careful because the fuel pump can move a lot of fuel very fast. if you have low flow , possibly could be a plugged fuel tank strainer or plugged fuel filter..

you can get node lights to plug between injectors and wiring, (Id like one or maybe 4) then it would be easier to see if one isn't getting its pulse.

if you pull injectors replace at least the O rings, I'd order the kit with pintles , the little washers O rings and the filters, they are all very cheap parts.. and I'd oil the o rings so pushing the fuel rail on isn't a struggle possibly causing you to bend it or something. there is a special little tool to remove the filters. I figured I might try to use a sheet metal screw and vice grips holding it..

id be careful handling the injectors, if you look at the pintle there is a little needle there poking out. if you drop them and or knock that needle it might do damage.

ok that's all I know ;-)

[Matt at Pelican Parts]

Very informative thread Monkey Wrench! Thanks for sharing

[AJT944]

Wow. I feel like such a dummy. The connector wasn't fully seated on the injector. Car runs great. Lesson learned- make sure the connectors are actually connected.

Thanks for the help though guys!

[Monkey Wrench]

happy you found it ! have a great day !