Hard Start After Sitting Overnight

[promet]

i've recently finished installing the final piece of my hard-start ' mental puzzle ', a new camshaft position sensor

all recent components:

new fuel pump
new crankshaft position sensor
new spark plugs
new ignition coils
new ( well, reconditioned ) fuel injectors

and am still having very stubborn starts. after it starts it runs fine, no misfire codes, once it sits overnight / some extended time though. the hard start returns. also it seems like it may be worsening.

any thoughts?

[Cybersombosis]

Coolant temp sensor? Also have you scanned for codes? If so post them up here.

[promet]

coolant temp sensor has also been recently replaced, along with a new coolant flange.

the only code i have is ' P0441 Evaporative Emission Control System Incorrect Purge Flow ' which
i believe is the charcoal cannister or purge pump is ' filled ' and or failed. i hadn't thought that'd be a ' hard start ' vector, but now that things are narrowing down...

[Akabetterthanu]

The fuel might be draining back to the tank if your new pump doesn’t have a built in check valve


Sent from my iPhone using Audizine Forum

[promet]

i believe i had the proper model of fuel pump installed for this audi ( b6 a4 1.8t ), so i wouldn't assume that was the issue, but i'm open to the idea if that is a common thing.

i mean, why would it not have a check valve?

[EuroxS4]

I would put a gauge on the end of the fuel rail and check the pressure in the morning. It is possible injectors are leaking down.

[promet]

i am beginning to think this as well ( injectors ). i ordered a little fuel line and a fuel rated check valve, which i'm going to add between the hard fuel line and the rail. if this fails to keep pressure, can pretty well assume i guess, that the injectors are dumping. so much for refurb injectors huh? lol!

was at one point suspicious that the, though new, fuel filter ( fuel pressure regulator is integrated into the filter in the model ) was bad. odds are probably better that injectors leaking, and seems like leaking bad...

thanks guys for the feedback!

[promet]

an update on this.

installed the fuel check valve, which went well, and let it sit overnight. tried priming the fuel rail a few times by turning the ignition to on/off/on a few times. unfortunately this didn't seem to effect the hard start issue at all.

so, i proceeded to install new injectors that same day, and got a rough but somewhat improved start. let it sit overnight. and while she doesn't start on the first try ( almost ) the start situation has noticeably improved ( quick catch on the second or third crank, as opposed to a slow catch on the 5th or 6th crank).

i would of course like to have a ' snappy ' start on the first crank. so i am looking for suggestions of other causes. i have a single persistent code that i have never had go away since i've had the vehicle, which is ' P0444: Evaporative Emission System Purge Control Valve Circuit Open '

( which if you want more detail on that, i had an earlier post re: that here https://www.audizine.com/forum/showt...ve-Replacement )

but i am beginning to wonder if it really is my charcoal canister (CC) and or leak detection pump (LDP) that are somehow interrupting my fuel flow making it hard to start.

someone had suggested that a weakening head gasket may also be a potential issue, but i'd like to try to tackle the only code being thrown as the culprit first. i was originally ' ignoring ' this as i didn't think it otherwise crucial, and would be a ' last line ' fix, but it seems i could be wrong about that...

anyone have any thoughts/experience with CC and or LDP actually interfering with engine turnover? some kind of ' vapor flow ' effect perhaps?

happy to hear all thoughts.

best

[Cybersombosis]

I’d do a compression test if you suspect a weakening head gasket. We have a car that has low compression on cylinders 2 and 3 and it has a super lazy start but fires late after a few turns of the engine. Not the snappy start I’m used to.

[promet]

That seems like a valuable clue. I should probably do this on ' general principles ' anyway, lol...

thanks for the reply and your time.

[BumblebVR6]

I had a Bosch 040 pump that had a failed check valve and even w/ that, it would always start on the second or late first try.

[EuroxS4]

Fuel pressure check on fuel feed line will tell you if its a fuel supply issue or not. However with a new pump I don't see that being a issue unless its installed incorrectly or the fuel filter lines are mixed up. I have seen them cause a hard start concerns.

[promet]

thanks for that info.

[promet]

you know i did replace the fuel filter myself and i * think * i got the lines right, lol. i marked them before i removed the old filter and installed the new one.

[Turbo510]

I had a Bosch 040 pump that had a failed check valve and even w/ that, it would always start on the second or late first try.

I've never bought the fuel pump check-valve excuse for a hard start. The purpose of that valve, in my opinion, is only to keep the line full after the pump shuts off. After changing the fuel filter, or having the injectors removed, the system pressure is obviously zero. The engine has always fired right up for me.

[promet]

Quick Update:

so i mentioned in the OP, that i had replaced the spark plugs. at the time i had asked the guys at autozone, and also the mechanic who works on my a4 b6 1.8t, when it's something i can't/don't want to do myself, about gapping plugs. they both said, don't worry about it, modern plugs are pre gapped.

well my starting issue was getting progressively worse, so i moved on to ordering a new PRV valve ( back of the block crankcase pressure regulation valve - the ' pancake-looking ' one near the firewall ), which is being shipped but, in the meantime i thought, let me try some new plugs as well.

while at the autozone, i picked up four cheap plugs and a bladed gapping tool. i pulled out the previous plugs ( maybe 6 months old ) which weren't actually in terrible shape ( a little beige-colored fouling an a little oily ), i checked the gaps and they were, like 0.050 lol...

i gapped the new cheapos to 0.032, as i'd heard is ' factory ' for my model ( closer, probably to 0.030, as my gauge skips from 0.030 to 0.035 ), put them in there, and the car now starts right up, and also has significantly less lag in active acceleration, lol!

kinda disappointed that the auto parts store and my mechanic were so ' lax ' in their thinking on this, ' faulty lore '. but glad to have made progress here. also, it's made me a sort of plug gapping zealot, lol. i'm going to try my damnedest not to say anything rude next time i'm at the shop...

also, incidentally, the new PRV valve has not arrived yet, but while inspecting the old one i noticed that there was no clamp on the horizontal tube, i fastened a new hose clamp there as well, and while i'm pretty sure it's bad (the current valve itself ), i'm also sure that untightened tube hasn't been helping; just thought i'd point that out as well... i hope to get even further efficiency, and power improvement when the new valve arrives and is installed.

Here's to significant, but very cheap, wins!

DOUBLE CHECK THE GAPS ON YOUR PLUGS! lol...

[Puddin Tane]

kinda disappointed that the auto parts store and my mechanic were so ' lax ' in their thinking on this...

In my experience auto parts clerks tend to not give a rat's, over-simplify, spout bullshit, and trust those damn computers too much. They were right, though: the exact right plugs for your car should come custom gapped. Which implies those problem plugs were incorrect.

[Turbo510]

... i checked the gaps and they were, like 0.050 lol....i gapped the new cheapos to 0.032, as i'd heard is ' factory ' for my model ( closer, probably to 0.030, as my gauge skips from 0.030 to 0.035 ), put them in there, and the car now starts right up, and also has significantly less lag in active acceleration, lol! Here's to significant, but very cheap, wins!

Maybe you've (partially) solved the starting problem, but the fact that closing the gaps .020" makes it start, suggests to me that the coil Voltage may be low. The battery Voltage usually goes lower during a cold start, due to a cold battery and more viscous oil. I'd still check the coil packs have a solid and clean ground connection, also the power to those coils must have minimal resistance.

[promet]

i think part of the ' not giving a rats ' includes not offering you the ' exact right plugs for your car ', lol. regardless, i've learned something useful...

[promet]

Maybe you've (partially) solved the starting problem, but the fact that closing the gaps .020" makes it start, suggests to me that the coil Voltage may be low. The battery Voltage usually goes lower during a cold start, due to a cold battery and more viscous oil. I'd still check the coil packs have a solid and clean ground connection, also the power to those coils must have minimal resistance.

that's a very good observation, noted... i do plan to check that out... thanks.

[EuroxS4]

Check for cracked head, are you loosing coolant without any external leaks??

[promet]

I am loosing a little coolant, but I have a small radiator leak. this engine previously had very serious coolant leaks - lower coolant hose, turbo coolant hose, and a couple of other things - which have been fixed. So a coolant leak due to a cracked head wouldn't be my first thought, but... noted... thanks for the suggestion.

is there another way to check for a cracked head other than a ' non-external ' coolant leak?

[old guy]

Run a block gas test. That was how I confirmed my cracked head. I was losing a small amount of coolant weekly with no sign of an external leak.

[Cybersombosis]

Do a compression test and report back your numbers. Make sure to remove all spark plugs as there may be gas escaping into another cylinder and you will hear it by way of a whistling sound.

[EuroxS4]

If you have a cracked head you will notice 1 piston will be nice and clean due to steam cleaning action courtesy of the cracked head. The most common I have seen cyl#2 crack.

[promet]

Run a block gas test. That was how I confirmed my cracked head. I was losing a small amount of coolant weekly with no sign of an external leak.

i've ' heard rumor ' of this test, but haven't looked into it. i will take a look at how that works...

[promet]

Do a compression test and report back your numbers. Make sure to remove all spark plugs as there may be gas escaping into another cylinder and you will hear it by way of a whistling sound.

i am considering this as well, thanks for the reply.

[promet]

If you have a cracked head you will notice 1 piston will be nice and clean due to steam cleaning action courtesy of the cracked head. The most common I have seen cyl#2 crack.

i am a ' class 1 rookie ' ( to my credit, i was a ' class 5 rookie ' mechanic when i started this journey, lol ) mechanic, with no garage, so i am hoping not have to remove the head on this engine myself, lol! at least not until i've gained the confidence to do so. but i just watched a youtube video that described, and showed exactly this, which was very cool.

this car only cost me 1550usd, so i am trying not to have too expensive of a ' romance ' with it. a gasket replacement - the gaskets are cheap, but the labor even around here, i'd bet would be 1200usd or more. not saying i wouldn't do it, but... i might try a ' head sealer in a can ' first.

i am developing a little ' crush ' on the car though, so maybe i'll go ' whole hog ' as well.

primarily though, it's been running surprisingly well ( this recent quick starting plug fix, good power, and pretty smooth given its age and probably a good amount of ' previous owner hot-rod-abuse ', lol , reasonable mpg ) and, after reaching this milestone, i am just going to drive it for a little bit before making any big decisions.

I will be looking into some of these ' diagnostics ' you guys have suggested though.

speaking of which, what do you guys think about this ( ' Chemical ' Head Leak Test )?

this would of course in our case be done via the coolant reservoir, but you get the point...

" How to Tell if Your Head Gasket is Blown "

https://youtu.be/QA7KVQq9vKA

thanks again guys!