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View Full Version : high LTFT, poor MPG, no fault codes?



Rob69
01-04-2013, 01:03 PM
Hi - re-posted this into this section today after no replies in POLO forum section, maybe more relevant to diagnostics forum!

Hi - first post for a good while and first in relation to current Polo - first petrol engine (http://www.shopzilla.co.uk/rd2?t=http%3A%2F%2Fstat.dealtime.com%2FDealFrame%2 FDealFrame.cmp%3Fbm%3D496%26BEFID%3D96425%26acode% 3D502%26code%3D502%26aon%3D%26crawler_id%3D1912009 %26dealId%3DhZoi7tf_70duUyasCd91wg%253D%253D%26sea rchID%3D%26url%3Dhttp%253A%252F%252Frover.ebay.com %252Frover%252F1%252F710-64684-24024-0%252F2%253Fipn%253Dpsmain%2526icep_item_id%253D12 1073581477%2526icep_vectorid%253D262531%2526kwid%2 53D1%2526mtid%253D635%2526crlp%253D1_262531%2526kw %253D%257Bquery%257D%2526query%253D%257Bquery%257D %2526linkin_id%253D%257Blinkin_id%257D%2526sortbid %253D%257Bbidamount%257D%2526fitem%253D12107358147 7%2526mt_id%253D635%26DealName%3Dzenoah%252Fcy%252 Ffuelie%2520petrol%2520engine%2520%2527failsafe%25 27%2520kill%2520switch%26MerchantID%3D424487%26Has Link%3Dyes%26category%3D33%26AR%3D-1%26NG%3D1%26GR%3D1%26ND%3D1%26PN%3D1%26RR%3D-1%26ST%3D%26MN%3DmsnFeed%26FPT%3DSDCF%26NDS%3D1%26 NMS%3D1%26NDP%3D1%26MRS%3D%26PD%3D0%26brnId%3D3139 %26lnkId%3D8060231%26Issdt%3D130328010152%26IsFtr% 3D0%26IsSmart%3D0%26dlprc%3D17.99%26SKU%3D12107358 1477&mid=104482&catId=13195&atom=11342&prodId=&oid=4893683878&pos=1&bId=18&bidType=0&bAmt=25e643bb8680d02f&cobrand=2&rf=af1&af_assettype_id=10&af_creative_id=6&af_id=11444) for a good while!

Car is 2005 1.4, 16V, 75PS, BKY petrol engine (http://www.shopzilla.co.uk/rd2?t=http%3A%2F%2Fstat.dealtime.com%2FDealFrame%2 FDealFrame.cmp%3Fbm%3D496%26BEFID%3D96425%26acode% 3D502%26code%3D502%26aon%3D%26crawler_id%3D1912009 %26dealId%3DhZoi7tf_70duUyasCd91wg%253D%253D%26sea rchID%3D%26url%3Dhttp%253A%252F%252Frover.ebay.com %252Frover%252F1%252F710-64684-24024-0%252F2%253Fipn%253Dpsmain%2526icep_item_id%253D12 1073581477%2526icep_vectorid%253D262531%2526kwid%2 53D1%2526mtid%253D635%2526crlp%253D1_262531%2526kw %253D%257Bquery%257D%2526query%253D%257Bquery%257D %2526linkin_id%253D%257Blinkin_id%257D%2526sortbid %253D%257Bbidamount%257D%2526fitem%253D12107358147 7%2526mt_id%253D635%26DealName%3Dzenoah%252Fcy%252 Ffuelie%2520petrol%2520engine%2520%2527failsafe%25 27%2520kill%2520switch%26MerchantID%3D424487%26Has Link%3Dyes%26category%3D33%26AR%3D-1%26NG%3D1%26GR%3D1%26ND%3D1%26PN%3D1%26RR%3D-1%26ST%3D%26MN%3DmsnFeed%26FPT%3DSDCF%26NDS%3D1%26 NMS%3D1%26NDP%3D1%26MRS%3D%26PD%3D0%26brnId%3D3139 %26lnkId%3D8060231%26Issdt%3D130328010152%26IsFtr% 3D0%26IsSmart%3D0%26dlprc%3D17.99%26SKU%3D12107358 1477&mid=104482&catId=13195&atom=11342&prodId=&oid=4893683878&pos=1&bId=18&bidType=0&bAmt=25e643bb8680d02f&cobrand=2&rf=af1&af_assettype_id=10&af_creative_id=6&af_id=11444), NON EGR. 69,000 mls. Ongoing problem is poor MPG (37-38) and lumpy idle around 6-700rpm, now that I've sorted other faults ( coil springs, brakes, water pump....) I've started to look at engine. All coil packs were changed around 15k miles ago.
Hooked it up to OBD scanner (Autel MS509), no fault codes present, but high LTFT, averaging mid +teens, STFT also tends to low +teens but occassionally dips to low -teens, during steady level road at 50-60mph. Engine temp stable at 85'C ( OBD readout, not dashboard)
Front o2 / AF sensor seems to have reasonable cross count (around 1/ sec)and reads between -0.1, +0.1mA except when open loop on engine overrun, but I'm struggling to find optimal mA range for this front sensor - maybe this mA range is too narrow / low????, sensor needs changing???)
Post cat o2 sensor (http://www.amazon.co.uk/dp/B004U0PC9A/) averages + 0.7 V and responds to throttle blips asI might expect.
I removed and cleaned MAP sensor (http://shop.ebay.co.uk/?_nkw=map+sensor) with CRC sensor spray, reinstalled it but no change to fuel trims, although car feels a bit snappier ( placebo effect maybe).
I've checked for vacuum leaks but don't suspect this to be cause as STFT & LTFT stays high even with throttle wide open and high MAP, MAP responds to throttle position. No sign of exhaust leaks. Throttle body (http://shop.ebay.co.uk/?_nkw=throttle+body) is clean as no EGR on this engine, no MAF sensor (http://shop.ebay.co.uk/?_nkw=maf+sensor) also.
I've read posts regarding Evap canister leaks but struggling to find info on the Evap system.

Can anyone offer any advice regarding high STFT, LTFT, O2 sensor (http://shop.ebay.co.uk/?_nkw=o2+sensor) optimal values (mA) and Evap system??
I'm not inclined to chuck new O2 sensor (http://shop.ebay.co.uk/?_nkw=o2+sensor) on without a bit more knowledge / justification.
Planning to do a compression test when Scottish permafrost eases off, may indicate blocked cat.

No immediate solution to this then I'll move onto sticking door locks, don't mention the aircon system.

Cheers

RobH

Doctle Odd
01-04-2013, 01:33 PM
MS509 is an OBD scan tool and NWAF on a VAG! Ross-Tech: VCDS: DTC Comparison (http://www.ross-tech.com/vag-com/dtc-comparison.html) It sounds to me like a CTS fault, if it's spurious it might not show a fault code but it will produce your symptoms. Cheap and easy fix if it is but get a proper scan with VCDS or a VAG scan tool

Rob69
01-04-2013, 08:58 PM
Hi Thanks for reply - point taken regarding OBD tool vs. VCDS!
I've had a faulty CTS on last car, old VW TDI which appeared to be working ok but gave excess fuel and glow plugs staying on too long at start up.
Any experience of VCDS - Lite, download, can you suggest suitable inteface cable??
will post results of scan or CTS change.
cheers
Rob

Doctle Odd
01-04-2013, 08:59 PM
http://www.gendan.co.uk/product_VAGUSB.html

S66MJETDI
01-04-2013, 09:42 PM
Is there a glossary for this thread?

Doctle Odd
01-04-2013, 09:56 PM
A glossary? Just norms innit bruv, but it's well kosher innit nowotimeen?

S66MJETDI
02-04-2013, 09:55 PM
I was serious..... Whats stft and ltft....... always happy to learn....

Doctle Odd
02-04-2013, 10:14 PM
My apologies, I was gargling yesterday (euphemism for sipping whiskey) I'm pretty sure its Short Term Fuel Trim, and Long Term Fuel Trim.

S66MJETDI
03-04-2013, 09:36 AM
Ah..... no offence taken..... I like a single malt 😉

Doctle Odd
03-04-2013, 09:42 AM
I like the pot still style so it's Bushmills or Beam but ne'er the twain (desperate hangover)

S66MJETDI
03-04-2013, 09:52 AM
Macallan or Jura for me ....... As for bad a bad head thats pretty much a given for me, I can't resist a mix and match session on the real ale at my local and that stuff seems to have a kick like a mule.

S66MJETDI
03-04-2013, 09:53 AM
P.s sorry for hijacking the thread :s

Doctle Odd
03-04-2013, 10:17 AM
:alcoholic

Rob69
03-04-2013, 08:04 PM
No worries - it's all Greek to me.
New CTS arrives tomorrow, should get it fitted and see any change, now looking for old laptop to install VCDS onto.

cheers