I've spent about 3 days getting my 3.8 to run properly. I've had lots of help from bexley motorworks and Farrell.
The problem I had was one that quite a few members have had in the past - surging on constant part throttle.
Mine got so bad that the car was beginning to become undriveable. After changing the o2 sensor and the MAF the car drives really nice but there is still a small amount of surging. It's not enough to be really noticed.
My o2 sensor was reacting too slowly and this was causing surging throughout the rev range making the car horrible to drive.
What I want to know is do your 3.8's:
1) Drive smooth under constant throttle at high speed in a high gear or is it ever so slightly jerky
2) do they slightly surge when in a low gear and highish rpm on constant throttle
If you don't know the answer then please do make a point to test this when your driving next.
Thanks
Sal
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Avus Blue 6 speed 3.8L E34 ///M5 Sedan
Evolve ECU Remap / Chip | Evolve Carbon Intake | Powerflex Black | Whiteline | Eibach Springs
I've had surging Sal.
Exactly as you describe, but after the mods it is barely discernible, I would like to see if it is still there - but you will have to wait till April as the Beast hibernates.
Quite the same for me. Not all that bad, but very noticable. I had the plugs replaced and an injector replaced. Next I need to look at the O2 sensor I guess.
Mine used to doit. It was only at low speed and low throttle. It was hardy noticable and I mean hardly. You would have to really pay attention to realise. I was told by many people that, that little bit is nothing to worry about, its normal for this type of engine. Obvioulsy yours was alot more severe.
Over 2 years ago mine started to surge pretty badly. New MAF made it almost negligible then over the course of the following 6 months it started to come back. Tailpipe started getting sooty within a couple days of a wash; identified a leaky injector. Replaced all 6 and cleaned the intake tract along with replacing FPR while there and the car is rock stable.
Iīm working on one right now, at high rpm in 2 -3 gear itīs surging but not in 5 gear. tryied to disconnect the oxygen sensor and the car runs perfect. The oxygen sensor is new and is fast.
If I install a resister on 1 k for water temperature, so the control thinks itīs about 50 to 60 degrees, then itīs running great again. this sensor is new.
Injectors and MAF are okay, throttles are synchronise.
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Bay
1995 ///M5 Diamont black
1995 ///M5 Avus blue
1993 ///M5 Avus blue 3.9l
There is a little low speed / low rpm surge inherant within the std 3.8 calibration.
This is a function of emissions / cold start calibration that is present at idle (950 rpm) to fast idle at 2,400 rpm which coincidentally is where the additional calibration switch point exists within the DME 3.2 ..!
It will be highlighted by older components wearing out.
By the time you have done 180,000 kms, you may want to consider checking the following.
Oxygen sensor & wiring.
Crank position sensor can get dirty & can be cleaned with miraculous results.
Water jacket temp sensor & wiring(usually brittle)
Maf sensor which based on age alone is likely to be past its best.
(Lumpy tickover & reluctance to idle from cold followed by general overfuelling throughout the rpm range.
16-17 mpg at normal motorway speeds is a good indicator.
My Maf started to fail @ 240k kms miles but I think this to be exceptional & a function of generally long journeys that the car was used for.
Coil pack management units are often overlooked.
They dont all fail at the same time.
I have replaced two in the last 5 yrs.
They really can screw with your head when trying to diagnose part throttle misfires.
Typically, a good idle but poor part throttle repsonse under load..
Also the power wires to the coil packs can get damaged by careless refit of wires to the tracks & subsequent replacement of the cover chafs the wiring..!
Split / perished vacuum hoses is another favourite that is often overlooked.
I am not going to cover fuelling here.
Mark D'sylva's work with the eprom for the 3.8 is reputed to smooth the low to mid range rpm to the switch point at whic the resonance flap turns.
The goals of getting through passby noise & emission test bring many restrictions to the o/e that the aftermarket can improve.
I hasten to say that extended rpm limits is not one of them imho.
Even now, my car surges a little.
For obvious reasons, its worse on a cold spring morning when the aircon is engaged to assist the demisting of the windows.
My 3.6 used to do this, along with having poor fuel consumption, and lacking top-end power. I spent 6 months tracking the problem down. We replaced all of the vacuum hoses, replaced the gaskets on the inlet manifold, replaced the air pipe between the MAF and the plenumn, cleaned the MAF, cleaned the injectors twice, replaced the fuel pressure regulator, replaced all of the fuel lines, replaced the 02 sensor, replaced the fuel filter, and after all of that, it turned out that the fuel pump had a developed a crack in it which was causing cavitation in the fuel. After we replaced the fuel pump, it ran like a dream again.
I was so close to selling my car when it was running like this, it was really getting me down, and we just seemed to be throwing money at it but we couldn't figure out what was wrong, and it was like that for 6 months. I'm glad though that we replaced all of the vacuum hoses, most of them were brittle, as were some of the fuel hoses that we replaced, and the big air pipe turned out to have a split in the bottom of it that we had never noticed before, so a lot of the stuff we ended up changing was for the best anyway. The fuel pressure regulator, and the O2 sensor were expense, and not needed as it turned out, so now I have some spares :-)
John
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My E34 M5: http://www.jrobbo.com/M5
License Plate: "EUROM5", VIN: "GA25294". Come and get me!
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