Help wanted: 87' 944 NA dies when connecting all 4 fuel injectors

[PrincessNara]

Hi, i've been having an issue with my 87' 944 NA, If i plug in the wiring to all 4 fuel injectors the car loses spark and dies, I have replaced the fuel pump, pressure regulator and damper, injectors, and injector wiring connectors, I have also replaced the capacitor in the DME and tried two different ROM chips. The car runs fine (aside from only using 3 cylinders) if i disconnect the wiring to any of the fuel injectors. I'm out of ideas for what to try next aside from buying another DME to test with but they're pretty expensive so i'd rather not if i don't have to. I have also checked the ground for the injectors and for the DME and they're fine. If anyone has any ideas please let me know, thank you!

[New2me944]

When you changed the injectors, did you use aftermarket ones?

[PrincessNara]

Yeah, they're aftermarket but they match the stock ones, resistance measures the same

[New2me944]

The reason I asked is because your situation reminds me very much of when I got my 944.

The previous owner had done some work to it, including new injectors, and it would only run on three cylinders. Moving the injectors around to different spots on the fuel rail made no difference. The same cylinder always misfired.

My brother had a non running 924 of the same year with the original injectors, so on a whim we pulled the injectors from the 924 and installed them in my 944. The car started and ran smoothly with no hint of a misfire.

I'm not sure what was up with the "new" injectors but swapping them for originals fixed the problem.

[PrincessNara]

I'll give a different set a shot, i replaced the original ones because one of them had failed and they weren't in very good shape

[originalowner]

Check your fuel pressure with a mechanical gauge at the injector rail. It is likely too high.

[wwdwgs]

take a look at this :
Boschhttps://www.********.com/en/moreinfo.php?pk=280509&cc=0&pt=6224&jsn=3&_nck=%2BrD%2FS8XUfCA68%2FqF15iuLEyAzia5s9QZyxv%2BU XBFCAb4Zbw4JRTIIM9VhrwLhFkv1gSyN9rSd7VdA2mv2pZ1ELx RZmxeOlQrKXVceuk0ZowEZlDkXtkP7byKy8GVP7NIBafx%2BMo pfMrJSfdYMqt2qRXLFq0elS%2FX%2B1I%2BUVDhYOEjXbbDBL9 R970H1fKcnmMFraaxO2zc5M5dzTGFG8UYZYdcfflSAMN2fTKOZ znzV%2Bg%3D

Modern Injector that replaces the stock injector. Requires 3 Bar Fuel Pressure Regulator

[wwdwgs]

That is from RA

[Jfrahm]

I checked out some inexpensive new aftermarket injectors in the past and found them to be way off in terms of flow. I agree, try some genuine stock injectors.

[PrincessNara]

I'll try some if i can find some that arent too expensive, my old set had one that was completely dead and they'd started to get rust on them, checking in with a couple breaking listings locally to see if i can get some, will test the rail pressure on tuesday cause i need to get a tester

[Jfrahm]

You could put your old ones in with 1 new one and see if it runs better. Or with the fuel rail out put cups under them and compare old versus new fuel volume after cranking a bit.

[New2me944]

You can recondition your old injectors by using the process outlined here.

https://www.pelicanparts.com/techarticles/944_fuel_injector_clean/944_fuel_injector_clean.htm?srsltid=AfmBOoq9hgj9rL O97WdoJ682fHcf9KuQZUH58iLK2hLTO0ipfr0_L98t

[Monkey Wrench]

ok heres' what I do but recognise that spraying gasoline around can cause an explosive conditioner so you must take steps to be safe, dont do this in a shop, have an extinguisher ready, prevent any sparks, think about your safety and do not proceed if you feel you are putting anyone in danger.

Just becuae I do this and took soem photos, does not mean it is smart or safe!

you can also conect a guage to the fuel rail and check to see if the fuel rail holds pressure. - withoug spraying gasoline , this is more safe.

when flushing them wiht the bottle I do it outside, cleaners vary in flamability, you may choose brake parts cleaner, some cleaners may be less flamable but do your own safety checks and think the process through before endangering anyone..

I like to see them flow and then I can observe the spray pattern.



yes order the seals the little washers. I believe there is a screen basket you can look into the inlet of the injector for it. I backflush first and did not find any that were plugged up , left them alone then.

I made up a pressure bottle , trigger the injector with a 9V
or check them right on the engine.

I found a little bottle wiht a cap rated for 100 PSI it has a small cap I can remove to fill bottle.

I fill bottle with carb cleaner about 1/2 way
presurize bottle 50 PSI max
install injector , tighten hose clamp.
open the tap on the bottom to expose injector to pressurized cleaner. spurt the cleaner through with the 9 V in short bursts.

- backflish and verify good flow.
- make the injector spray so you can see the stream looks normal.
make sure the pintle caps are snapped on properly. use new O rings , 2 per injector.


2nd method, put shop cloths , remove injectors fromt he block, reconnect wires. spray injectors by cranking only for a short burst, check spray pattern on rags. - if an injector will not shut off it may not close, check that they all close and do not drip after key off.
recognize that the atomized spray of fuel is not only flamable but may be explosive and there are dangers , which is why manuals will not recomend this.

- ONLY CRANK ENGINE FOR A SHORT BURST !

Note how how the patterns left of fuel spray are roughly similar in size and none continue squirting or drippoig after key pff

the injectors can be sent in for testing in a more safe way with better equipment, and this is likely a lot more safe.

photos are of a volvo , not a porsche 944

also I have in cases found it took incredible hand strength to reseat the injectors so here's how I do it, If it seems a struggle for me.

use new Orings every tme, never reuse them. lube them up before insertion.

to install on fuel rail ( before removal note how they all look so you know how far they go into the cups. )
I tie the injector to the rail with a boot lace. I don't pull against the plastic part, or the connector, Instead I use the bulbous shape and tie a loop around the main body of the injector. then tie that around the fuel rail.


then use my hands to keep the injector straight and plumb to the fuel rail cup. while keeping the injector straight I stick a screwdriver throught the boot lace , twist it, this exherts a lot of force, pulling the injector carefully and controllabbly into the fuel rail cups.

if the injector becomes crooked or cocked, stop ! You may cause the Orings to become cocked or tucked under and then it will leak fuel.

after installation start the car, run it a very short time shut down inspect carefully for leaks.

do not go driving or run it enough to make the exhaust manifold hot before you are completely sure you do not have any fuel leaks. look at each injector carefully to be absolutely sure all are seated properly

a little cautionary tale.. ;- )
I did replace injectors in my 88 ford van 4.9L striagt six

- on that engine it is very difficult to get to , the whole intake manifold needs to be removed first.

What happened to me :

had not seated one injector into the rail properly , it worked seemingly fine ( no leaks) until a week or two I began to smell gas. I removed the doghouse to look, it was leaking a LOT of fuel because I had failed to seat one properly, it was GUSHING!

this was very dangerous and I had to take it all apart agin to correct it. - lesson learned ,lucky It did not catch fire ! good thing I dint plan a highway trip.

also if you drop an injector, it will surely land on the pin on the end of it, this will ruin it, So I suggest to lay lots of dry rags around the work area, to catch parts and protect the injectors from damage in case they are dropped. it is easy to drop them especially in a 6 cylinder. som many to allign and manipulate at once with only two hands, having a helper , to have more hands on the job could help.

before and after installing injectors in the engine what I do is find a nut the right thickness to use as a spacer, (the nut is my guage block, simply used as a depth reference) Take measurements with a vernier calliper if you prefer. take pictures.

check that they are installed to the same depth and one is not cocked stuck or not inserted fully.

the injectors on a volvo need to be grounded, and they are grounded to the same bolts that hold the fuel rail, failing to ground the injecors properly could cause a spark and they won't fire without being reconnected. I assume the 944 is similar. Id make sure those grounds are solid and not causing sparking by any interruptions to the the ground.

[PrincessNara]

I'll give it a shot, just got done getting rid of the surface rust on my old injectors, waiting on new seals to arrive in a week or two

[wwdwgs]

MW,
Your Volvo's FJ looks similar to the 924-944:

[Monkey Wrench]

the injecotrs fuel pumps and a lot of the other electrical parts are made by bosche not Porsche

some one correct me if this is wrong but you have 4 injecotrs and the car riuns with one unplugged and you have changed the wiring to the injecotrs.

are the injectors connected directly to the ECU or other witing involved in this electrical path feeding 12 volt pulses.

would that mean there are 2 or 4 oins on the ecu providing this pulse?

can PrincessNara use a scope to probe this pulse back to the ECU? or check for problems of thes wies being grounded to body?

Thing is, "I THINK" the injecotrs fire in pairs , two on each engine revolution, then the other two.

would that mean the ECU has two transistors switching on and off this current?
2 ECU pins or 4 PINS?

Eproms can be damaged by electrostatic dischearge ( static electricity)


oem ECUs ( later ones) have the abiity to use different fuel maps so there muct be a link then to the Eprom or chips to provide this adjustability.


I assume thise are low voltage signals that are in turn amplified into usable current by a transistor or something similar inside the ECU

im making the assumption that since they are firing in pairs that they are then working at the ECU level.

if you groiund out that signal maybe the ECU shuts down?

if you have i dentified the problematinc injector , can you follow its wire and maybe there is pin damage at or something wrong causeing it to get groiunded out?

do the injector wires teminate at the ECU or are there other electrical parts involved?

teking your diagnosis literally it seems that unplugging one injector is causing to th ebea able to start but when plugged in it is not providing a pulse. the logical reason seems ot be that that connmector or its feed wiring is becomiong grounded and doing "bad things"




if the ECU can fire three of them and run the engine , and they are fired in pairs my assumption os tha tthe ECU is essentially working. It must be providing at least thre of the 4 pulses and if thye fire in pairs ell im not sure where or how thya re separated or if they are simly wired in parallel wiht the transistor turnign them on and off. If it is indeed one transistor for the pair then it must be funtional?

I dont have the knowledge to go deeper. others here may.


what you seem to repoert is that you have a pulse for 3 of them. you connect the 4th and it wont start..

Just a theory but im thinking this wire although replaced is somehow grounded, so when you plug it in( the problem one)
- It is then shorting things out and maybe the ECU shuts down the ignition or injector pulse .
so question - are you gaining and loosing the "ignition pulse" by doing this?

suggestion:

if you put a small bulb across the coil, ( the spade terminals) it shoudl flash with engine cranking, the bulb is now wired in parallel wiht the coil's primary winding.

Id use a small bulb like for a dash lamp etc. leave it connected so you can observe if you ave a ignition coil pulse as you are experimanting.

I suggest put a test lamp there, if it is flashing you probably have a spark if not you do not have a spark. . With that bulb connected you can try starting under different conditions and see if one condition seems to change weather it has an ignition pulse or no pulse.

If the promary has no pulse you have no spark either. I think you may watch that bulb flash during cranking as you do different things. it might shed a clue?

if the primary coil has a pulse the ECU is understanding the pulse from the TDC sensor and speed sensor , it needs those inputs to make a pulse . If the primary coil has no pulse you have no spark and the engine will not fire.

if you start the engine the bulb will flicker so fast it will just apear to be dimly lit because the bulb takes time to heat and cool its filament. obviously if it is runing you have an ignition pulse.



maybe you could try to see if the pulse disappears under different conditions such as the bad injector being plugged in or disconnected?

i suppose one could probe that injecotr pulse with a scope and see the trace, that might be helful in diagnosing it.

if you can determine which ECU pins are involved in the injector pulse maybe you can examine them for pin damage. have a close look for a pin that got bent over?

the DME relay provides fule pump power but also DME power, it is a double relay. ids it possible the ECU is not getting consistent power> is the ECU's groiund reliable?

maybe you can put a test lamp on the ECU power input from the DMe relay and watch that bulb to see if the power to the ECU ois somehow inter=mittent, the relays, when contacts etc wear, can cause intermittent conditions.

what pins feed the injecotrs? are there two pins or 4 pins used? if the injectors are firing in pairs you only really need two hot wires right?? - ill leave that open to question.

[PrincessNara]

I've tried different eeproms, i have two that work to test with, the ecu can fire any 3 injectors and to what i recall on this car the injectors are driven in pairs from the ecu. The car loses spark when the fourth injector is connected, but it works with any 3 injectors not just one specific one unplugged. the DME relay has been replaced and i've checked the grounds for both the dme and the fuel injectors, the DME is shutting off the car (no spark) because it's detecting that something is wrong, i just am not sure if its correct in saying something is wrong, will be testing fuel pressure soon when my gauge arrives. I dont currently own a scope, also the connectors arent grounded anymore, tested with a multimeter

[Monkey Wrench]

Originally Posted by PrincessNara

it works with any 3 injectors not just one specific one unplugged.

plugging in the 4th one , assuming they are parallel would mean you have lower overall resistance, higher amps. more circuit paths.

maybe the ECU isnt; liking the amp load and some internal protective electronic mechnism mechnism is shutting it it down?

i believe some components exist that work as basically a self healing fuse. overload them and they open.

I do not know if the ECU could incoportate such a protective electronic mechanism.

any variance at all in the resistance through various injecotrs? lower resistance may mean the board is handling more amps. lower resistance= increased curent flow.

is it possible that a coil of wires, ( the electric solenoid in an injecter) has an internal melt down , or corrosion, then it may have lower resistance beacuse some of the turns of that coil have become shorted?

possible wrong injectors installed, new ones installed , with not enough resistance, overloading the amps available? ?

I suppose you can lower circuit resistance by adding resistors in serioes with injecotrs, maybe so , but it sounds like quite a "kludge".

[PrincessNara]

they have the same resistance as the old injectors, also getting a little over 2.5bar with 3 injectors plugged in at 3,100 rpm (for some reason that's the idle and i have no idea why)

[Monkey Wrench]

Originally Posted by PrincessNara

they have the same resistance as the old injectors, also getting a little over 2.5bar with 3 injectors plugged in at 3,100 rpm (for some reason that's the idle and i have no idea why)

Im wondering if th esame problem ocurrs with the older injectors. Understandable a bit of work to switch them out again.

very fast idle, coudl there be a manifold air leak? I guess yud want all the injectors employed before worrying about idle speed but it does seem extremely fast.

I don't think the fuel system has any more input than the vacuum line, but if there is an idle air control valve maybe its; involved perhaps that could affect idle speed.

any fuel in that sensing line could nean a ruptured fuel presure regulator diaphram. maybe that scenario could pull in unwanted fuel through that line, Id unplug it and have a sniff , see if the line smells of raw gas.

I find it hard ot trll if an idle air bypass is open so Id try to study that ( when it is powered) with a small test lamp so you cna keep an eye on that while experimenting.and know in real time , if open or closed. easy enough to bench test them, bow though it while feding 12 V,

In volvos some have 2 wires, some have 3, alos some have 3 hose connections and some have only two.

It could be a part shared with Volvo 240 0r 740.. . there are some different ones but I swear ai saw a list that showed at least one, as beoing common between some 944's and some volvos.
you can clean them but keep the motor at the top youdont want cleaner in the motor, it is a motor but one that only turns part of a revolution
Ive noted sometimes they buzz a bit, never knew why.

I gutted one to have a look inside, it didn't seem worn out of clogged up. but I guess it could clog up.
I didnt; feel it ever completely seals but when open has little restriction. when closed has some amunt of bypass because its; not a tightly fitted valve.

Id check any hose that conducts PCV fumes they tend to rot from the exhaiust gas residue. also vapor cannister system or the hose connections may leak and contribute to extra inlet air
the vapor cannister runst to the manifiold somehow. the other side is connected ot the tank and I assume the gas cap seals it. when the tank gets warm the gasses need to exit somehow so they can leave through vapor cannister to be reburned.

i tmight have a rubber line back to the tank so it can vent this way, those lines could perhaps rot out from fuel vapors. might be plastic and ok? maybe you can pinch off thatmanifold line to se if it affects idle when it is closed off.


it sounds like the main mistery is why the heck it runs wiht 3 injectors but fails to start with 4. Im afraid I do not have a valid answer to that. and it bugs me ;-)

can injector resistance be checked back at the ECU? it would then include the wire runs.

I know in the volvo tune up info the resistance is checked through the idle air bypass valve from further back in the harness and they specified an expected resistance.

maybe others have better suggestions on what to do next. lets wait and see.what others may offer.