1.6 Gti Engine Set-up

[shepherdfte 0]

I'm having a few power probs with my 1.6. She is generally very fit, godd compression, mechanically quiet, and the cam train looks good with correct clearances. Uses no oil. I think the ign is fine (mostly new and I've had 3 dizzys), and I've done the timing. It advances when it should etc.

 

But my top end power is very variable. When cold and luke warm, she seems fine -really pulls well, and reves out well (not that I like doing that on a cold engine). But when hot, it often feels a bit flat, and is reluctant to really rev-out (feels uo 3-4k, but over that it feels like your thrashing it. But then if you really kick its backside for a bit (like on a rally), the power seems a bit better.

 

I wondered if the water temp sensor was playing up, but it is new. What tests can I run on it, and could I put a resistor in instead of it to fool the ECU into thinking it was always hot, just to check? Any other ways of checking?

 

What else could it be?

 

Other than that specific problem, my plan is as follows:

 

1) Get injectors cleaned

2) Double check ign set-up

3) Re-track AFM and check it and the throttle pot resistances etc

4) tune the idle

5) get it set up properly

 

Is this a good plan, but more importantly, what do people mean when they say 'get it set up properly' (as often posted)? I know what can be adjusted for the idle (afm bypass, throttle pot screws x2 - this I can do), but what the hell do people adjust for the remainder of the range? If I took it to a good tuner, what would they be able to change? The only thing I can see is the spring in the AFM?

 

Also, (assuming we can figure out what I need!) can someone recommend a tuner (better still one with a rolling road and a good understanding of 205s and mixture set-up) in the Salisbury/bristol area? Preferably one who will listen to me!

 

cheers,

 

Andy

[shepherdfte 0]

Oh yes - forgot to say, also getting terrible fuel consumption. About 20mpg driving normally to work etc, getting slightly BETTER on a rally or fast a-road thrash. Still awful on the motorway.

[Rob_the_Sparky 9]

Well if it is a fairly standard engine then I'd look at what is causing the fuel consumption problems first as this is terrible. a good 10mpg down on what you should be getting on a work drive.

 

Cleaned injectors has made a difference to the top end on both the 1.9s I've done it on but has made sod all difference to the economy. If you are doing the injectors then you could also replace the FPR while you are at it. It is possible this is set-up wrong but so few people have checked the fuel rail pressure that I can't tell you how likely this is although it is easy to change once the rail is off.

 

A duff vacuum advance will loose you a few mpg so might be a problem (both the spare dizzys I have have got bust advance units!). This made about 3mpg difference to my 1.9 so clearly this can't be your only problem.

 

AFM I guess is the only other likely culprit for excessive fuel consumption given that you have aleady done the ECU temp sensor.

 

Rob

[shepherdfte 0]

Well if it is a fairly standard engine then I'd look at what is causing the fuel consumption problems first as this is terrible. a good 10mpg down on what you should be getting on a work drive.

 

Cleaned injectors has made a difference to the top end on both the 1.9s I've done it on but has made sod all difference to the economy. If you are doing the injectors then you could also replace the FPR while you are at it. It is possible this is set-up wrong but so few people have checked the fuel rail pressure that I can't tell you how likely this is although it is easy to change once the rail is off.

 

A duff vacuum advance will loose you a few mpg so might be a problem (both the spare dizzys I have have got bust advance units!). This made about 3mpg difference to my 1.9 so clearly this can't be your only problem.

 

AFM I guess is the only other likely culprit for excessive fuel consumption given that you have aleady done the ECU temp sensor.

 

Rob

 

Magic thanks. Should have said actually, I checked the rail pressure (gucci new tools ) and it's exactly 3bar, drops fractionally as the throttle is blipped but recovers very fast. I'm pretty sure the vac advance is working.

 

Any ideas what can be adjusted if I get it on a rolling road?

[richsmells 2]

Hmm, i reckon mine could be the same. Really odd. Check you don't have a crack in your exhaust manifold as it could open up when the car gets hot leaving you a little down on power.

 

Not sure about fuel consumption though. Mine was really bad, but since i've had the car back from the MOT it's been rather good. It must have been adjusted.

Edited May 24, 2006 by richsmells

[Rob_the_Sparky 9]

Intended adjustments are limited to the idle mixture and the ignition timing. However, it is also possible to play with the mixture by adjusting the AFM spring tension but not recommended unless you have a RR to check what is happening to the mixture across the range.

 

If you get a "chip" then you can adjust fuel mixture this way as well but again it is an across the board adjustment.

 

So your choices for adjustment are very limited. At least a quick RR session may tell you what is probably wrong.

 

Rob

 

P.S. Fuel rail pressure is relative to the manifold pressure, the more depression in the inlet manifold the lower the rail pressure.

[shepherdfte 0]

That's what I thought. Limited adjustment. So I need to fix/check everything I can, and then get it on a RR with a gas analyser.

 

So back to one of my questions - what can I check to ensure the ECU knows the engine is hot? I can check the water sender as per the Haynes, but what else? Can I frig it to fool the ECU into thinking it's hot?

 

 

and rolling roads:

 

Any good ones Salisbury /Reading/Southampton/Bristol way?

 

 

Thanks for all the help

Andy

[shepherdfte 0]

Oh yes - manifold and exhaust and relevant gaskets all new, and standard.

[Rob_the_Sparky 9]

The ECU on these cars is not like a modern digital system, it is closer to an electronic carb, e.g. the ECU will "know" nothing! The amount of fuel added is a direct function of the sensors, unlike a modern system where it is indirect via a map.

 

As long as the sensor is good and the wires from ECU to sensor are good then there is no more to check. You certainly can frig it and this is not an unusual thing to try but like all other mods it is an across the board change (done by adding resistors either in series or parallel). However, given that you car is standard you are better off finding what is wrong rather than frigging your way around an existing problem. Generally these cars fuel very well (with the exception of idle) so there should be no need to frig anything on a stock car.

 

Rob

[steve@cornwall 100]

SAD not closing or leaking pipe from same-only suggest 'cos it sounds like the symptoms of a sticky choke on a carb.

[shepherdfte 0]

Agree I'd like to find out what's wrong - just wandered about bypassing things as a fault finding exercise.

 

No SAD to go wrong - I have a little air-valve in it's place which I can switch on or off. It works fine, and the problem exists regardless of setting.

[shepherdfte 0]

Just looked at my 2 Haynes manuals with a view to testing the coolant temp sensor. Not very clear as it just says 2 resistances for the 'temperature sensor' (at 40 and 96 degrees), with no picture. I know where it is on the car, but is that the right info for the right bit of kit?

 

ta

 

Andy

[Rob_the_Sparky 9]

No idea TBH, I've just replaced them when in doubt.

[shepherdfte 0]

Ah well - reckon I'll do that then!

[shepherdfte 0]

Ok, done several of those things - retracked AFM, changed water temp sender (old one checked out fien on the bench), new leads and dizzy + cleaned up the nearly new plugs. Compression 10.5 (155) across the deck, although one pot was a bit lazy pumping up. Oh yes, and the 2 year old vacume advance/retard was foobared (grrr), so I changed that.

 

One question though. I strobed the timing. Mine seemed to be what Haynes calls the 'earlier model' (E reg), in that it only has one flywheel mark, so this needed to be timed at 700rpm to the BTDC mark, rather than timing the second mark to TDC at 3500 as per the later cars. does this sound normal?

 

Worked fine, but required a huge change, and now my dizzy is surprisingly near the 'stops' in terms of advance adjustment. Car now feels much much fitter, but I'm worried it's over advanced. Doesn't seem to pink, although perhaps just for a sec if you dump the gas in 5th going up a slow hill at 30mph. does this sound right?

 

Have to wait on the consumption figures, and anyway, I've clean injectors arriving sometime this week.

 

Andy

[GLPoomobile 958]

Is a 155 PSI not a little low for the compression? I thought you should be looking nearer the 180 mark. I stand to be corrected though.

[Rob_the_Sparky 9]

It is normal that the engine is timing quite close to the end of max advance. I have made similar large changes to my cars when tuning by trial and error so certainly nothing to be worried about. My guess is that they have been heavily retarded to make them run on 95RON fuel.

 

Rob

[shepherdfte 0]

Sound - thanks Rob.

 

anybody else reckon 155psi is a bit low for a 1.6 115 engine compression?

[Rob_the_Sparky 9]

Dunno, a 1.9 will usually be around 180 (or more if tweaked) but not sure you can read much into the max value. It does sound lower than I'd expect but not sure it is a problem and I'm used to 1.9 readings.

 

Rob

[Pug_101 0]

Dunno, a 1.9 will usually be around 180 (or more if tweaked) but not sure you can read much into the max value. It does sound lower than I'd expect but not sure it is a problem and I'm used to 1.9 readings.

 

Rob

 

 

Did compressions on a 1.6L recently and got 12's in all cylinders. Engine was standard with penty of miles and no sign of rebuild.

[shepherdfte 0]

hmm. 12. Ah well, mine was 10.5 to 11 across the board, so it sounds a little low, but not overly so for a 130k motor.