ASenna Posted April 29, 2009 Share Posted April 29, 2009 First some specifics: 75 280Z with L28ET running on Megasquirt II. OK so before I bought the Z, I knew it needed a fuel pump. This was evident from about 5 weeks before I bought the car when Tony ( Tony C ) lost his alternator and the fuel pump starting making loud noises ( maybe from voltage drop ruining it...I don't know ). Another habit the car had as of recently was blowing the fuel pump fuse ( which subsequently stranded me about 25 miles from home ). So I got the new fuel pump last week, installed it, and the car ran fine. Pretty decent I might add ( not that it ran terrible before ). However, it needed a jump to start ( odd ). Took her down the road. She ran a little lean, but with definite fuel pressure ( something the other pump didn't have ). Maybe it was just the difference between the pumps and I need to mess with the regulator. Anyway, I get back in my driveway and start rolling down its 200 foot length and it dies, no fuel pressure, no chance of starting again. Open up the hood, check the fuses, sure enough, fuel pump fuse is blown. The fuel pump circuit runs on its own line for the MSII system. The only reason it would blow would be something from THAT circuit. I ran the lines back through the car and couldn't see anywhere where the hot side might be grounding. Took her out of the garage yesterday to investigate again. I think I might have a vacuum leak for one, but two, once she died ( from me investigating the vacuum leak ), she tried to turn over about 4 times and then quit. No start. Not even trying, like the battery was dead. Had the battery tested today and turned out to be good. Maybe not enough cold crank amps? Any ideas? Here's the symptoms ( cliff notes of the thread ): Takes several turnovers to start, often starts and dies, sometimes when it dies it doesn't even try to turn over, when it revs up coming back to idle almost kills her ( sometimes does ), brake pedal sinks to the floor ( brake booster leak? ), fuel pump fuse blows every now and then. Ideas? Should I set the car on fire? ( kidding...but not really ) Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted April 29, 2009 Share Posted April 29, 2009 The failure to run right sounds like electronics based on other electric issues. I quickly changed a lot of wiring, power, alternator stuff on my car, so I don't recall how the exact stock system works, but it sounds like your voltage regulator is bad. It could cause a good battery to drain, kill a fuel pump or pop the fuse, maybe smoke a ignition setup, etc. Definitely the kind of intermittent (maybe heat based) issue electrical stuff could cause. Quote Link to comment Share on other sites More sharing options...
ASenna Posted April 29, 2009 Author Share Posted April 29, 2009 The failure to run right sounds like electronics based on other electric issues. I quickly changed a lot of wiring, power, alternator stuff on my car, so I don't recall how the exact stock system works, but it sounds like your voltage regulator is bad. It could cause a good battery to drain, kill a fuel pump or pop the fuse, maybe smoke a ignition setup, etc. Definitely the kind of intermittent (maybe heat based) issue electrical stuff could cause. Voltage regulator? Tied to the alternator assembly? A newer Hitachi unit was just installed because the old alternator went bad. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted April 29, 2009 Share Posted April 29, 2009 regarding the fuel pump.. I have always run a large diameter wire directly off of the alternator to a relay, and from the relay to the pump, and then have whatever you want (your MS output, or some other wire that is powered when the key is in both "on" and "start") turn the relay on. There is only power demand for turning the relay on and not actually powering the fuel pump. This way the fp has a constant voltage source seperate from other systems. Could there be some crud in the gas tank causing the fp's to struggle and eventually fail? Quote Link to comment Share on other sites More sharing options...
ASenna Posted April 29, 2009 Author Share Posted April 29, 2009 The previous owner suspected that might be the case. He drained the gas tank, took all the fuel lines down, and blew them out. Nothing. It was nice and clean, although maybe there's still something that's come loose in the tank? The tank was refurbished 2 years ago and a sump was added for the fuel lines. The tank was covered in this rubberized stuff. I'd think if it were crud, it wouldn't run up as well as it does. I started her a few minutes ago. Here's my symptoms: -Started on second try. First try, start and die -While running, the fuel pressure bumped around 40-41psi and wouldn't stay put. While bumping around, the engine rhythm went with the bump. Would rev up to 750rpm or so and drop back to 600. -Did this bumping around until it finally bumped too low and decided to die. -Started again and immediately died -Started again and immediately died again -Would not start. Would turn over forever, but no fire. Does this help at all? Quote Link to comment Share on other sites More sharing options...
ASenna Posted April 30, 2009 Author Share Posted April 30, 2009 I took Tony's advice and made a new ground for the fuel pump to no avail, but the car loped around until it warmed up and when it did, it idled fine around 725rpm and the fuel pressure steadied out to around 39psi. Something else Tony told me was to check and make sure that I was getting the right voltage out of the alternator and across the battery. Well the multimeter I have at the house I don't trust at all, so I grabbed a few 15A fuses and went down the road toward autozone. The battery tested barely over 12V in the car while on, which apparently indicates that either my alternator isn't putting out enough voltage or my wiring is choking it somewhere. They couldn't test the alternator in car, so I'm going to tear it out and bring it to them tomorrow to test. It's a remanned alt but there's a chance it could be bad already. Someone else mentioned something about the voltage regulator. The new alt is internally regulated, so that may lead back to the alt again. Oh well. It's a journey. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted April 30, 2009 Share Posted April 30, 2009 I assume you're watching A/F ratios? What are they at? I've seen voltage regs do a lot of funny stuff; when they aren't working right they can overvoltage stuff and fry it, damage it, etc. They can also go low and cause electronics to not work reliably; particularly the relatively sensitive Megasquirt. Try starting it and unplugging the battery and see what voltage runs at, if it stays running (as much as it did), etc. What do your plugs look like? Try cranking with each plug in the cable and layed out on your valve cover to confirm all 6 are getting consistent spark. Quote Link to comment Share on other sites More sharing options...
usafdarkhorse Posted May 1, 2009 Share Posted May 1, 2009 . Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 1, 2009 Author Share Posted May 1, 2009 A/F ratios are stoichiometric. I'm not watching actual numerical values, but during idle and run up the AF gage stays put with very little variation and no creeping into the lean or rich. It's very interesting considering I've seen it spew raw gas out the tailpipe while still having a stoichiometric AF ratio. Haven't tried confirming spark yet, but she runs up excellently. After talking to another guy with a boosted Z on MS, everything I've mentioned is pointing towards a lack of voltage either caused by a faulty alternator ( which is new...still could be bad ) or a ton of resistance through the board. Apparently MS will still work on low voltage, it will just exhibit the signs I'm seeing now, which was confirmed with the battery voltage being tested while running. It wasn't even running from the alternator, just straight from the battery, so I had to get it home quick. When I was having the battery tested, after the car shut off, I opened the relay board to check the fuses and the relays were HOT. Really hot. Maybe there's a bad solder somewhere. Quote Link to comment Share on other sites More sharing options...
RUZN Posted May 2, 2009 Share Posted May 2, 2009 If your blowing fuses to. Make sure the wire Diameter is large enough for the Load put on it. If its to small it will get hotter than normal causing more resistance. could just rewire the ground on fuel pump fairly easy I grounded mine to the rear of this inside of the car near the tail lights just ran a new wire through the floor hole thats there and up to the lights. as for power you could do the ame larger wire if you wanted. maybe back of fuse panel theres a junction happening allowing more Amps to get to that circuit like 20amps instead of 10amps or whatever spec is.. Quote Link to comment Share on other sites More sharing options...
woldson Posted May 2, 2009 Share Posted May 2, 2009 Ok did it. Dose your seat belt light come on? Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 2, 2009 Author Share Posted May 2, 2009 I actually don't think I have a seatbelt light anymore lol. I have 4 point harnesses and ( if I remember correctly ) the seatbelt light is in the dash around the A/C unit which I definitely do not have since I have gauges that sit there now. What's the purpose behind the seatbelt light coming on? Quote Link to comment Share on other sites More sharing options...
woldson Posted May 2, 2009 Share Posted May 2, 2009 To help determind if you are just dying, or if you somehow are going back into acc mode. Oh well. Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 3, 2009 Author Share Posted May 3, 2009 Might have found the problem. Checked the MS relay board for possible corrosion or broken solder. Tony had always suspected that it wasn't weather resistant despite MS's guarantee that it was fine to run the relay board under the hood. Here's what I found: The blue nastiness forms a perfect circle around what looks to be some white residue, which is what happens when standing water finds an electrical current. So, if the relay board is too close to the undertray, a little bit long of a solder + a little bit of water = short to ground. When looking to find under which relay this grossness belonged, it turned out to be the fuel pump relay. This might also explain why quite of bit of voltage is lost somewhere in the system. I plan on drilling a few holes in the tray underneath the relays, covering the tray in vinyl tape, and poking the holes through. This way the standing water can drain and it won't accidentally ground due to flex or anything else. Quote Link to comment Share on other sites More sharing options...
woldson Posted May 3, 2009 Share Posted May 3, 2009 Nice troubleshooting!!! Hope you found the gremlin! Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 4, 2009 Author Share Posted May 4, 2009 The sad part is that I did not find the problem. It looked promising, but it didn't remedy my problem. I refocused my efforts toward the wires crossed for the external to internal regulator swap as mentioned here: http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html Everything looks pretty good but I may just undo the connections and redo them to make sure there's no corrosion. Also, the main wire that connects the alternator to the battery is white with red stripe. It also has a crossed connection that I may check as well. Any ideas? Recap: -Low voltage across battery, starts and dies, runs lopey, sketchy fuel pressure. -Battery's good. -Alternator's good. -Thought relay board might be shorting. It's good. Keep in mind this car has ran perfect for 2 years up until 2 months ago when the old alternator blew and the fuel pump started whining along with the fuel pump circuit blowing its 15A fuse. Does anyone want general engine bay pics that might help? Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 9, 2009 Author Share Posted May 9, 2009 Update: Took a digital multimeter to all the connections of the alternator and across the battery and here's what I found: When engine's off: -12.35V across battery terminals -12.35V at the BAT connection out of the alt ( where the alt connects to the battery...this is the output connection of the alt that should be a few volts higher than the 12V supplied by the battery when running ) -12.35V at the flat part of the "T" connector ( top of the T ) -0V at the straight part of the "T" connector ( middle of the T ....this should be 0V because it is only on when the ignition is on to "excite" the alt ) When engine's on: -11.83V across battery terminals ( uh oh ) -11.83V at the BAT connection out of the alt ( uh oh...this should be around mid to high 14's ) -11.83V at the flat part of the "T" connector -11.83V at the straight part of the "T" connector ( this is good because it means the circuit used to "excite" the alt is functional ) So does this mean my alt is bad even though it tested well and functional??? Quote Link to comment Share on other sites More sharing options...
ktm Posted May 9, 2009 Share Posted May 9, 2009 Probably.....and it means that your battery is already dead. Anything lower than approximately 12.5 volts and your battery is drained. Fuel pump flow is related to the input voltage. Low input voltage results in lower flow. Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 9, 2009 Author Share Posted May 9, 2009 Probably.....and it means that your battery is already dead. Anything lower than approximately 12.5 volts and your battery is drained. Fuel pump flow is related to the input voltage. Low input voltage results in lower flow. Well...yes...this is true and its why I suspected a voltage problem initially...but I need to know why my alternator tests well on a bench but refuses to excite in-car. The battery is fine ( albeit drains because the car's only running on the battery ), but isn't being fomented by the alt. Quote Link to comment Share on other sites More sharing options...
The570Z Posted May 9, 2009 Share Posted May 9, 2009 Have you checked your engine bock ground? And alternator case ground? Odd and roaming current spikes tend to be ground issues in my experience. Not sure if yours has a charge light, but if you do, check and see if its coming on when you turn the key on. If its not, check for resistance from the L terminal to the alt case, if its open, somebody is lying on the bench test . Quote Link to comment Share on other sites More sharing options...
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