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Thread: 90 SC power loss WOT

  1. #16
    Join Date
    Apr 2018
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    North Bay, Ontario
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    26
    I ended up sticking to a .052 gap and no change. However it finally threw a code at idle... code 66 MAF voltage below 0.4. So I'm going to order a new MAF. When car idles warm I register 0.54 after it bogs I pull over and measure 0.33. WOT on bog condition is 3.55.

    Also I know it's not a spark or ignition issue, plugs are golden brown so its stoich running perfect fuel, and when it goes this big condition, I leave the car in 2nd gear, shut it off, turn ignition back on and it'll pull hard again. So it's an electronic issue. I think now the MAF is my trigger after all.

  2. #17
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    Apr 2018
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    North Bay, Ontario
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    So... still having issues. What are the signs of a failing EEC? MAF voltage was showing low when condition encountered, swapped MAF and same thing good reading when warm, then drops reading from 4.8V WOT to 3.51V WOT. 2 MAFS same problem, only 1 is brand new. Same with TPS, readings good when cold, warms up and signal at WOT not coming up to voltage. Just replaced alternator as it died last week and battery also has a dead cell. I'm looking for ideas as to what is causing this voltage loss to the sensors after car is running. Like I said, when warmed up but driven for a few minutes things are fine, after that no power and refuses to go past 2800-3000 RPM at 3/4 to WOT. I'm losing my mind hoping it's not the EEC.

  3. #18
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    Dec 2007
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    Quote Originally Posted by Tunevo View Post
    Just replaced alternator as it died last week and battery also has a dead cell.

    Bit late, perhaps, but just a headzup - resist using the SC's alternator to recharge a dead battery...that's a quick way to quick alternator death. If the battery is dead, put it on a charger first.

  4. #19
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    Apr 2018
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    North Bay, Ontario
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    Quote Originally Posted by KMT View Post
    Bit late, perhaps, but just a headzup - resist using the SC's alternator to recharge a dead battery...that's a quick way to quick alternator death. If the battery is dead, put it on a charger first.
    Yes, as always. I trickle charged it last night, changed the alternator this morning. Would a bad cell battery cause electrical gremlins? I'm at a loss as to what's messing up my electronics signal. I had put 2 new 4GA grounds on the car, 1 to chassis, 1 to engine, so that should eliminate grounding issues. I can't figure this out for the life of me and no CEL issues or codes at all.

  5. #20
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    Quote Originally Posted by Tunevo View Post
    Would a bad cell battery cause electrical gremlins? .
    Not sure we've gone over it in this tread yet, but anything that results in less than, say at least 12.7 volts, will raise heck with an SC's nervous system.

    I'm at a loss as to what's messing up my electronics signal.
    EMI, for starters, typically from compromised/ad-hoc wiring harnesses.

    I had put 2 new 4GA grounds on the car, 1 to chassis, 1 to engine, so that should eliminate grounding issues.
    Depends.... In the example where the accy. bracket & engine/heads have been painted, you can add grounds all day long, but if the DIS doesn't see a proper spec ground back to the battery, all bets are off. Another is when the EEC has been out and the center bolt hasn't been re-installed...it's the ground there.

    Adding grounds is a good troubleshooting tactic, when used correctly, but there is nothing that will replace the factory ground paths. Confirm them whenever possible/replace if in any doubt...corrosion loves to hide out of sight. EVTM is your friend in that case, and the factory Engine/Emissions Diagnosis shop Manual is next.

  6. #21
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    Apr 2018
    Location
    North Bay, Ontario
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    Well, battery tests low CCA, confirms bad battery 75% health 12.4V charge engine off. ALT is putting out 14.3V at idle, 15.1 @ 2000rpm. Not sure what you mean by EMI? Factory unmolested harness, seems all intact, however about the grounds... does the factory small ground on the chassis in front of the battery have a link in it? So seems that my factory ground cable on the battery does no grounding at all. Hence the other grounding that I have put in place. I would like to get my hands on an EVTM or factory manual... however I have neither, only a Haynes manual, which has some useful info but not specific to supercoupe and doesn't help much.

    So now you mentioned grounds, I may just check into that factory battery ground... then check grounds to the EEC and signal to the DIS. Tach is working fine, but you got me onto something, this is good. I hope it's something simple. And new battery is in the mix tomorrow as well.
    Last edited by Tunevo; 09-04-2018 at 10:21 PM.

  7. #22
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    Quote Originally Posted by Tunevo View Post
    then check grounds to the EEC and signal to the DIS.
    In that case....see http://mnharms.com/tutorials/disnostart/

    EMI: see https://en.wikipedia.org/wiki/Electr...c_interference

    At least one of the wires in the front/upper harness leading from the crank sensor is wrapped in shielding/foil. When that protection is removed/compromised, signals to/from the EEC can go out of spec and cause various issues, from misfires to no-start.

    Donate that haynes to goodwill (it may be the one with the incorrect firing order, so...) and grab factory manuals. Google for sources, or try eBay.

  8. #23
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    Apr 2018
    Location
    North Bay, Ontario
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    So, grounds are all good, tested AMP draw from fuel pump while driving. Goes from 5.5A idle to 3.3A under load... which looks to me as if the fuel pump is not pushing like it should and may be on the way out. High Amperage would state a blockage in the filter as it's working too hard. Going to replace the fuel pump, and if that's not it, looks like an EEC issue that's causing a power drop across all sensors. See what happens when I get to it now I guess.

  9. #24
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    Quote Originally Posted by Tunevo View Post
    Goes from 5.5A idle to 3.3A under load... which looks to me as if the fuel pump is not pushing like it should and may be on the way out.
    Quoting off the 'net "Mechanical resistance inside the pump can result in higher-than-normal average pump current. A clogged fuel filter or fuel line restriction will also increase pump current. Electrical resistance, either in the pump or elsewhere in its circuit, lowers available pump voltage and reduces pump current."

    If in fact you did see 5.5a at idle and a reduced current of 3.3a under load (vs. 3.3a/idle & 5.5a/loaded), that would indicate high resistance in the circuit, which is not uncommon on these cars at the fuel pump connection/harness. If you do replace the pump (good idea regardless once you've dropped the tank), be sure to validate the wiring/connections, which might be the only real issue.

  10. #25
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    Apr 2018
    Location
    North Bay, Ontario
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    Yes I want to make sure good contact at and in the tank, however, the car ran great up until i changed the fuel filter... which is strange as it should have had better flow, and filter is the correct direction. I know grounds, power and everything at Bothl ends of the plug at the tank are good. My buddy told me should be around 5-7A as a good reading. Looking into a spare EEC just in case something there is going bad. Board looked good, traces good both sides. But the part that makes me think EEC is amperage drops at the FP at WOT, MAF voltage drops at WOT, TPS voltage drops aft WOT, losing everything after 5 mins driving under load at the same.points. It'll run at 60kmh in 5th at idle all.day long with no WOT issues, only when it's been seeing boost or load on the road. It's definitely a new issue I've never come across. All sensors are 100% just blowing me away on this one

  11. #26
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    Remind me...did you get a chance to check fuel pressure yet?

  12. #27
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    Apr 2018
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    North Bay, Ontario
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    No, just waiting to get pressure tester tomorrow, nobody has one here. Buddy going to lend me his.

  13. #28
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    Apr 2018
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    North Bay, Ontario
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    So fuel pressure test is done, 38 psi at idle, under load drops to 19-20psi at the rail while driving. Comes back to 40psi when I let off throttle. Shut car off for 2 seconds, restart and fuel stays at 40psi for about 30 seconds under load then drops to 20 again. No vac leaks. That's where its screwy, if the pump was 100% on the way out, why would I get pressure back after key off and restart and have good fuel supply again. And in the meantime, my MAF and TPS read low voltage at the same time and follow the exact same trend as the fuel pump. It's like a total system voltage drop across everything.

  14. #29
    Join Date
    Jul 2005
    Posts
    418
    Good evening


    Remove the fuel pressure regulator vacuum hose and record the fuel reading under load. https://www.youtube.com/watch?v=peh7-pFycyc


    Check fuel pressure volume. https://www.youtube.com/watch?v=rXS9jOTjut4

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