View Full Version : Possible ECU problem?

07-21-2018, 10:02 AM
Hello, my name is Woody. I live near Colorado Springs. Just joined the forum. I have a A4 that has been giving me a lot of trouble, hoping someone could offer some advice.

The car is a 1997 A4. It has a fair amount of modifications, such as: bigger turbo, forged rods, bigger deka injectors, E85 etc. The previous owner had most of the work done at Bluewater Performance and Berg Performance up in Denver. Bluewater did a United Motorsports 4E tune. It was super fun when it was running and I'd love to start driving it again.
The car has never been completely right but when I first purchased it a little under a year ago it ran fairly well. On a cold start, it would run very poorly and die unless I held my foot on the gas pedal for at least a minute or two. I know E85 can be finicky on cold starts but this was a lot worse than normal. The car was fine after it has warmed up. I assumed that was some sort of tuning issue.
When the car was doing this I could feel the throttle body kind of "pulling" on the gas pedal. I bought a new oem throttle body just in-case the whole throttle body was bad. I went to align the throttle body but VCDS will not communicate with the engine. It will do other systems but not "01." I've checked the voltage on the K line, cleaned the contact points on the gauge cluster, unplugged the aftermarket stereo, etc.
The car is even worse now. It doesn't want to idle for more than a second or two. The E85 has been sitting in the tank for awhile which doesn't help but I feel that this has to be somewhat related to the throttle body alignment. If I unplug the throttle body, it'll at least hold a steady idle.
Any suggestions? I was thinking of buying some sort of mail order tune just to see if it improves anything. I saw a dude in Michigan advertising his business, "Boost Dynamic Tuning." His prices seem fair and it's easier than having to tow the car up to Bluewater performance which is about 80 miles from me.

07-21-2018, 11:32 AM

Im by no means a tuning pro, or pro mechanic for that matter. I am an mechanical engineer and hobby mechanic on the other hand. So take my thoughts for what it is. Thoughts/ideas.

To me it sounds like fueling and or timing witch leads me to thinkin of the tuning in general. Im assuming you dont have e85 tune? What kind of ecu/tune is in it? It COULD be so that its no fault just a "noobish" tune making certain functions of the oe tune/ecu unavailable, if its a known tuning brand send them an email askin about the throttle body alignment. Someone with more experience could fill in, or you could google about finding more info on this matter.

I had some talks with a guy I was buyin parts to a e85 k04 setup im thinkin of going for. Ill go for petrol firstly though.

He had it runing good with the setup witch is for bosch 465 injectors, vr6 maf, k04 and some support mods.
What he said was that it sometimes had trouble startin specially when cold outside, on the other hand he lived in northern sweden with temps reaching -30 degress celsius....
But other than that it ran great, to good.. he destroyed the rods..

But he was runing a petrol tune with e85 and his solution was instaling an AFR sensor and adjustable fuelpressure regulator + bosch 044 fuel pump.
By doin this you can atleast get decent Air/fuel mixture witch will go a long way.

This might not sort all the problem but it could make it run atleast better. You could install afr/adjustable fpr and buy a spare ecu on a junkyard and see if you can align the throttle body with that..

Just thoughts and ideas mate...

Best regards Bleuw - Sweden

07-21-2018, 07:07 PM

I appreciate the response. The car has a United Motorsports tune. They're fairly well known and I haven't heard anything bad about their tunes. I've never dealt with Audi tuning before but I believe that company offers off the shelf tune options which can be further be modified but an authorized shop. That's what a local shop, Bluewater Performance, did with my car. The car definitely has proper parts and supporting upgrades. It has a GT2871RS turbo, Deka 80lb injectors, larger fuel pump, intercooler and so on. And it was tuned accordingly. However, the wide-band always read lean. The shop said my wide-band was faulty and the used their own, which was reading correct AFR's. Who knows. I kind of want to try a completely different ECU and tune but that seems like a waste of money.

How do you like being a mechanical engineer? I'm in school for that right now. Taking a calculus II course over the summer which isn't great but I'm hoping to just get through it. I haven't really had the chance to talk to very many mechanical engineers in person.


07-22-2018, 10:43 AM
Hello again.

Nice setup man! Gotta get that running right!

So U.M provided the map witch Bluewater installed and fine tuned? Correct?

I went to U.M. site to check their products.


Do you know witch one you have? Neither one are specced for 80lb infectors. If you have wrong fuel pressure, wrong injectors and faulty wideband your ecu is getting majorly fooled/tricked hehe :P No wonder it runs faulty if thats the case.
I MIGHT be wrong about this but by pulling the cable to the throttle body I belive that the ecu run on "manual/preset" numbers and neglects the sensors. This is what happens when you pull the wideband, it runs on pre-set known rich afr settings.
See what happens if you unplug the wideband. If it runs better the wideband is 100% fualty. Its the same idea with the MAF sensor, try that aswell.

Look into buying something like this. https://www.ebay.co.uk/itm/NEW-AEM-X-Series-Wideband-UEGO-AFR-Sensor-Controller-Gauge-30-0300-LSU-4-9/121978632419?epid=1652230613&hash=item1c667e38e3:g:JrkAAOSwsO1aslfJ

About trying another ECU, this is what you can do..

Buy a used ECU, take your current ECU + new(used) one you bought to an electrical shop. Make them install a socket for the chip where the chip for the tune is. Check this.

In sweden I can buy a used oem ecu for 30-60$, the electrical soldering job should not take an hour for an professional. Ask/look for someone who solders on boards. So say 100-120$ dollars. Might be worth it.

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Either way, the guy I talked with about my E85 setup strongly suggested getting adjustable fuel pressure and A/F ratio sensor, makes senso imo.

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Well, im no carrer person. Im working with construcion calculations at the moment. A degree, in my experience, isnt worth much. I mean if I would have started working at SAAB Gripen ( fighter plane facility ) I wouldnt know much enought to be productive. I would still need to learn aaalot at the new job. And after a couple of years you have forgot alot form the education. What the education gave me was a much better general understanding of mechanics and machines and the best thing a way of thinking, looking for and solving problems. So the education is more or less a papper proving you are capable of learning advanced stuff and what education you have where your intrests lay.

Where I leave (small island, Gotland) there is only 1 production facility/company so almost no engeneer jobs available. I worked there but the community was like stepping back into the 70is. Alot of racism, alcoholics and stuff liked that so said fuck this shit. Now im wokring as a consultant calculating big constructions and handling the projects mosly buildings with a colegee. We are starting some side buisness now aswell. So the mechanical engeneering is mostly applied on my hobbies these days haha :P

Best regards Hannes / Sweden

07-23-2018, 10:14 AM
So was the car running correctly when you first got it?
What changes have occurred between then and now that it's not starting/running right?

If you haven't changed anything on the car yet, I would first try to get it working with current equipment before starting to change components. You could simply make things more complicated to figure out if you start changing things without first diagnosing the issue.

If I had to guess based solely on your description of the issue I would say some sort of leak is occurring somewhere on your vacuum/intake lines.
For example, if the charge side of your intake is loose it could prevent the car from starting entirely.

07-25-2018, 07:59 AM
Hi everyone:

I'm not expert in the matter, but first thing it comes to my mind is trying another ECU so you can be 100% the blame it's on yours. Take a look at these guys (https://www.cartechelectronics.com/ecu-rental), they offer an ECU rental service. Don't know if it will be too expensive (considering the distance) or even if they ship to USA. But you get the idea.

Another thing you can do, as Bleuw said, it's to buy and used ecu and make a chip swap. And then test your car with that ECU. If the same problems still appeared, then the problem is somewhere else...

However, if for some reason you get to be 100% sure it's a unit problem, you can always buy a refurbished one with the immobilizer system off here (https://www.ecumotorstock.com/en/12-ecu-store).

But as others have pointed out, before taking any further steps, you should really run some diagnostics in order to discard anything else.