B5 A4 1.8t AEB hitting a rev limit at 5000 rpm?

[TheB5guy]

Hey everyone, im new to the forum but have searched through it to see if i could find an answer to my problem. So far it seams like a maf or cat problem but i unplugged the maf and it idles the same and still hits the "rev limit" only difference is it will only boost to 5psi at wot. It cant be a clogged cat because it doesn't have a cat so im not sure what it could be. Pulled dtcs and had a code for the cat and a p1136 (long term fuel trim add. fuel b1 system to lean) so i researched that, bad maf, o2 sensor or vac leak. Boost gauge says 20 vac at idle, 23 vac on decel and will hold 13 psi wot (t.a.p stage 1 ecu). No misfire codes or any other codes. Any idea what it could be? Any and all responses are appreciated!

[Bordom]

Hey everyone, im new to the forum but have searched through it to see if i could find an answer to my problem. So far it seams like a maf or cat problem but i unplugged the maf and it idles the same and still hits the "rev limit" only difference is it will only boost to 5psi at wot. It cant be a clogged cat because it doesn't have a cat so im not sure what it could be. Pulled dtcs and had a code for the cat and a p1136 (long term fuel trim add. fuel b1 system to lean) so i researched that, bad maf, o2 sensor or vac leak. Boost gauge says 20 vac at idle, 23 vac on decel and will hold 13 psi wot (t.a.p stage 1 ecu). No misfire codes or any other codes. Any idea what it could be? Any and all responses are appreciated!

Sounds like limp mode. Strange a stage 1 tune will only boost that much

[TheB5guy]

I thought it might be limp mode but from what ive read on other posts it seams like limp mode wont even let you rev that far but im not sure. How do i get it out of limp mode and how to i keep it out of limp mode? Thank you for the quick response!

[ytrezzzz]

There is no limp mode on AEB because there is no boost controler on this engine

[rjpiselli]

N75 a possibility. In place to make sure you don't over boost. Can you go above 5k rpm if you are extremely light on the throttle? Misfire codes could just be a side effect of the n75 working.

[ytrezzzz]

Maybe a faulty knock sensor ? i had this problem on my car

[TheB5guy]

N75 a possibility. In place to make sure you don't over boost. Can you go above 5k rpm if you are extremely light on the throttle? Misfire codes could just be a side effect of the n75 working.

I've only tried wot and like 3/4 throttle, so if i can get past 5k with little throttle then check or replace the n75? I didn't get any misfire codes btw.

[BaseDrifter]

You said you unplugged the MAF and the car ran the same? It didn't get worse? That could be your problem right there. The code you pulled also points to a b

There is no limp mode on AEB because there is no boost controler on this engine

There most certainly is. There is no MAP sensor, but there is a boost controller (N75) and limp mode even on the earliest 1.8Ts. Lord knows I've been stuck in 5psi limp mode more times than I care to remember. One of those times was due to an improperly installed shim in a forge 007 that blocked the vac/boost reference line.

[S4NIK8]

I've also seen limp mode on my AEB car and a couple other AEB's. Yes it is a thing on AEB cars and yes it will limit you to wastegate pressure.

[TheB5guy]

I unplugged the maf, idle was the same, still hit the "rev limit" but only boosted to 5 psi. I then plugged the maf back in, did a little drive, still hit the 5k rev limit but would hit 13psi.
Will resetting a chipped ecu do anything to it like mess up the tune?

[pbcrazy]

May be unrelated, but I had a T.A.P. tune for a little bit and I cannot tell you how many problems it had. Just a bad tune all around, as soon as I got a different one most of my problems went away, though I did not have this specific problem.

[GrapeBandit]

I had the same issue on my aeb. bad n75 caused this. I deleted the n75 and run stand alone MBC

[rjpiselli]

I've only tried wot and like 3/4 throttle, so if i can get past 5k with little throttle then check or replace the n75? I didn't get any misfire codes btw.

Yes, the would be where I would start. When the n75 was bad on my car, I couldn't go wot or even close, however I could still hit high rpms. It's bc the n75 cuts boost, not invoke a rev limit. And it just likely takes until 5k for you to build "too much" boost. See if you can hit higher rpm with less throttle.

[TheB5guy]

Thank you everyone for the responses! Ill try a low throttle run tomorrow and and let you all know how it goes.

[TheB5guy]

Well no luck with the low throttle/low boost, still hits the 5k limiter. Should I still replace the n75? I was looking at the one on uro tuning. Also my DV is stock, upgrade to 007?

[TheB5guy]

Well did a ecu reset, same problem. N75 is ordered and on its way. Could it have to do with timing or cam position sensor? Or maybe just a bad tune?

[rjpiselli]

Well did a ecu reset, same problem. N75 is ordered and on its way. Could it have to do with timing or cam position sensor? Or maybe just a bad tune?

Hmmm I don't think its your n75 at this point. Does it hit a 5k rev limit in neutral? The n75 is pretty much a boost related issue. if you cant reach beyond 5k rpm even when your not building high boost I would say nay on the n75. If you can return it, I'd hesitate on the install of that.

I am not familiar enough with all possible effects of a cam position sensor to recommend replacing that; but I can tell you on my sisters cabriolet, it cause the vehicle to all but die once it reached operating temp. When the temp cooled, the car would fire up and run like a champ; but as soon as it reached operating temp it would just quit and wouldn't start. Replaced cam position sens and ran like a champ ever since.

Not saying your issue cant be a cam position sensor, just telling you what my experience with that was. again though, i do not think that its your n75 if you are not able to go past 5k even when your babying the car or in neutral, because the n75 releases boost pressure and under those conditions you wouldn't build up enough for it to become an issue.

[S4NIK8]

Have you tried a new MAF?

[TheB5guy]

Yeah it drives fine at operating temp and it boost good and pulls good just cant get past 5k. Could a bad maf induce a lower rev limit? I'm going to search the forums about maf issues and see what others say.

[crazy tarzan]

Change fuel filter? Possibly fuel pump issue? Clogged injector? I'm on a UTV race team, we had a motor that would run, sound good, but the UTV wouldn't go over 30 mph (we get up to 80+ mph normally). Turned out to be a clogged injector on one cylinder. It would limit how far the motor could rev. . .

[TheB5guy]

Would it just rev to a certain rpm and just stop? Mine bounces like a regular rev limit.

[crazy tarzan]

Not sure, I wasn't in the car at the time it was running (it was examined/troubleshot also while I was not present). I can find out?

[TheB5guy]

I read on another fourm that being one tooth off on the timing belt can cause it but I would imagine it would cause a lot more problems other than a lowered rev limit

[S4NIK8]

Where in minnesota are you?

[Radskull1]

does it feel like the turbo shuts off at 5k rpm?

[TheB5guy]

Yeah Burnsville area, and no its 13-14 psi all the way, pulls good too

[BaseDrifter]

Can you make a video of the problem? You can't get past 5k in any gear?

Maybe it's a throttle body or throttle cable problem.

[S4NIK8]

Yeah Burnsville area, and no its 13-14 psi all the way, pulls good too

Have you just used a generic obd2 scanner or a vagcom to scan this?

[chris164935]

Could be your crank position sensor starting to fail. I had an issue with my car where it felt like I was hitting a rev limiter. The car would break up and stop accelerating in higher RPMs. Replaced the crank position sensor and the problem went away. If you have a spare one or one you can borrow from someone, wouldn't be hard to change it out.

[TheB5guy]

Yeah use a generic obd2 and had a 02 sensor code (can't remember what it was, its catless) and a p1136 that was the only codes. Thought about the crank sensor, any good place to order one for a good price/quality?

[S4NIK8]

I would test for boost leaks and try a different known good maf before replacing the crank sensor.

[Bordom]

Have you adjusted the throttle cable? Are you 100% certain the throttle opens all the way when the accelerator is depressed?

[TheB5guy]

I'm sure if the throttle wasn't opening all the way it would just stop at 5k but it bounces like a regular rev limit would. Ill try a good maf and see what happens other wise I think ill bring it to a shop

[TheB5guy]

Well haven't had much time to look into my problem but I also forgot to mention that the car idles at exactly 500 rpm. Could this have and correlation to the lowered rev limit?

[S4NIK8]

Have you replaced the cluster at some point in this car? A cluster coded for the v6 will show an idle of about 400rpm when inserted into a 1.8t car.