1,9 Rallye stuttering around 5500 rpm

[HoRSiCZeK 2]

Hi there guys,

 

I am writing in asking for advice about stutter on 1,9 LU2 Jetro Rallye

 

The car was bought with this problem, from first time it was having a stutter/misfire/milisec loss power or how to call it, ONLY at around 5500 rpm

 

The stuttering starts around 5300-5500 and keeps for about 500 rpm and after aprox 5800 rpm the engine goes again smooth

 

Knowing this whole engine was changed from another Rallye (which was running good there) ,but the stutter remain same, so I assume problem is somewhere around engine and not a "hardware"...

 

Also second engine has slightly sharper cam and different ECU, and even with basic ECU and sharper CAM stutter was same like on original engine.

(I am not totally sure if second engine had injectors in, and if had, if they were keeped in or changed for original ones) :///

 

We changed in years many times all basic components like sparks, distributor cap etc, and had several other issues with all that Jetro magic vacuum etc, but even after all the things changed and checked the same stutter remains.

For whole time each every sparks are black from too rich mixture, happened on both engines, and it can also be smelled. The fuel consmption is 205 GTi :)))

 

Last things we did not replaced are: fuel pump, lambda probe, AFM (and injectors - which I am not sure about if were or not)

 

Now after looking at site could our problem be the Ignition amplifier?

 

Could this be caused only by some air leak which we still did not found?

 

I assume that SAD doesnt play role in this high rev problem?

 

Thx for any advice

 

 

 

[jackherer 543]

2 hours ago, HoRSiCZeK said:

Now after looking at site could our problem be the Ignition amplifier?

It could be. It might even just need new thermal transfer paste on the heatsink.

 

Is it a genuine Bosch blue amplifier?

[Tom Fenton 1,542]

I once had very similar symptoms with a misfire through a certain rev range that if you drove through it, it would clear up. For me it was the ignition amp.

 

I was fortunate to have another running car so I parked them side by side and kept swapping parts over until I found what was causing it.

 

[HoRSiCZeK 2]

8 hours ago, Tom Fenton said:

I was fortunate to have another running car so I parked them side by side and kept swapping parts over until I found what was causing it.

 

Yup this was exact plan, sadly more running 88kw motros around hope someone will respond

 

12 hours ago, jackherer said:

It could be. It might even just need new thermal transfer paste on the heatsink.

 

Is it a genuine Bosch blue amplifier?

dunno exactly cause car is now on transmission change, will tell friend to look after it, he has access to buy new parts so maybe he will try new one

 

 

Any photo where to find this amp on 1,9 rallye?

[welshpug 1,661]

same as a gti, early cars will be on the left side of the car behind the battery, later cars on the opposite side by the engine mounting.

[Thijs_Rallye 87 4 Cars]

I've had similar issues on the former trackday car engine, but, started stuttering around 5500/5600 but that became worse and ealier in revs as time progressed / temperature rose. Found that an internal oil leak in the dizzy destroyed the isolation of the pickup coil. The hotter is became, the lower the revs were where the stuttering began. Switched dizzies and all was ok.

[bacardincoke 42 1 Cars]

On 6/9/2020 at 6:42 PM, jackherer said:

It could be. It might even just need new thermal transfer paste on the heatsink.

 

Is it a genuine Bosch blue amplifier?

I wouldn't have known about the thermal paste and the potential problems that not having it could be caused had it not been for this post.

 

I'd mine off for cleaning a while back and as there was no evidence of any paste I'd no idea it should have been there let alone replaced.

 

Also just read Damir's article on the subject... thanks both for the knowledge.

[opticaltrigger 52]

Yes, odd,,,

I suppose it could be the amp, but it would be strange for the transistor to be particularly struggling in a specific frequency range like that. Not impossible though, I suppose....

As Thijs mentioned above, it could be issue with your pickup coil or perhaps the screened lead from the distributor. But try an amp anyway if you haven't yet and see what happens, there not to expensive. After that, could be time for a new distributor unfortunately. 

 

All the best,

O.T.

 

Edited June 11, 2020 by opticaltrigger

[jackherer 543]

17 minutes ago, opticaltrigger said:

I suppose it could be the amp, but it would be strange for the transistor to be particularly struggling in a specific frequency range like that. Not impossible though, I suppose.... 

It's very common for 205 GTIs (and 1.9 Mi16s which use the same amp) to develop a misfire or 'blip' that can be driven through, normally around 4000-4500RPM*, that is caused by the amp itself either failing or simply overheating due to lack of thermal transfer paste.

 

I've seen it many times myself and it's been reported on here hundreds of times over the years. Why it happens at a specific RPM has never been determined but it definitely happens.

 

*205 tachos are often inaccurate so while the OP reports a problem at ~5500 RPM in reality it may be lower.

Edited June 11, 2020 by jackherer

[opticaltrigger 52]

Thanks K, I didn't know that.

I wonder what causes that.... If I get the chance, I think I'll try and find out exactly what components Bosch used in there and see if it sheds anymore light on it. I wonder if it could be a thing that's related to the distributor pick up coils as Thijs said above. We would really need to catch it on a scope to be sure I suppose.

 

O.T.

[jackherer 543]

58 minutes ago, opticaltrigger said:

I wonder if it could be a thing that's related to the distributor pick up coils as Thijs said above

The fault seems to be the same with either Jetronic 8v management or Motronic 16v with the latter using a crank position sensor and therefore triggering the amp directly from the ECU.

[HoRSiCZeK 2]

so hopefully, what I was hoping for, it would not be a bad distributor, but if new amp will not help, I will try this as next step ;)

 

thx a lot guys, gonna write u a result in few weeks I hope ;)

[HoRSiCZeK 2]

so car is back and looks like stuttering is gone! so amplifier change helped, thx guys!