StevenL5975

Hello,

Well there is that '91 S5 T2 we did recently rebuild which still has a few issues. Engine is stock with RA seals and streetport, internals and tolerances are fine.
That was a quality rebuild, there were still some minor things to improve but this should be a pretty strong engine. We could get it running but the turbo was blown (burning oil) so it has been replaced with a stock used one. Running around 300 ml premix on the tank with stock omp.

The car has a fuel cut defender and custom build coolant radiator with e-fans. Stock intercooler. Blow off valve is aftermarket. Exhaust system consists of the stock turbo with downpipe and precat. Custom build mid silencer and then Y pipe, no mufflers at the tails.

It starts relatively fine and does not hold any idle at all, (warm or cold) I have to play with the accelerator to keep it from stalling. Oil pressure and engine coolant temperature are in normal range.
If I take it out for a drive it has a constant slight hesitating through the entire rpm range. Sometimes the hesitating is gone for a short time, but I could not relate it to anything, seems randomly.
It rarely generates boost when accelerating, sometimes a bit but never above horizontaly on the gauge. While accelerating it does backfire like a damn old gatling gun, not really that loud but very rapidely, well just like a machine gun

When driving behind the car I can see the exhaust backfiring and the silencer / Y-pipe combo is glowing red under the car, tailpipes have a light bright brownish color inside, not black like on my S4 NA. We did stop the test drive once the exhaust system started to glow red.
I did test the timing on he engine, couldn't really get it to idle halfway decent (in fact it doesnt idle at all, its a pita to keep it running) T1 seems pretty close to the left timing mark but as the engine doesn't idle I cant confirm this, L1 does not fire at all.
After messing a bit with the plug wire it does fire sometimes. So There are 4 plugs of which L1 is not firing as it should and I am suspecting the engine to run way too lean or too rich due to a glowing exhaust system and brownish residue on the tail pipes.
The plugs are good, tested another one for L1 and that doesn't change anything.

When I sat in the passenger seat I had a feeling as if the engine wasn't running smooth, in terms of ignition and fuel. Once the backfiring starts I feel as if the car hesitates between boosting and backfiring, some kind of weird shaking. There was also a slightly hissing sound, I dont think that this could have been the turbo charge going to waste, it wasn't loud enough for that. Might be something else. Or its just normal on a T2, I don't know as I only drive NAs As for the L1 plug wire, I am pretty sure its screwed up, but I don't know if that will lead to the symptoms described. I tested the wire with around 17k Ohm and redid all the connectors (clamping them tighter)

Does anyone have an idea why the turbo is not charging and where the glowing exhaust system comes from ?
Any help is appreciated.

Best Regards
Steven

RotaryEvolution

iTrader: (30)

replace your plugs and wires.

a slightly off injector clip will also give similar results. backfiring is due to unburnt fuel pooling in the exhaust pointing mainly to a faulty plug not firing one rotor or an injector dumping wayyy too much fuel.

satch

iTrader: (1)

Just pull the spark plug wires off of the leading coil bore and place the wires such that they are barely touching the coil bore and then check for spark at both bores. If it is present then your problem is from the wire and or the plug.

StevenL5975

Many thanks Karack !

Yes, thats what I told him to do, change the wires as they are still OEM on that car.
I think these ones would do the trick: http://www.corksport.com/magnecor-10...lug-wires.html

A set of new plugs could be installed too, I proposed to use new plugs, but he wanted to install some used ones ... They are still good, but a new set won't break the bank.

With injector clip, you are referring to the electrical connector on the injector ?

Thanks
Steven

walken

iTrader: (6)

boost leak/vacuum leak and a TPS out of adjustment will cause the same thing.

StevenL5975

Hello again, I got some updates on this topic

Today I installed a wideband on the car, its a AFX NTK.
Wideband is properly calibrated and shows AFRs around 13 to 16 (16 = end of scale)
The car bogs and backfires at around 3800 rpm @ AFR:16.00.
So for me thats clear, the car runs dead lean, around 13 to 14,9 at idle (well there is no real idle) and AFR: 16.00 on full throttle at 3500 to 4500 (I cannot rev it any higher).
Maybe the secondary injectors do not come on as they should ? What would cause that ? Debris ? Bad connectors ?

We will try to adjust the TPS asap, today we were busy installing the wideband to see at what AFR we actually are. Spark plug wires won't be replaced, the owner does not want to.

Steven

Edit:
Oh yeah, I tried to pull the ECU codes, jumpered the green wire to GND but there is no CEL flashing. Its a S5 but I cant see a CEL. Even with the key to ON there is none. Maybe bad bulb or did I something wrong ?

j9fd3s

iTrader: (3)

1. i'm not sure the euro cars have a CEL, the JDM ones don't. you can get codes still, but you use the diagnostic connector, the procedure is in the FSM (i don't recall it!)

2. you can check the wires with an ohm meter, they should be under 16K Ohms per meter, and since they are a meter long, its easy...

StevenL5975

Ok, I will check the CEL thing. The cables are in spec, I tested them with a Multimeter. The problem with them lies with the connectors, they are somewhat loose.
The main problem lies somewhere with the fuel system, its running dead lean and we dont know why. There is no boost too.

Steven

Molotovman

iTrader: (49)

Shot in the dark, have you ruled out limp mode due to a bad OMP?

jimmydanny

I get these symptoms when my ECU is water damaged:

No idle
Backfire and just fire from the exhaust when decelerating. The first I get on accel and decel.
No power
Can't rev above 4-5k warm or cold
Engine dies real easy, dies instant with full throttle.

It is close to limp mode in how it acts, but it doesn't idle at all and dies really easy. I can't get above 0 on the boost gauge (in other words atmospheric pressure)

EDIT: And yeah, it has never started as easily as it does now, for some reason. I wonder if it is the same as limp mode, it only uses the leading coils and plugs to ignite? That might be why the leanyness and backfire combined?

j9fd3s

iTrader: (3)

my Rx8 has the loose connector thing, i just took some pliers and gently squeezed the clip, so now its tight enough to stay on.

stab in the dark, you should try resetting the ecu by unplgging the negative cable and stepping on the brakes, its possible (maybe likely) you set some crazy codes before the car was even started. i remember we had an FD at the shop once that had a ton of codes and ran like crap, and it turned out the tech had turned the key on with one of the ecu plugs unplgged, and it set like half the codes....

reset ecu, and it was happy. although i'd still suspect a mechanical problem too

myfc3s

iTrader: (2)

When you installed the engine harness, did you check to see if you may have installed the primary wire/clip to the secondary injectors, Also check for air leaks from the intake and check the Air mass sensor. Im only saying this by experience when i had the stock ECU and this was many many years ago.