Tuning Engine has flat spot . Help needed.

[Jaybe]

Hi all . I hope someone out there might be able to point me in right direction. I have just bought a 2014 fiat Punto 1242 8 valve . Problem is when car is cold or normal running temperature it has what I say as a flat spot when pulling away. There is a hesitant before it pulls away which isn't fun crossing busy roads. I ve put my OBD 2 reader on it and I get "can't communicate" I've changed plugs done the cambelt air filter ect. (It was like it before belt change) I am an ex motor mechanic but not good on electrics ( old school mechanic) I am hoping it's just a censor somewhere. Thanks in advance. Jay

 

[GrandePunto PL]

Use USB interface (like ELM327) and Fiat specific software (FES, MES, AlfaOBD) and see the parameters related to timing (VVT and camshaft positions) and basic parameters (temperatures, pressures). First VVT(1) position should be around 106 degrees and control "closed loop" (not "excessive advance").

Power lag can be caused by malfunction in VVT (dirty solenoid valve and/or dirty/worn VVT wheel, internal leakage), old, weak ignition coils (charge time/dwell over 2,0 ms on idle) or exhaust (dirty lambda sensor, response time too long, although it will still pass the MOT, but on the lean side).

Plus the most neglected thing ever in 8V units: valve clearance/lash (0,30 mm intake, 0,40 exhaust)! Tight tolerance, let's say ±0,001" (±0,025 mm).
Camshaft lobes can wear too (1,4 8V has 9,50 mm lift on all lobes, but 1,2 8V is probably 9,00 and 9,20 intake/exhaust or other way round).

Check the fuel pressure (3,5 bar).

Exhaust system (especially manifold - broken studs) leaks. All things above contribute to: power loss / stalling / rough idle / emissions fail.

PS
Something for "old-school" guys. THIS is how you really Diagnose (capital "D") the cars!
https://www.youtube.com/c/AutomotiveTestSolutions/videos No parts swapping!
But oscilloscope is not "new" at all. Tools like that (minus pressure transducers) were available from the 70's/80's...

 

[Jaybe]

Use USB interface (like ELM327) and Fiat specific software (FES, MES, AlfaOBD) and see the parameters related to timing (VVT and camshaft positions) and basic parameters (temperatures, pressures). First VVT(1) position should be around 106 degrees and control "closed loop" (not "excessive advance").

Power lag can be caused by malfunction in VVT (dirty solenoid valve and/or dirty/worn VVT wheel, internal leakage), old, weak ignition coils (charge time/dwell over 2,0 ms on idle) or exhaust (dirty lambda sensor, response time too long, although it will still pass the MOT, but on the lean side).

Plus the most neglected thing ever in 8V units: valve clearance/lash (0,30 mm intake, 0,40 exhaust)! Tight tolerance, let's say ±0,001" (±0,025 mm).
Camshaft lobes can wear too (1,4 8V has 9,50 mm lift on all lobes, but 1,2 8V is probably 9,00 and 9,20 intake/exhaust or other way round).

Check the fuel pressure (3,5 bar).

Exhaust system (especially manifold - broken studs) leaks. All things above contribute to: power loss / stalling / rough idle / emissions fail.

PS
Something for "old-school" guys. THIS is how you really Diagnose (capital "D") the cars!
https://www.youtube.com/c/AutomotiveTestSolutions/videos No parts swapping!
But oscilloscope is not "new" at all. Tools like that (minus pressure transducers) were available from the 70's/80's...

Thanks from an old guy. I can't remember if I have a pressure tester. I think I shall probably agree on that it could be coils. It's like it could be them . I only just put a new cam gasket when I did the belt. I don't have Variable Valve Timing on this I do in my MGF though. Lamba could be questionable. Thanks though mate .

 

[GrandePunto PL]

Punto "EVO" and "2012" must have VVT to met Euro5 specs!
Only oldest Grande 1,2 8V didn't (1,4 did).

To get familiar with the model, here's an early service manual (Italian) for Grande.
http://www.fiat-bg.com/Downloads/Books/Grande_Punto/Fiat_Grande_Punto_Service_Manuale.pdf

 

[Jaybe]

Punto "EVO" and "2012" must have VVT to met Euro5 specs!
Only oldest Grande 1,2 8V didn't (1,4 did).

To get familiar with the model, here's an early service manual (Italian) for Grande.
http://www.fiat-bg.com/Downloads/Books/Grande_Punto/Fiat_Grande_Punto_Service_Manuale.pdf

I can't translate this. So what operates the valve timing ?? When I had the cam cover off I didn't see any cam adjuster/switch inside. Where will I find it and how do I check the switch ( if one fitted ) ?? I have a workshop manual and will have a look while someone can point me in the right direction. Thanks guys n all

 

[GrandePunto PL]

Dear "ex-mechanic", you don't have to translate anything. Pictures alone are enough to grasp what's going on.
Study the PDF file, whole "1,4 8V" section (because future 1,2 8V will be the same design and parts location).
There are detailed pictures of timing belt system, VVT wheel (even disassembled), VVT solenoid valve etc.