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2.7T Hard start when warm??? Need Help

2.7T Hard start when warm??? Need Help

 
Old 07-13-2018, 01:10 PM
  #1  
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Location: Edmonton, Alberta
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Default 2.7T Hard start when warm??? Need Help

Hi All first time poster. Wanted to say thanks for all the great advice I have previously searched that has been spot on.

First the car 2003 Audi Allroad. 2.7T 6spd, lightened flywheel, rs4 clutch, XS power turbo back exhaust(no cats), SAI delete,
upgraded intake boot, upgraded diverters.

THe problem when car is warm it turns over but takes a long time to start. Only after car has sat for more than 15 mins or
so. Problem will continue until car is cold and no heat is present. WHen is starts it struggles then idle normals out. No
noticiable driving quirks. Engine temp sensor shows correct on vag com and engine speed sensor shows rpms while cranking (200 rpm)

Car shows no codes related to start. (one for intermittent overboost, and SAI codes, oxygen sensor codes (unplugged rears
since no cats, one was bad) THe oil temp is warmer than it use to be 120c while driving (use to be 90c still high even with
egt unplugged) and even though the dash say 90c temp is 96 to 103 while driving. It goes up to 108 or so when the car is
turned off. Car also has an intermittent overboost and at WOT feels like you hit a lag...

Problem showed up after I removed engine. While engine was out I replaced timing belt, water pump and thermostat, Fill
screw was sieze i did have air but i believe i got it all out. Replaced chips in egt sensors, New fuel regulator, filter,
injectors sent out ultrasonic clean and tested, new rs4 clutch and pressure plate and fidanza lightened flywheel, SAI
delete and capped with 034 motorsports caps, XS auto downpipes with cat delete, valve cover seal replacement including
seals for cam tensioners, fuel filter. Thats all i can think of off hand.

So far I have swapped fuel regulator, pump is 4 years old still pushing fuel past the regulator easily. Cleaned throttle
body and run a throttle body adaptation. Cleaned intake temp sensor. Disconnected MAF but problem persisted. Replaced
engine temp sensor (4 wire one) (found air in the system). Ran with and without rear oxygen sensors connected. Disconnected
EGT sensors

Thats all i can think for now. Any ideas or suggestions are welcomed
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Old 08-28-2018, 04:43 PM
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So I replaced the CPS as it was suggested to me by several members but alas no dice.

I am thinking I have a temperature issue. The car always says 90C (194F) on the dash but in VCDS the ecu says 97C - 100C (206F - 212F) When I turn the car off the temp goes up and I have seen it go all the way up to 115C (239F) on the ecu once the engine is off. Is it possible that I have an air pocket in my coolant system and its causing the sensor to misread (steam) and thus not give enough fuel to start warm. I was thinking of checking my injector pulses (length) through the range and see if they are short during my hard start period and the car is starving to fuel. (if I even can with the car. Haven"t used VCDS too much) Anyone ever had a problem similar? There was air pocket around the sensor originally when I swapped it and I opened the reservoir and assumed that it was all pushed out and it started better but the problem persists.

I will report back once I run some more test. Car doesn't come to work with me so we don't spend lots of time together, it may be a while...
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Old 10-29-2018, 09:28 PM
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Skimmed volume of posted content and suggest possible classic Coolant Temperature Sensor issue recommend replace Green Top Coolant Temp Sensor G2 / G62. Four Pin two sided sensor reports coolant temp to dash gauge and separately reports coolant temp to ECU, and one type of common failure is engine side of sensor fails causing hard warm starts while dash temp reports no issue.

Last edited by AudiAllTheWay; 10-29-2018 at 09:34 PM.
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Old 11-20-2018, 12:50 PM
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Thanks for the feedback. I have replaced that sensor and I used one direct from the dealer. It made little difference when I swapped it, starts got a little better. The one I have currently is a green one. Is it common to get faulty sensors? I know people have complained about the cheap ones causing issues, I thought the dealer ones were the way to go.

My CPS sensor is also a cheap one because I didnt believe it to be the issue and they didnt have the brands I wanted anyways. I did notice however after I replaced that I started having multiple and frequent misfire issues. I replaces a couple coil packs with spares and swapped plugs and the issues went away. I dont understand how changing the CPS brought out misfire issues at all. The spark plugs I was using however before the swap I could not find much positive about those but they showed as if the car was running lean.

I am kinda at my wits end with this issue, I'm spending more time car shopping than trying to solve it, but still happy to hear if anyone has ideas or suggestions
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Old 11-20-2018, 01:06 PM
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Dealer CTS is a good one no worries there.

I use OE or OE Supplier Bosch Crank Position Sensors and Bosch or NGK Spark Plugs correct part number and heat range for your engine, and again never had an issue other than high mileage requiring replacements.

I never mix brands of coil packs esp OE and aftermarket, too many bizarre issues and prefer OE or OE Supplier.

It is normal to have a heat bloom after engine shut down, and it is also normal to see ~10 degree coolant temp difference between dash gauge and vag com. Vag com is accurate and dash gauge has built in 10% hysteresis. Dash gauge will let you know if coolant temp is low or high but they display 90C for consistency even though coolant may actually be 85 or 95 etc.

Immediately after engine shut down do you hear the secondary electric coolant after run pump running for several minutes? If not then after run pump has failed and there is no code unless harness shorted or open. Most 2.7T's after run pump are underneath intake though some late model Allroads mount on passenger side lock carrier area.

Is the thermostat installed properly? Some people don't realize the thermostat has to be clocked for small ball bearing air bleed passageway to be at the top.

The 2.7T's self burp coolant system fairly well. If unsure remove 3 screws hold reservoir high as possible while someone rev's the engine say 3K RPM for a minute or two.

Last edited by AudiAllTheWay; 11-20-2018 at 01:16 PM.
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Old 11-20-2018, 01:44 PM
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So here goes

CPS was replaced with cheap one. No OEM of Bosch available where I was. I was just changing it to see if it made a difference but i didnt believe it to be the culprit. Still have original

Plug were Bosch when this started. These ones to be exact
https://www.ecstuning.com/b-bosch-pa...of-six/7402kt/
Car started misfiring directly after the CPS change I replaced a few coil packs with extras I had (grabbed of someone doing an upgrade OE) and I put in some NGK (BREK6 IX) which eliminated all the misfire issues. Not sure if that is the correct heat range however?

Coil packs are all OE

I did the thermostat. Cant say 100% its correct but I believe it is and it shouldnt affect my start should it?

Dont think I have ever heard the secondary fan come on as long as I have owned the car. I believe it is under the intake manifold but I dont think it not running will affect my start either.

Now I am merely guessing based on my knowledge so if I am wrong in my assumptions definitely let me know, cause my goal is not only to fix this damn thing, but learn something
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Old 11-20-2018, 02:28 PM
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Comments about correct clock of thermostat install is in response to your questions about air pockets in coolant system. If air bleed hole is not at top then it could be possible to have air pocket trapped at thermostat causing over temp before thermostat opens. Thermostat opens based on coolant temp and coolant will be way over temp if hot air trapped pocket is trying to open thermostat.

Electric coolant after run pump under intake is important. It is not a fan as it is an electric motor with a wet end fluid pump. With parked area quiet and especially with hood open you should definitely hear the electric motor "whirring" underneath the intake immediately after engine shutdown for several minutes until coolant temp sensor says to shut it off. This is to continue circulating coolant through the turbochargers so that shutdown heat bloom does not coke engine oil in the turbo oil feed lines which if continuing will be the leading cause to turbocharger failures, including new turbo failure after replacement if coked lines are still present. Fix that then see how it runs and to save your turbo's. Maybe hard hot starts is because coolant is too hot from heat bloom?

Last edited by AudiAllTheWay; 11-20-2018 at 02:32 PM.
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