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Kimsen

Cant Rev over 4000 Rpm

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Kimsen

Ive got an 205 gti with an 8v Motronic 1.3 Ecu , the Car stood for about 10 years after some work the Car Finally Runs but i cant drive it yet it stays on Jackstands and needs some suspension works , but even in neutral i cant rev it above 4000 rpm... and i mean not a single turn over 4000 rpm  ... its like a Rev limiter , it sounds like misfires but when i go to 3900 rpm it sounds good, can you guys help me 

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jackherer
Posted (edited)

It's usually caused by the ignition amp, for some reason it is always 4000RPM.

 

BTW Welcome to the forum :)

Edited by jackherer

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Kimsen

Thx for the quick answer and hello there :) , i forgot to say something i changed the amp for another used one and its exactly the same thing , i also quick changed the Ecu but nothing worked ... so i hope i didnt get 2 busted amps so if thats the case that would be horrible , and another question the Amp isnt sitting in its orginal position. its mounted on the right Suspension Dom with a .. i think its an Aluminium Plate and it got the right holes in it to fit the Amp and on that plate are 2 ground cables that goes to the engine ground.. and it doesnt matter if the engine is hot or could it never goes over 4k

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jackherer

Have you got any thermal transfer paste between the amp and the aluminium plate?

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Kimsen

no i dont have 

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jackherer

That could be the problem then, you definitely need some.

 

You can use either automotive or electronics/computer thermal paste.

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jackherer

Also what brand are the amps? Anything other than the original Bosch part can be troublesome.

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Kimsen

Ok i will try that, and yes both of the amps are from bosch, my friend got an 16v maybe i can try his amp real quick tomorrow , do you know if its the same amps in the 16 as in the 8v?  Btw can you tell me what that termal paste does? i removed the original amp one for the first time but didnt see anything else as pure metal on the amp 

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jackherer

The XU9J4 Mi16 amp is the same as the 205 GTI one.

 

The paste conducts heat away from the amp into the aluminium heatsink plate.

 

https://en.wikipedia.org/wiki/Thermal_grease

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Kimsen

Ok i will get that tomorow and hope it will fix it , is it possible that the amp can overheat even when the engine is running for 10 seconds? Btw Thx for the fast answering you are really nice person , it helped me,  i will check all of that and hit you up with the news.

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jackherer

10 seconds is fast but I think it could be possible, they may even be permanently damaged if there was no paste at all.

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Kimsen

So i checked many things today , at first i bought some heatpaste and give it a try  but i got no luck with that , then my friend came over and said he found a brand new one in his garage so we changed it and still the same problem.

Checked the distributor cap and its fine , then i cheked the signal coming from the ecu to the amplifier and it looks good , 5v/20ms peaks look fine, then i installed my wideband 02 Sensor from my Racing engine and then i saw it run very very lean in Idle but it runs smooth, when i hit the throttle its still lean but it get to 14,2 afr by 3000 rpm so not that bad, when i go further to 4000rpm it begin to misfire/rpm limit and then i can see on every misfire it goes to lean then come back to normal in a split second, is it possible that the injectors cut out and then only Air goes trouh and it gets lean at the exhaust, because when it would cut the spark then the mixture would be rich because of the fuel that didnt burn. or im wrong? 

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jackherer

If it's going lean it might be worth checking the fuel pressure, the pump or the regulator might be failing. I wouldn't have expected that to cause a sudden cut off like a rev limiter as you described though.

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Kimsen

ah i forgot something, the check engine light comes on after reving it , how can i check witch code is saved and is there an safety mode in this ecu when engine light is on ?

 

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SRDT

I have this:

https://prepa205gti.files.wordpress.com/2014/01/bosch_motronic_m1_3.pdf

As usual it's in French.

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Telf

You can't check for codes the ECU is very basic and pre the code reading era.

 

Could the ECU be unserviceable? As in the rev limiter? Have you swapped it for a known good one?

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Anthony
2 hours ago, Telf said:

You can't check for codes the ECU is very basic and pre the code reading era.

 

This is a Motronic car which does have limited code reading capability - it displays codes via a flashing LED using the 2 pin diagnostic plug.

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Kimsen

How to read it? And ive checked the Fuel pressure its 3bar and in Idle 2,5 bar , itz driving me crazy where should i search nxt , the symptoms say when you have a rev limiter/ misfiring its the amplifier but ive checked it twice witch 4 different ones with heat paste. I dont now what to do next its frustrating

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Kimsen

And afr says its lean but sparks are black and a litlle wet 

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jackherer

If the engine management light is coming on then the next move has to be checking the error codes.

 

I'm pretty certain this ECU doesn't have any sort of limp (safety) mode though, I don't think it is intentionally restricting the RPM.

 

The diagnostic connector and the list of fault codes are in the document posted by SRDT above ^^^

 

You'll need to use a paperclip or a bit of wire on the diagnostic connector (M720) to make it flash the codes via the engine management light. I forget the details so you'll have to google motronic M1.3 fault codes if you have trouble doing that.

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Telf
8 hours ago, Anthony said:
10 hours ago, Telf said:

You can't check for codes the ECU is very basic and pre the code reading era.

 

This is a Motronic car which does have limited code reading capability - it displays codes via a flashing LED using the 2 pin diagnostic plug.

You live and learn- I didn't know that

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Kimsen

So got an Hour today for some checks, so basicly for me it really sounds like and issue with the Ignition system so i went for it. Checked Power and Ground from the Coil even cleand all Ground Cables and maked some new ones. Then i started up and nothing has changed    so i was not happy at all and played hard with my throttle and then something happend it did go over 4000rpm and it runs smooth when it does that then i went below and again the same problem so i went for another flattering throttle and after 10 seconds i get it again to 6000 rpm , then i shut it off and begin to think, components can do over 4000 rpm ok, wiring must be fine to ok, i swapped all parts and nothing changed ok, then i began to come back to the basic and Checked the input signal from the Ecu to the amplifier and then i saw little hikes around 4000 rpm , then went to the coil and Checked the signal from the amplifier and there it was big hikes sometimes even no signal at all... then i head directly to the ouput signal from the Ecu and the same its sending some hikes at around 4000 rpm .... then i needed to go and pick up my son .... so what to do nxt ? Check Rpm Sensor and Knock sensor?

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DamirGTI
Posted (edited)
11 hours ago, Kimsen said:

And afr says its lean but sparks are black and a litlle wet 

 

Both excessively lean and rich mixtures are notoriously hard to ignite .. puts a lot of strain on ignition system and misfires are common "by-product" ..

 

There's no knock sensor on 1.3 Motronic system (but me thinks it can be added to the ECU) , crankshaft sensor from my experience either works or doesn't and shouldn't cause that .

 

I'd have an look on the AFM , take the plastic cover off , unscrew and remove the surrounding plastic cover base too to give full view on the carbon track .. and inspect the carbon track , if its worn out or pitted , if so white areas or spots will be seen on the surface like so :

 

Good :

 

2754078010ae63c60303032263fcb6a22d105437

 

 

Bad :

 

2754078350f47f7f8c95ab6b15ef039eb0edc69b

 

 

.. notice - white worn out areas on the carbon track .

 

 

Also see if the AFM flap swings fully open and close without binding or sticking midway or similar ... had one with failed flap bearings (there's two small bearings on the flap shaft which centres the flap inside the AFM base) on which the flap canted off centre and started rubbing against the AFM body around mid way position .. blocking/resisting flap opening with the incoming air .

 

And another thing , inlet mounted square type coils on 1.3 Motronic system often fail .. much more often than old cylindrical coils on Jetronic 205's .

 

D

 

Edited by DamirGTI

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Kimsen

Thx i checked and it totally was worn out so i changed it with another and now its perfectly with the afr :) .. Thx alot ... But id did not not change my main problem , so far i changed Crankposition sensor ,Afm,Amplifier, Coil,Ecu,Fuel,Checked fuel pressure, maked some new Ground wires to the coil and amplifier and to the chassis and engine,Checked Crank position sensor cap , 02 Sensor changed  and still the exact same problem nothing changed and engine runs good even when it goes over 4000 rpm sometimes 

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DamirGTI

Do you still have cat. converter on this car ? not quite the usual symptom for blocked exhaust but who knows , if you have cat. and suspect it's blocked or the muffler restricting the exhaust flow try to rev it with the O2 sensor removed from the downpipe so it'll create hole for the exhaust gas to escape before cat. and muffler(s) .

 

Do you have EVAP system still on this car ? or it's been removed ? .. EVAP solenoid valve if removed/unplugged will set fault code , i remember mine (also 1.9 1.3 Motronic) used to turn on the engine check lamp while reving , but not "blocking" the revs on 4000 like yours , but i never investigated what is the issue as i do not use that car .

Anyways , if the EVAP system is removed , an 1.2Kohm resistor must be soldered on the solenoid 2pin plug to "mimic" solenoid presence on the system .

 

Tried reading the ECU fault codes as described above ?

 

 

D

 

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