MG1->MG2 Problem? Huge Mileage Drop, Terrible SOC w new HVB

Discussion in 'Gen 2 Prius Technical Discussion' started by John Frank, Jan 20, 2017.

  1. John Frank

    John Frank New Member

    Jan 20, 2017
    2006 Prius
    Hi. First, I put this in technical b/c I think that's appropriate. Second, I'm trying to be concise to respect your time. It's already long enough. But I ran a lot of tests and need to communicate details.

    The Car: 2006 Prius, single owner, all maintenance by self, full synthetic oil always. Currently 218,000 miles.
    The Event: Overnight, loud ticking from engine. The mileage on 90 mile commute dropped from 44mpg to 28mpg at the same time. HV Battery (8 months old) never tops 56% SOC, and drops to 29.5% during highway portions. Suspect this lack of assist is responsible for mpg drop.
    What It's Not: Tire pressure, gas, plugs, coils, injectors, HV battery, 12V battery.
    How I Know What It's Not: Replaced plugs & coils. Torque app on OBDII shows 12V is good, all cells are good. 2 Bottles of Chevron Techron through fuel system for injectors.

    Now the "story": Hybrid Battery died last August. New one installed at dealer. No other issues ever. Did all my own work and religious about quality. Muffler pipe rusted through, so day before inspection on 12/18/2016 put in new muffler from the flange back. Changed brake pads and rotors on front. Changed plugs and did it all correctly (so please don't ask about getting something down the hole, proper torque, etc). Dropped car at local shop, passed inspection & emission (no check engine light). Next morning, filled up w gas, added fuel injector cleaner to tank. Coincidence or not, about 20 miles later the engine started making a loud ticking sound, only when gas engine is on (not when coasting, hyperglide, etc). Did not affect performance. By mid tank, mpg was terrible. Battery level suddenly seemed to always be at bottom or 2 bars. Added oil (it burns a bit, see below). In the few weeks since, pulled the plugs back out - no fouling, no piston hitting plug, etc. Replaced coils for good measure. No change in ticking sound. HV Battery charging remains woeful. Noticed that the "bars" on battery went up what seems normal when coasting and regen in effect.

    Got a Bluetooth ODBII tool and Torque app. Monitored the batteries and nearly every other sensor on the car. Everything looks good. Vapor Pressure, temps, all of it. Absolutely no check engine codes. So I put all the battery monitors on the same screen and drove several days. Here is my trip and what I note: 46 miles each way. First 12 miles on flat local 45mph roads with very few stops. Everything else 65-75mph on highway. SOC will be about 47% on start in morning. Because it's winter, engine runs and the flat road means a little power (5-8 kW) is shown as charging HVB. SOC is then about 54% when I hit the highway on-ramp. Over the highway miles, it drops down past 40% SOC (single bar on MFD) and continues down to the 30% point (as shown on Torque). On the MFD it's been 1 bar this whole time, and still showing like it's trying to give power to the engine. But at 30% it appears the design is such that it prevents the battery from supplying any power for safety. I'm basically running on a little engine at that point, but it maintains speed on the highway. When I coast the (MG2 I think) will charge the battery about 19-25 kW per Torque. But I coast very little maintaining 65mph. When I hit the off ramp, I can apply a light break. That kicks in regen more fully as I understand it. Torque shows charging at 55 kW, and a little more pressure on the pedal makes it about 95 kW. So coasting down a 0.4 mile ramp gives SOC rise ~9% up to 39%. On the 1 mile into work, a light accelerator keeps the engine running and a 5-8 kW flow to the battery, so I park w SOC about 42% and do it again on the way home. Believe it or not, I still manage to get 28-30 mpg with this situation. 1000+ miles this way now.

    Is the ticking related? I'm not sure. I went through all the techron, plugs, coils thinking something was bad, shorting, etc. Here's what I noticed about the ticking. It occurs about 1/4th of the engine rpm. If rpm shows 1200, you can literally count out about 6 ticks per second. So I think it might be that the oil got a little low once (I need a quart every 2 weeks = 1000miles) and maybe it sucked up some crap from the pan and a follower is now stuck and getting smacked by the camshaft every rotation. And while that may be the case, I don't see how that would impact the battery recharge tis badly. I'm also not sure how a stuck follower wouldn't result in a check engine code on a cylinder. Regardless, when I need another quart of oil I'm going to put some ATF in it and hope it's cleaning agents unstick the follower (if that is the problem there).

    I think from the HVB issue it's much more likely when the mechanic pulled the wheels to check the pads they might have damaged something that transmits the electric power between MG1 and MG2. But I'm not sure any wires are actually exposed. Since it puts out 95kW on regen, it's not bad stators on MG2, right? Oh, and it's not a dragging brake pad either - when I get to destination, I can touch the rotors with no problem. No excessive heat of any kind.

    So folks, I'm really stumped. In reading the stickies on how it works, I know MG1 should be sending current to MG2 to have excess sent to the HV Battery. Clearly that part is not happening on highway like it used to. Even when the MFD charge arrow is pointing that way at highway speed, Torque shows only a 5kW flow. Is that normal? Should it be higher?

    Are there codes I can track or graph with Torque that would help? I will capture and upload them if so. Any suggestions would be greatly appreciated. Took it to the dealer and they wouldn't look at it. They heard the ticking noise and said "you need a new engine". With no basis, no tests etc. So I've driven it 1000 miles since then with no problems other than the battery charging. Thanks in advance for your help.
  2. strawbrad


    Aug 9, 2011
    2005 Prius
    Hi John,

    Great first post. It's refreshing to see someone that's done their homework. A WAG would be the inverter or inverter coolant pump. But I would think you already checked that. You would think an overheated inverter would be throwing codes.

    It might be time to do a compression check on the engine. At least you could rule that out. A bad O2 sensor can really hit your mileage. Have you cleaned the MAF sensor and throttle body?

    You might have to wait for the problem to get worse so it will cause a code.

  3. edthefox5

    edthefox5 Senior Member

    Jul 25, 2007
    Clearwater, Florida
    2007 Prius
    well when hybrid battery stops participating it puts a huge load on the motor.
    The motor then reveals its age or condition.
    Based on how many posts I have seen about this issue and the fact it eats so much oil my arm chair suspicion is the motor is toast. I suspect somewhere along the line the motor was run very very low on oil and damage may have resulted or it spends its life chronically low on oil and
    Damaged over time. One very low oil event will usually do it. Especially if it lit the yellow check engine light. That's o oil pressure.

    We see this a lot now with engines that eat oil. Requires constant vigilance.

    The engine is splash lubricated and the oil should always be at the full line.
    Put the car in inspection mode so it runs continuously and get under front of car and listen for bad bearing noises.

    I suspect it wii throw a misfire soon or you will start to hear knocking under load and car may go into limp mode as the knock sensor pulls timing