Hi, I have audi a4 1.8t quattro 1995 (aeb), and having hesitation at wot between 3000 and 4000 rmp, in other range car accelerates good.

I have boost gauge and boost goes to 9 psi by 3000 rpm and when hesitation starts it drops by only 1-3psi and at around 4000 rpm it boosts back to 9 psi and accelerates stong again.
And sometimes it goes to something like LIMP mode, and limits boost to 4 psi and I have to disconnect battery. But very rarely.

I read a lot about maf, and everyone suggested to disconnect maf and drive and car will go better if maf was the problem. I did that and car boost only to 4psi and holds that through whole rpm range.

So is the maf causing the problem or something else? Why it limits the boost to 4psi without MAF?

 

You could try something as simple as buying MAF cleaner from the autoparts store, and clean your MAF with it. If that makes a difference then it may be time to get a new one.

Also, scanning the ECU for stored codes (is your check engine light on?) may be useful to give you a potentially better idea of what the issue is. For example, it could be a misfire.

 

Thanks, I`ll try cleaning MAF first. I had some code last time my friend scanned(while ago), but it didn`t return code for few hours driving, it was something about mixture.

Check engine light is not on, even when I disconnect maf.

Could it be spark plugs too, causing this loss of boost and power in this specific rpm range?

I`ll scan again and let you know if there is code again...

 

update

I tried disconnecting maf again, while car was running and idle changed for a second when I unplugged it, so I guess maf is working.

Can`t compare under WOT cause without maf boost is limited at 4 psi, and it runs normal but slow, no hesitation.

I noticed constant hissing while accelerating under full boost(similar to dv), somewhere very close to me, left side of the car, where the intake manifold is. Could it be leak causing this kind of problem?

 

It's certainly a possibility, but I wouldn't think a leak would cause the harsh behavior you described, unless it were a really bad leak. IF it were a very bad leak you might not even be hitting 9psi. In any case a boost leak tester could really come in handy since leaks are often inevitable as these cars get older.

 

I was thinking the same, why it holds boost till 3000 rpm than drops if it is a leak. Not sure. But how do you mean harsh behavior? Boost drops to 6-7psi at 3000 rpm and moves a little bit up down..(so "only" 2-3ps loss), than fine at around 4000 rpm again

Also this loss of boost/power is most noticeable in lower gears, in first at wot is the worst.

I`ll check all in few days, hate when car is not going like it should...

 

Ah my mistake, for whatever reason I was thinking you were dropping to 2-3psi instead of a 2-3psi drop.

 

update

I`ve checked all lines and it seems there is no leak. Also DV is good. Now, every day car seems to run better and better, almost no boost loss at 3000 rpm, sometimes just 1psi down so it holds 9-10psi. Who knows what was the problem.

I`ll buy a chip in a few days and see how it will go.

 

Do you know how old your N75 valve is? This is kinda an off-the-wall thought, but since the N75 effectively controls the boost level (through the wastegate actuator) it could be/have been the culprit.

With the current setup I have if I close my manual boost controller (MBC) all the way (my MBC and N75 are in parallel) then in 2nd gear I get a boost spike well past 25psi, but the boost settles at 19-20psi. This spike doesn't really occur in any gear besides 2nd. And this spike is simply due to the massive build-up of boost pressure starting at low RPMs. The MBC right now is set at 19-20psi to eliminate the spike.

So what I'm thinking - you might be getting a boost spike from a partially malfunctioning N75 valve.

Also, stock 1.8T engines with AEB engine code should only be hitting 7-8psi at full boost. I'm curious what difference the chip will make.

 

I`ve change n75, it is a new one. I have first tried n75j but had throttle cut with stock ecu so I changed to new stock F version.

That`s strange, mine`s 1995 AEB It is pulling pretty strong, but chipped will be even better with 15psi at least. Maybe 1995 has different ecu, 9-10psi should be little more than 150HP than.

I`m not getting any spikes at wot, it goes pretty soon to 9-10psi and stays there, never above 10.

I had most noticeable problems in first gear, it couldn`t reach max boost at wot, only after 4500 rpm, which is very late. Now it makes it at 3000 rpm. Hope it will last.

I was thinking to get MBC but my injectors are pretty small(210cc) so don`t want to run lean.

You got nice setup, I was wondering how your car pulls, guess you have problems with wheel spin . Right now, mine does 0-100mph in 19s, not so good ... I`ll see the difference after chip, maybe 2-3 seconds of that time.