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fuel pump or chase ecm inputs


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2004 response lcr (320 hp) multiport fuel injected (mefi4 i think).

runs swell for very short period of time then limp mode to stall or just straight to stall.

typically restarts for a short period of time and, on occasion, no start. when it's running it's running great; no stumble, good power. no so much when the fault surfaces: either limp or stall. this rig has been running great for about 30 hours this season. fuel tank is full (visual check). new fuel filter in april (20 hours ago). new cap and rotor at fall lay-up (30 hours ago).

throws trouble code 81 "When a DTC 81 is flashed out using a Diagnostic Trouble Code (DTC) tool, a scan tool MUST be used for further diagnostics. DTC 81 has multiple failures, and are only distinguished using a scan tool" per the manual. i don't have a scan tool and the service shops in the area are in the multiple week wait times.

i started chasing gremlins at the fuel pump thinking that if oil pressure (or any other sensor) was intermittent and causing ecm to drop the fuel pump relay that lack of fuel could be a starting point. metered the voltage to the fuel pump while in a run cycle. key on powers the pump for 2 seconds then shuts pump off. pump power is present upon engine run but is no longer present upon stall. this could be a normal outcome if the ecm has commanded the pump to stop.

removed the +wire from the fuel pump. powered the fuel pump power from Vbattery. pump whines, engine starts and idles great for a bit then stalls. fuel pump is still whining after the stall so my take is that the pump is still spinning. now i know a spinning pump does not mean that i have 60psi of fuel pressure.

i was heading to the auto parts store to buy a fuel pressure test set when i got thinking about that limp mode. if fuel pump is intermittent the ecm just doesn't know that so ecm isn't commanding limp mode because of low fuel pressure, right? i'd rather not drop that $50 on that test set if i don't need to (but will, gladly, if it's going to fix this sick puppy.

so i guess that my question(s) include:

  • is fuel pressure check next on the list of things to do or am i better off metering each of the ecm inputs for normal range operation?
  • is dtc 81 an indication that something common to multiple sensors is wacked (a professional term)?
  • which sensors can cause limp mode AND stall?

thanks for reading this novella.

Edited by tvano
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Multiple codes can be triggered by a low voltage situation, what is the condition of the battery? Grounds on the engine and battery, clean and tight?

If you know the fuel pump isn't getting power when it starts to stall, you know the fuel pressure is going to drop at the same time. If you want to check it at key up (good idea) all the local auto stores should loan you one for free w/ deposit. I did this last year at autozone, and it was a real nice pressure tester, not some $50 job.

Limp mode can only be from oil pressure, engine temperature, and transmission temperature.

Have you tried playing musical relays to see if that may be the problem?

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voltages appear, at first blush, to be normal. 12.5vdc w ign off. slightly less w ign on and 14.5 w engine run.

liked your musical relays idea but it had a nasty result. that's right 99response, this must be all your fault!

went from a 'starts most of the time then stalls' to a no start.

swapped back to the original relay assignments and i've still got a no start.

checked out the schematic and started taking measurements at the circuit breaker then on to the three fuses (circled in yellow).

fuses.jpg

now it gets wierd...fuses are all fine. 20A BAT is +12v on each side of the fuse. normal. that's good.

the other circuits are at 0vdc on both side of the fuses unless i remove the fuses then i have +12vdc on the red side (normal) while the fused side is at zero.

stick the fuses back in and i'm back at zero on both sides! now i'm thinking that there are no other explanations other than an iffy splice or two between the breaker and the fuses, right?

i really, really hate to ripe the engine harness apart but i really, really, really don't like missing sets, too.

the dealerships are backlogged this time of year until - oh - february???

so i spend three hours ripping, swearing and sweating to remove an unbelievable amount of tape from the corrugated tubing trying to expose those splices.

i mean that the harness protection is substantial. more substantial than i am. i finally decided that i had to have had my head up my ... to rip this pretty harness to shreds. i'm worn out, beat up and run down. decide to trim the excess tape and pin things back together and quit for the day. i'm pooped.

all said and done it runs beautifully. i've got 10 run cycles and 20 minutes of run time in the driveway and she never missed a beat.

i'm guessing at this point that i was right to rip the harness; i just need to finish the job and find the intermittent splice(s).

just has to be. i'm not a happy camper.

edited to embed image.

Edited by tvano
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Uh oh, guess I'm in trouble.

Those are the worst problems to find for sure. Moving those relays around obviously killed the lousy connection.

Good luck finishing up the job

-Chris

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Uh oh, guess I'm in trouble.

Those are the worst problems to find for sure. Moving those relays around obviously killed the lousy connection.

Good luck finishing up the job

-Chris

mayhaps it's time to shop for a new rig.

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I'm trying to figure out what about the harness may have been whacky. You un-did the umbelical? Glad it's running good. But like you said, very wierd. You sound like a great technician !

Steve B.

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I'm trying to figure out what about the harness may have been whacky. You un-did the umbelical? Glad it's running good. But like you said, very wierd. You sound like a great technician !

Steve B.

someday when i grow up i'd like to be a good tech. no where near that now.

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the saga continues.

decided that an intermittent failure had to be chased and can not explain the voltages at the fuses so i waded back into that harness convinced that i had a loose splice.

well, BIG props to indmar. that harness is bullet proof.

Bigger props to indmar on the splices. VERY good stuff. i could not have done better myself. major splice is crimped very solidly, SOLDERED then shrink wrapped using shrink that has a melting liner to waterproof the voids. again, props to indmar; very nice stuff.

harness is back together and i still can't explain the absence of voltage at the fuses. can only be operator error but i was so very baffled that i rechecked the work about a dozen times.

wrapped it up, pinned it all together and am sitting in the driveway next to the little girl that is just purring.

i don't trust her as far as i can throw her. she may look clean...

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chased down a tech1 scan tool. dtc 81: "inj a low/open and inj b low/open"

dealership techs (were very helpful. props). said that this is a bs / catch all dtc. seldom see any injector problems and when they do fail it's a fail.

this code is more likely indicative of a low voltage (loose, bad ground, etc) or, on occasion (seldom), the tps may be noisy.

was seeing "oil press" and buzzer on occasion at tip in and oil pressure gauge was bouncy so i bought both oil pressure sending units (gauge and ecm feed) and tps.

cleared codes. going to float today w crossed fingers. bummed that i have not found a smoking gun.

i've got the tech1 in the boat along w a volt meter; ready for the next go around.

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Yeah the injector codes confirm my original thought of low voltage, I've never seen an injector fail but have seen plenty of codes thrown.

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starting to tick me off. what good is a boat that doesn't run?

after oil pressure sending unit and tps a 1.5 hour shake down cruise was sweet.

then i picked up my partner from the dock and 10 minutes later the tps died (per tech1). wag: infant mortality.

replaced tps w a new unit and headed out today for another 2 hour shake down cruise. all is swell.

pick up my partner from the dock and head down to the course. drop in and it won't start!

dtc 81: "inj a low/open and inj b low/open" typically during idle. cleared codes but she stalled a dozen times through the sets.

always restarted and got us back to the ramp.

i've been through the grounds and battery terminals. all are clean and tight.

i will go through all of the grounds and junction blocks again tomorrow to insure all are clean and tight.

a new observation: typically key on without engine run nets a periodic (1 sec?) warning buzzer.

upon stall at idle the warning buzzer does not sound until gauges reset and at times that takes 10 to 15 seconds.

after the periodic buzzer returns then the engine will typically crank right up.

if i don't wait for the buzzer to become periodic then engine run isn't likely.

what signals does the mmdc supply to the engine? could a sick mmdc cause this type of problem?

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The two injector circuits (a & b) are fed by with a constant hot +12 volts via the fuel inj fuse and the ECM relay. The circuits have two individual grounds whiched are controlled (pulsed) by the ECM. Check all the +12 volt parts of the injector circuits for loose connections or possibly a bad relay.

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Have you checked all of the connections behind the breaker panel/below the shifter?

spent the morning pulling the drivers seat and yanking the panel to check things out.

nothing seriously loose except the crimp for the docking lights.

touched all of the buss bar fasteners. re-crimped all of the crimp-on connectors just to be safe.

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The two injector circuits (a & b) are fed by with a constant hot +12 volts via the fuel inj fuse and the ECM relay. The circuits have two individual grounds whiched are controlled (pulsed) by the ECM. Check all the +12 volt parts of the injector circuits for loose connections or possibly a bad relay.

tugged and wiggled each of the injector leads and connectors while the rig was idling.

same with the ecm connectors. at this point in time i'm hesitant to rip that harness apart (again).

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i tugged and pulled my way through the harness while the rig was running.

she shut down when i got to the harness v relay interface at the ign. relay.

swapped the starter relay with the iffy ignition relay (a suggestion by 99response oh-so-long-ago).

(in all fairness; that is when i started down the false path to a harness problem. still a senior moment on this end, no doubt).

ran 4 sets on wednesday without a shut-down event.

fingers crossed that the gremlin has gone away.

new relays will be here first of the week.

props to 99response.

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Ted....behind on posts so just getting caught up. I used to have a Tech 1 and we probably still have one laying around somewhere but sounds like you got that covered.

If you're still stumped on this, if you find yourself in a stall and no-start situation, try removing the connection from the fuel injectors one-by-one and see if you get a re-start with one unplugged.

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Ted....behind on posts so just getting caught up. I used to have a Tech 1 and we probably still have one laying around somewhere but sounds like you got that covered.

If you're still stumped on this, if you find yourself in a stall and no-start situation, try removing the connection from the fuel injectors one-by-one and see if you get a re-start with one unplugged.

good thought on the injectors. thanks for the tech1 offer, got it covered.

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i've had no problems since swapping out relays (about 13 hours of run time).

i've replaced that intermittent relay with a new unit; still healthy.

while only time will tell if this intermittent problem is really gone i've got a pretty solid feeling that the relay is the source of my problem.

thanks for all of the assistance; all good directions to turn.

thanks for this bbs; it's a great resource.

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