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No power after braking Topic is solved

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Cammer
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No power after braking

Post by Cammer »

I have a 1996 GLE 2.4L with abs and tracs. It has 162,000 km. Since it’s a ‘96 it doesn’t have the self diag. trouble code unit. I bought an Autel MaxiDiag Elite. The meter will read brake codes and SRS codes but not engine codes. I made an LED probe unit to probe the OBD II socket (below the coin holder). The only flash code I could get was 512. I erased the code to see if it would return, but then got 1.1.1. The car starts fine and runs ok until I have to apply the brakes, it then loses power, won’t climb even small hills. If I give it more throttle, it has a small backfire. If I shut the car off and restart, the power returns until I again apply the brakes. I took it to the dealership, they said it needed a new cam position sensor. I bought and installed a CPS, no difference. I went through MVS, found a suggestion to replace the throttle position sensor, did that, again no difference. I can’t hear any vacuum leaks under the dash or around the brake vacuum booster. I haven’t opened the abs unit to resolder the feed wire connections, I’m guessing that could be next? Any suggestion would be greatly appreciated. (Sorry this is so long)
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theWIFES_S70
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Re: No power after braking

Post by theWIFES_S70 »

Cammer? Have you had your ABS unit rebuilt yet? Matty Moo does it on here for us. He'll ship you one and you'll have it in two days. Or you can ship your unit and wait a few more. All P80 ABS units fail. I think they soldered joints with cod liver oil instead of lead. My guess is once you get that ABS unit resoldered, your car will be as good as new! (At least until individual ABS wheel/speed sensors start to fail... Sigh...)
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Cammer
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Re: No power after braking

Post by Cammer »

Thank you for your input, Wife’s_S70!! I’ll arrange for a reconditioned ABS unit from Matty Moo tomorrow. I’ll let you know how I make out after the install. Cheers
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Re: No power after braking

Post by Fosgate »

How would ABS unit cause the engine to lose power? I would suspect you have a faulty one way valve on the vacuum line going to the booster... And/Or more likely leaking booster itself..
I would try blocking that line going to the booster, take car for a drive in a safe open area (as it going to be harder to stop the car without the vacuum assist), then try braking and see if the engine starts to play up again... This way you can eliminate anything related to brakes and vacuum leaks at the booster.
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Re: No power after braking

Post by Sommerfeldt »

Fosgate has a good point. It's hard to see how the ABS unit would cause the symptoms - a major vacuum leak would be far more likely, especially considering the backfire. There has to occur some kind of air/fuel mismatch for that to happen, and the brake booster is a MAJOR vacuum point (have you looked at that massive line? :D ).

I for one would second Fosgate's procedure. Do find a safe place to do it though - if you've never driven a car w/o brake assist, it's hard to know the kind of effort you have to put into getting that amount of steel to stop rolling.

- S
'96 855 T5, R bumper and spoiler, Koni Yellows & blue H&R springs all 'round.
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Re: No power after braking

Post by erikv11 »

Brake booster itself, or the vacuum line that leads to it, are at the top of the list. ABS unit is not on the list.

I'd start by replacing the booster vacuum line, before the trickier and good suggestion from Fosgate.
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Re: No power after braking

Post by Clemens »

You would have the ABS and TRACS light on if the 96 and up ABS module fails. And it won´t cause a loss of power.
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Cammer
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Re: No power after braking

Post by Cammer »

Thanks again to all those who have responded. I pinched the brake vacuum hose in two places, just to insure that it was pinched completely shut. The pedal braking force needed assured me it was inactive. Went around the block (with assist of the parking brake). Had to pull over and restart the car four times, due to lack of power. After restart it was ok for another 100 yds. Sometimes there would be a minor backfire before pulling over to restart. After the restart the engine would run fine, then lose power and wouldn’t go up the smallest hill. Still no OBD codes or dash warning lights. I’m pretty sure the idle air control valve doesn’t run even at idle (not sure how this could have an impact on the problem?)
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Re: No power after braking

Post by Sommerfeldt »

Loss of power and the backfire still sounds like a massive vacuum leak/boost leak somewhere. It sounds like what happens when a hose comes completely off and just hangs around approximately where it should be, until you poke at the throttle.

- Check all your air hoses. Remember that if you have the black rubber hoses, leaks can be hard to detect. Use starter gas if needed, but I personally don't like it. Take the hoses off, use a flashlight, squeeze the hose to reveal any rips/tears/holes.
- Check your MAF. Your 512 code indicates it may be super cranky. Disconnect it and let the engine run off base tables. See if the car runs better - you'll see some loss of power and maybe some black smoke if you load the engine, but it should be driveable. You'll get a CEL, but never mind that - it'll clear on its own, or you can clear it yourself.
- Check all your vacuum hoses - ideally, you should replace them with silicone hoses anyway, if they haven't been replaced since new.

Check that your TRACS/ABS light(s) are functioning. If there is indeed something wrong with your ABS unit it/they should be on. It's still hard to see where this could cause your symptoms, however.

Have you done anything to your crankcase ventilation? If so, check intake seal as well - it's easy to mess up and cause leaks during reinstall.

- S

P.S. Note that while the 512 probably is the short term fuel trim, that will reset each time you shut the car off, which may also be why the car probably runs off base tables at the start, and then gets f-ed up info from the MAF after a while, messing your day up.
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Re: No power after braking

Post by abscate »

I had a massive split in a vacuum hose which gave me a horrible cold start and run condition, but once the car went closed loop it ran very well. I’m talking a hose which had a 5 cm long piece missing...

Checking vacuum hoses means removing them and replacing, and you may as well refresh them since you’ve done all the Labour looking at them

Looking with your eyes wastes everyones time , as does reporting “ they look ok”
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