No power at WOT

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Dmckim
Posts: 107
Joined: Thu May 22, 2014 12:54 pm
Location: Buffalo

No power at WOT

Post by Dmckim »

1980 633csi with L-Jet system. Motor rebuilt about 5K ago. Ever since I got it back, the car will lose all power when at wide open throttle. It doesn't matter what gear I am in. Once I back off the throttle, normal operations continue. I cannot replicate this parked in the garage manually operating the throttle - car red lines before the high idle switch is engaged. I assume because it has no load on it.

I checked both throttle position switches for resistance, and both seem to be working. I adjusted the TPS plate with no improvement.

The wires to the switch are both the same color (white), so I am hesitant to throw my meter on them to see if they are getting a signal from the ECU (don't want to fry it). This is the earlier design with two separate switches; not the later in the Bosch housing.

Car has some cold idle issues which I don't think are related as I had this throttle issue when it was idling fine.

Cheers,

Dale
1980 633CSi
1987 325is (sold)
2001 740iL Sport (sold)
2007 328xiT (Sold)
2014 320dT (Sold)
Current: 2023 Jetta GLI M/T
2007 GMC Sierra,
1972 Pontiac LeMans Sport Convertible
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sharkfan
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Re: No power at WOT

Post by sharkfan »

Fuel issue? Have you checked the pressure? Have you cleaned/checked the filter/s including the one in the tank?
2001 Alpina B10 V8 Touring (1 of 12 rhd)
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1982 BMW 635CSiA (1 of 100's left from the 1000's made and still valiantly fighting against a rusty grave)
Dmckim
Posts: 107
Joined: Thu May 22, 2014 12:54 pm
Location: Buffalo

Re: No power at WOT

Post by Dmckim »

Have not done recently...and looking at my records, probably 10 years ago. Might be a good place to start; and probably need to do regardless.

Cheers,

Dale
1980 633CSi
1987 325is (sold)
2001 740iL Sport (sold)
2007 328xiT (Sold)
2014 320dT (Sold)
Current: 2023 Jetta GLI M/T
2007 GMC Sierra,
1972 Pontiac LeMans Sport Convertible
GRNSHRK
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Re: No power at WOT

Post by GRNSHRK »

Hey Dale, you mentioned that both TPS's appear to be working because they have resistance, do you mean that when you set your meter to the resistance setting and open or close the WOT switch, the resistance goes from zero to infinity :-k

If yes, then it may be ECU related :roll:

I've actually got a Bosch L-jet manual, at home, naturally #-o

I'm gonna be off till mid next week but I'll try and take a look in the manual and get back on, which I tend not to do when I'm not at work, hate getting on a computer if I don't have to [-X

Hope all's well otherwise in Buffalo :lol:

:mrgreen:
:mrgreen:
Bobbo
1980 633 CSi Cypress Green/Pearl Beige
2017 X5 M Sport Xdrive 35i Carbon Black/Ivory White
2005 330 Ci ZHP Cabrio Imola Red/Bone/Black
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Dmckim
Posts: 107
Joined: Thu May 22, 2014 12:54 pm
Location: Buffalo

Re: No power at WOT

Post by Dmckim »

Bobbo

You have my multi-meter test down correct on the switches.

ETM says that the TPS feeds pins 3 for WOT, 18 for constant and 2 for idle in the ECU. I was going to test them to see if they were getting a signal with the ignition on, but couldn't tell what wire was what - they are all white. I didn't want to fry the ECU.

That being said, I think I might have a spare ECU to try at some point.

Dale
1980 633CSi
1987 325is (sold)
2001 740iL Sport (sold)
2007 328xiT (Sold)
2014 320dT (Sold)
Current: 2023 Jetta GLI M/T
2007 GMC Sierra,
1972 Pontiac LeMans Sport Convertible
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Brucey
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Re: No power at WOT

Post by Brucey »

the way these cars work at WOT is that the AFM reading is ignored and the ECU just throws fuel into the engine using a simple protocol. The injector duration (per engine revolution) at WOT will vary with temperature but not much else. IIRC even on closed loop systems, when the WOT setting is engaged, the same kind of thing happens (i.e. the O2 sensor closed loop isn't used).

On open loop cars the usual result of the WOT protocol is that the engine runs somewhat rich. The setting is chosen so that the mixture ought never be lean. If the airflow into the engine isn't high enough the result is usually that the WOT mixture gets even richer. A little mixture richness isn't a bad thing; more power and lower combustion temperatures (that won't burn valves so easily) ought to result. However in extremis, mixture richness can result in less power when the WOT setting is engaged, which is what I suspect you are seeing here.

Now it is possible that you might be getting a lean mixture at WOT but tbh I think it unlikely. In any event you ought to be able to see how rich the mixture is using a wideband lambda probe. You can try using the standard O2 sensor output instead but it won't show you much; IIRC the usual sawtooth signal under closed loop is replaced by a straight line; it'll tell you if it is rich or lean but not much past that.

As to what might be causing the issue, the usual suspects are the FPR, the CTS and the ATS. Any can fail in such a way as to make the open loop running very rich. Of these the CTS is favourite; check the readings at the ECU end of the harness (BTW some US spec 633s were fitted with an inline resistor near the CTS itself; this commonly fails and sends the CTS reading open circuit even if the CTS itself is OK) . An open circuit CTS will not prevent the car from starting and running normally from cold and if the closed loop running kicks in quickly enough that will compensate for the error in target value during normal running. However if forced to run open loop at all, the mixture will be hopelessly wrong.

So my advice is to check the input values from the sensors that control open loop running, and to check that the FPR is working correctly.

hth

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GRNSHRK
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Re: No power at WOT

Post by GRNSHRK »

Dale, FINALLY copied a couple of pages out of my L-jet workshop manual #-o

One is a troubleshooting flow chart for issues at WOT or not being about to reach top speed :-k

The other describes how to test the TPS switches on the Throttle Body =D>

HTH, lemme know if you want me to copy the entire manual, which I can, but it's already a poor copy of a copy :-({|=
Attachments
TPS test.pdf
(15.31 KiB) Downloaded 216 times
WOT troubleshooting.pdf
(21.27 KiB) Downloaded 222 times
:mrgreen:
Bobbo
1980 633 CSi Cypress Green/Pearl Beige
2017 X5 M Sport Xdrive 35i Carbon Black/Ivory White
2005 330 Ci ZHP Cabrio Imola Red/Bone/Black
Image
Dmckim
Posts: 107
Joined: Thu May 22, 2014 12:54 pm
Location: Buffalo

Re: No power at WOT

Post by Dmckim »

I love the flow chart! Thanks Bobbo. I will keep you apprised of the progress (or lack thereof)... :oops:
1980 633CSi
1987 325is (sold)
2001 740iL Sport (sold)
2007 328xiT (Sold)
2014 320dT (Sold)
Current: 2023 Jetta GLI M/T
2007 GMC Sierra,
1972 Pontiac LeMans Sport Convertible
Dmckim
Posts: 107
Joined: Thu May 22, 2014 12:54 pm
Location: Buffalo

Re: No power at WOT

Post by Dmckim »

Brucey wrote:the way these cars work at WOT is that the AFM reading is ignored and the ECU just throws fuel into the engine using a simple protocol. The injector duration (per engine revolution) at WOT will vary with temperature but not much else. IIRC even on closed loop systems, when the WOT setting is engaged, the same kind of thing happens (i.e. the O2 sensor closed loop isn't used).

On open loop cars the usual result of the WOT protocol is that the engine runs somewhat rich. The setting is chosen so that the mixture ought never be lean. If the airflow into the engine isn't high enough the result is usually that the WOT mixture gets even richer. A little mixture richness isn't a bad thing; more power and lower combustion temperatures (that won't burn valves so easily) ought to result. However in extremis, mixture richness can result in less power when the WOT setting is engaged, which is what I suspect you are seeing here.

Now it is possible that you might be getting a lean mixture at WOT but tbh I think it unlikely. In any event you ought to be able to see how rich the mixture is using a wideband lambda probe. You can try using the standard O2 sensor output instead but it won't show you much; IIRC the usual sawtooth signal under closed loop is replaced by a straight line; it'll tell you if it is rich or lean but not much past that.

As to what might be causing the issue, the usual suspects are the FPR, the CTS and the ATS. Any can fail in such a way as to make the open loop running very rich. Of these the CTS is favourite; check the readings at the ECU end of the harness (BTW some US spec 633s were fitted with an inline resistor near the CTS itself; this commonly fails and sends the CTS reading open circuit even if the CTS itself is OK) . An open circuit CTS will not prevent the car from starting and running normally from cold and if the closed loop running kicks in quickly enough that will compensate for the error in target value during normal running. However if forced to run open loop at all, the mixture will be hopelessly wrong.

So my advice is to check the input values from the sensors that control open loop running, and to check that the FPR is working correctly.

hth

cheers
Thanks for this too, Brucey. I think this might be part of it as well as I had a hard drive home with it yesterday. Kept searching for idle, then would settle, then back again. Seems like a sensor sending bad data to the ECU could be the culprit. I am chasing a lot of demons here, so trying to be deliberate. I am relatively sure I don't have any vacuum or air issues...famous last words.

Dale
1980 633CSi
1987 325is (sold)
2001 740iL Sport (sold)
2007 328xiT (Sold)
2014 320dT (Sold)
Current: 2023 Jetta GLI M/T
2007 GMC Sierra,
1972 Pontiac LeMans Sport Convertible
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