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Need advice from experience for an M42 rebuild

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  • JonsE30
    replied
    Thanks bmwman91 i will bust out the meter and check on these. i've come this far so i can't give up yet.

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  • bmwman91
    replied
    I believe that code 1252 is caused by an electrical fault where the Motronic detects that not enough current is drawn by the injector(s). The mid-current driver IC in the DME provides a feedback signal to the controller, and the ones for the injectors seem to need to detect at least 1A of current being sunk (IIRC) in order to signal proper function.

    If all of the injectors are barely spraying any fuel, then there is virtually zero chance that this is a fault with the injectors themselves since they are not all going to fail at once. What voltage do you measure at these 3 locations, after putting the key into Accessory-2 position:
    1) At the fuel pump across the power input terminals
    2) At the injectors (if you pull the electrical rail and probe between ground and the terminals for the injectors)
    3) At the power distribution block on the firewall. Not on the large lower part with the ~15mm wire, which is for the starter/alternator, but on the smaller lug above it where a ~5mm black wire connects. This is a separate wire run from the battery which is for the injection electronics.

    If it all reads normal when just sitting in accessory power mode, then you could try #3 while a buddy tries to start the engine to see what it drops to. I am guessing that you are seeing a power brown-out in the injection circuit due to corrosion or fatigue on the ~5mm wire, about 15" forward from the battery where a 50A fusible link is installed on it. It is notorious for seeing failures at the crimp connections and causing really stupid, hard to resolve issues like this. That is, if you have an iS with the battery in the trunk...sedans with the battery under the hood didn't have it.

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  • JonsE30
    replied
    some busy weekends lately but got a chance to try that test that roguetoaster and try to put water bottles under the fuel injectors and try to crank and see what happens. i tried cranking it for a bit and it didnt spray a lot of fuel out. i tried cranking again, then took out the water bottles and its like a few droplets. i put a dry rag and laid it like a blanket under all 4 injectors and cranked again and it's faint discoloration from fuel. like its not spraying, more like trickling? i still get code 1252 doing the stomp test.

    does this mean my injectors are bad? the condition is unknown, i mean when i pulled them out almost 2 years ago when it still was running, then cleaned them before i put them back. could code 1252 mean a bad injector or is it like the wiring for the pulse trigger bad?

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  • JonsE30
    replied
    do you spray starting fluid in the throttle body assembly when throttle is open?

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  • Victell
    replied
    Sometimes Ill use a couple sprays of starting fluid to see what happens.

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  • roguetoaster
    replied
    You can take the injector rail assy out, place each injector in a bottle and crank once you disable the ignition system for safety. This will clearly show you any faults.

    Are the injectors unknown or known working?

    You can also clean injectors to some degree if it comes to that.

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  • JonsE30
    replied
    thanks for the advice guys. i got some free time while the kids were away. i unhooked the fuel lines and reversed them back. there was a little bit of pressure in the lines so i tried to keep a rag there from preventing it getting everywhere, but there was still some light splashing. i wiped off as much as i could then let it dry for a few hours.

    i plugged the battery back then tried to start. it turned over but still didn't catch. i did the stomp code again and the 1216 tps sensor was cleared now, but now i got a 1252 which i researched is fuel injector #2 issue. one of the threads said it was due to no current/voltage going to that injector, but i tested it with the light tester and it was fine. does it mean the injector itself is bad or clogged? is this enough to prevent the car to start?

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  • JonsE30
    replied
    Thanks so much. I'll check that next!

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  • roguetoaster
    replied
    The hose that comes from the top of the tank to the fuel filter can be replaced if you just lower the tank.

    You need to verify fuel supply at both sides of the fuel filter then at the connection to the rail. If you have it to the rail but not at the rail you have the supply and return lines crossed.

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  • JonsE30
    replied
    pulled each spark plugs and cranked while it was sitting on the intake manifold and all showed Sparks. when I pulled them they all look wet with oil probably from when I tried to prime the engine for the first time during the first cranks with no fuel. the fuel pressure regulator has the vacuum hose attached. more troubleshoot I've done: so I took the upper intake off and pulled fuel rail out. I bought a circuit tester light to check for power. I took off each injector off the rail expecting fuel to leak out but it was dry. I tested all 4 leads and they all have continuity. the fuel hose for the return line was the one leaking from the clamp so fuel was at the rail. i tried cranking without the injectors on to see if fuel would come out the 4 holes out of the rail but nothing came out. I am so confused. if there was fuel in the return hose, is it safe to assume the pump gets gas to the feed line through the rail and back to return line? I checked again under the car and the hose that connects to the back of the fuel filter up through a hole in the chassis then what looks to clamp to a hard line near the top of the tank is leaking. there is foam around that clamp and it's damp and soggy. do I need to drop the tank to replace this hose? I am so lost. can this leaking fuel hose be the cause of all the fuel supply issue at the rail and with the injectors?

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  • Victell
    replied
    A few things I would check:

    - Make sure your fuel pressure regulator has the vacuum hose attached.
    - Check to make sure you're getting spark
    - Pull a couple spark plugs and make sure they are not wet with fuel, could be flooded.

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  • JonsE30
    replied
    Did more research and found out the fuel pump doesn't "hum" in there cars. I took off the upper intake and the left one on the black hard line was seeping fuel when it flexed a little bit so I clamped it down. But that tells me the fuel pump is working and getting to the rail. I got under the car and checked the lines again and it looks like there is cracking on the hose from the pump to the rear of the fuel filter. I pulled up the rear seat and checked the pump and lines there and no leaks but I'll need to fish out the bad hose and get a new one in there. Still no start so do you think it's the fuel pressure regulator, injectors, wiring harness, crank position sensor?

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  • JonsE30
    replied
    found out the main wiring harness was not fastened all the way down so the pins were not making contact with each other. i sorted that out and all the relays clicked and the i was able crank and pump the oil until the light went out. i then put back fuse 11 and fuel relay and tried starting it again. it did not start but now i found a little puddle of fuel under my car and it was coming from the fuel filter? could this be me mixing up the fuel lines that go into the fuel rail? UPDATE: I checked real OEM and my fuel lines are going to the right peg on the fuel rail. I tried it again and it only leaks as soon as the engine cranks. I didn't touch the fuel filter or pump during my rebuild, so I'm not sure if I messed up anything hooking up the lines under the hood?
    Last edited by JonsE30; 02-01-2020, 06:55 PM.

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  • JonsE30
    replied
    so i thought i double checked everything, i filled her up with oil and filter, pulled out spark plugs, fuel pump relay and fuel pump fuse #11 and tried to turn her over to pump the oil but i got nothing.

    the dash lights turned on, radio turned on, headlights work, but the power windows controls don't work and neither does the heater controls to turn on the fan or a/c.

    i dont know much about electrical, i just put everything back where it was unplugged from. could it be the starter? alternator?

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  • JonsE30
    replied
    Got it. I got new stuff under the intake, put the lower and upper intake manifolds, injectors and rail, throttle body, air box, valve cover and spark plug. All the connectors had a home so nothing is just dangling. I am about to get started on the cooling system stuff now. Once everything is back on, I assume I refill all fluids like oil, trans and coolant and take out flywheel locking pin. Is there a checklist I can go through for the 1st start? I don’t wanna mess up after everything up to this point. I read I remove fuel pump relay (the middle one in the harness on the firewall I think) then turn the key and everything turns on and it’s supposed to turn over to pump the oil until the oil pressure light goes away. Am I supposed to leave the spark plugs in during this step? Lastly put back the fuel pump relay and then turn the key and it should fire up?

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