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Old 07-19-2021, 04:08 PM   #21
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Originally Posted by gabedrummin View Post

Smells like gas. Plug has maybe 2k on it.
So do they all smell like gas???
what is your fuel mileage???

I need a little info
you say the car idles at around 700 RPM if you accelerate slowly everything is fine.
If you accelerate quickly it bogs until around 1500 RPM then smooths out.

So here is what I need to know: is this while driving or parked in neutral???

Also what happens if you go wide open throttle from 1500???? does it accelerate normally or???

My thoughts are, well actually more of a guess, is that you have one or more injectors that are leaking.
The bog when trying to accelerate from idle quickly "could be" from to rich of a mixture from a leaking injector or injectors.

Once your at 1500RPM the engine is starting to breath getting more air and it is bringing the rich mixture more inline. So the engine smooths out.
If the car will accelerate more normally from 1500 to wide open throttle that would kind of go alone with injectors leaking because the engine is demanding all the fuel it can get under those conditions. And being a little rich is what it needs under those conditions.

If the car bogs when you try to go from 1500 to wide open throttle then we have another issue like not enough fuel.

But I need the above info and a vacuum test and maybe another test or two to rule out some things, like poor cam or valve timing, vacuum leaks, to low or to high of fuel pressure, air metering- measuring issues...
Hope this all make some sense....


Last edited by blue62; 07-19-2021 at 05:41 PM.
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Old 07-20-2021, 03:24 AM   #22
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I connected the durametric and it shows cylinder 4 with misfire's . I do have to admit I don't know what I'm looking at . I'm not a professional mechanic and I don't understand what I am seeing when using the durametrics software .There is a box for each cylinder .I put a check in each box at the left for each cylinder ,on the right side of the page is a box and for each cylinder and for cylinder 4 I see the number counting up .So I assume there is a problem with cylinder 4 . I don't think I used my words right to explain the problem . When I try to accelerate the engine runs choppy its not revving cleanly .What I said was a bog is the engine not having that snappy response when you hit the gas . I hit the pedal fast the motor cant rev fast because its back fires thru the intake as the engine rpm increase and once it gets above 2 thousand rpm I don't notice it running bad .When I press the gas slowly the motor has time to accelerate . And I don't hear backfires. So I guess you are all right its either a bad injector or I have a dead cylinder . I guess I could change the coil pack to another cylinder But I doubt the miss fire will follow the coil .I don't think its timing or it should show one or both banks with a problem ? Porsche dealer had said multiple cylinders were misfiring but I don't see that . I see one. If this was a fuel pump problem I think all cylinders should have an issue .When I had the heads off the car all the cylinders looked great no scuffing no scoring a nice even colored wall . I have been a tool maker for 35 years and understand making parts and the walls were not worn . I so do appreciate all your help and patience helping me .Thank you all

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Old 07-20-2021, 05:20 AM   #23
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if you want we can do a zoom some time and I can show you some things to look at with durametric and then we can post some screenshots of the results.
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Old 07-20-2021, 05:38 AM   #24
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Originally Posted by gabedrummin View Post
I connected the durametric and it shows cylinder 4 with misfire's . I do have to admit I don't know what I'm looking at . I'm not a professional mechanic and I don't understand what I am seeing when using the durametrics software .There is a box for each cylinder .I put a check in each box at the left for each cylinder ,on the right side of the page is a box and for each cylinder and for cylinder 4 I see the number counting up .So I assume there is a problem with cylinder 4 . I don't think I used my words right to explain the problem . When I try to accelerate the engine runs choppy its not revving cleanly .What I said was a bog is the engine not having that snappy response when you hit the gas . I hit the pedal fast the motor cant rev fast because its back fires thru the intake as the engine rpm increase and once it gets above 2 thousand rpm I don't notice it running bad .When I press the gas slowly the motor has time to accelerate . And I don't hear backfires. So I guess you are all right its either a bad injector or I have a dead cylinder . I guess I could change the coil pack to another cylinder But I doubt the miss fire will follow the coil .I don't think its timing or it should show one or both banks with a problem ? Porsche dealer had said multiple cylinders were misfiring but I don't see that . I see one. If this was a fuel pump problem I think all cylinders should have an issue .When I had the heads off the car all the cylinders looked great no scuffing no scoring a nice even colored wall . I have been a tool maker for 35 years and understand making parts and the walls were not worn . I so do appreciate all your help and patience helping me .Thank you all
A backfire thru the intake can only happen from:
Bad ignition timing
Bad intake valve timing
intake valve sticking open
collapsed intake lifter
weak or broken intake spring
something that allows the burning fuel/air to leak past an intake valve.
Something that prevents the intake valve from sealing properly at the correct time during the combustion of the fuel/air mixture.
any one of these things could cause a misfire.
If you have backfires into the intake you have one or more intake valves not fully sealing or not sealing at the correct time.
A vacuum test should show a ticking needle every time that cyl. comes on the intake stroke.
If you have multiple valves out of time or not sealing you will have low vacuum possibly with a steady needle or possibly with a drifting or ticking needle.
A compression test should also show lower compression for that cyl. or cyls if the intake valve-valves are not sealing or are out of time.

So at this point I think a vacuum test and a compression test on all cylinders is very important to try and pin down your issues.

Until we know that you have proper vacuum which relates to proper compression, we are going to chase our tails.
When a cylinder does not fill properly with the fuel/air mixture at the correct time,or burn at the correct time it can look like many many other issues.
I think cylinder 4 misfires are caused by an intake valve issue the fuel air/mixture is not burning correctly leading to the raw gas smell.
Which is leading us to think you have injector problems.
Is cylinder 4 one of the plugs that smell like gas??????

So you could have more then one issue.
Intake valve issues on at least number 4 cyl. and possibly fuel injector issues.

Last edited by blue62; 07-20-2021 at 08:29 AM.
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Old 07-20-2021, 03:32 PM   #25
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I'm not well versed with the timing issues so I'll pass to blue one that one. I can talk for days about the injector leaks though. Our oem injectors are prone to sticking open. It's happened to several members. You will smell gas in your crank case when you open the oil fill tube and if you change your oil it will run out like water. This most often will happen after the car sits for a while. Piwis software (and durametric I think) allows you to turn off individual injectors to try to troubleshoot some issues but there's no great way to tell if an injector is leaking except for pulling them and testing. Testing is a process best done by reputable shops but it's not cheap. What is cheap is to retrofit 986.2 Bosch injectors - you'll pay less for them new than you will to have the old ones recalibrated. While timing issues will cause intake backfires, a leaking injector will not. I agree that it sounds as though you may have more than one problem. I would check your oil. If it reeks of gas and is thin as water you can at least start to nail down one issue.

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Old 07-20-2021, 04:04 PM   #26
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After getting more information from the OP in post #22 where he describes how the car reacts to throttle. And also the fact that it is backfiring into the intake.
Here is what I think is happening.

There is some issue with at least one cylinders valves.
OP names #4 cylinder.
There is some issue with the intake valve. it is not sealing at the seat.
Due to something like a broken spring. a weak spring. a collapsed lifter.
A sunken or damage valve seat. Something is preventing that valve from sealing properly.
The only way a backfire can happen in the intake is for burning fuel to get past the intake valve.
So I think there is an intake valve issue.

If there is a valve issue the fuel/air mixture is not burning properly in that cylinder.
So exhaust from that cylinder is rich in oxygen.
So when the exhaust from that cylinder get to the O2 sensor the O2 sensor sees only the oxygen. that's all it reads. So O2 sensor voltage goes low.
The DME/ECU sees this as a lean condition and adds fuel.
Now you have a very rich condition on that cylinder.
If there is a valve issue with more then one cylinder the same thing is going to happen.
The more misfires the more fuel is added by the DME/ECU

IF I am correct then the spark plug on #4 cylinder will smell of gas.
Or any cylinder that is misfiring
This is also why the OP smells fuel on start up.
Most of his misfires are at 1500 RPM or below
Also if a compression test is done #4 cylinder it will show lower compression then the other cylinders.

Now having said (typed) all this I could be wrong.
But I can only think of one way to get a backfire into the intake.
"Intake valve issue"

OP may also have injector issues. (Leaking)

Last edited by blue62; 07-20-2021 at 04:15 PM.
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Old 07-21-2021, 05:11 PM   #27
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I will try to get my hands on some test equipment this week end , and report back the findings .Both heads had a valve job less than 2 thousand miles ago by Hoffman machine . But anything is possible . My idea was to swap injector from 4 to 5 to see if the problem follows the injector .Thank you for all your comments . You are all extremely knowledgeable and I am great full for the help..!
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Old 07-21-2021, 06:52 PM   #28
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I will try to get my hands on some test equipment this week end , and report back the findings .Both heads had a valve job less than 2 thousand miles ago by Hoffman machine . But anything is possible . My idea was to swap injector from 4 to 5 to see if the problem follows the injector .Thank you for all your comments . You are all extremely knowledgeable and I am great full for the help..!
If I am correct with my guess that the issue is in the valves you will probably be able to see the affects the easiest with a compression test of all cylinders.
Any cylinder with valve issues will show a lower compression.

If you do a vacuum test your looking for 18-22 in.hg with a rock solid needle. like it is painted on the gauge.
If the needle quivers or ticks or drifts that points to valve train issues.

When you do the compression test:
Be sure to pull the fuel injector fuse
Block the throttle body butterfly wide open
crank the engine the same amount of time for each cylinder.
Record compression on each cylinder.

Let us know how you go.
Always interested in outcomes

It will be grand if it is just a leaking injector
Easy fix

Last edited by blue62; 07-21-2021 at 07:10 PM.
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Old 07-24-2021, 10:55 AM   #29
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So vacuum test shows 21 Hg of vacuum , needle is not moving even when revving the engine needle dose not move .
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Old 07-24-2021, 01:38 PM   #30
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So vacuum test shows 21 Hg of vacuum , needle is not moving even when revving the engine needle dose not move .
Your pulling good vacuum so it does not look like you have any vacuum issues.
Steady needle is good
When you do a snap throttle test the needle should drop to near zero then rebound a little above your idle vacuum then settle at idle vacuum.

Here is a site that you can go to and read up on vacuum testing.
It will be better that a back and forth here on the forum.

what-when-how.com/automobile/engine-vacuum-test

That article should help you out some.
sounds like your valve train is ok but do further vacuum tests (described in the article) to prove that out.
A compression test would remove any doubt.

If it is not a mechanical issue (valve train) I would start looking at fueling.
Fuel pressure and volume tests and also the injectors for leaks.

keep us in the loop
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Old 07-24-2021, 05:41 PM   #31
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Compression test shows cylinder 4,5,6 at 150 psi and 1,160 2 ,155 3 ,150 I used two different gauges and still got a difference of about 10 psi from bank 1 to 2 I also ran the car with cylinder 4 coil unplugged and it still backfire . Very confusing results . Bank one plugs looked black color where as bank 2 the insulators are cleaner .

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Old 07-24-2021, 06:11 PM   #32
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Just to make sure you are numbering them correctly (have done this myself).

Post #9:
https://rennlist.com/forums/boxster-and-boxster-s-986-forum/568600-cylinder-number-layout.html

so:
1: 160
2: 155
3: 150
4: 150
5: 150
6: 150

Did you do this with the engine hot or cold?

I'm paying close attention to this one in case your fix is what I need to do for mine.
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Old 07-24-2021, 06:47 PM   #33
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cold engine throttle wide open injector fuse pulled 3 second crank.
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Old 07-24-2021, 07:48 PM   #34
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Compression test shows cylinder 4,5,6 at 150 psi and 1,160 2 ,155 3 ,150 I used two different gauges and still got a difference of about 10 psi from bank 1 to 2 I also ran the car with cylinder 4 coil unplugged and it still backfire . Very confusing results . Bank one plugs looked black color where as bank 2 the insulators are cleaner .
So your vacuum test is good.
10 psi difference as the greatest spread is ok.
So I think you valve train is good.
Blows my valve leaking theory all to hell thou.

Are all three plugs from bank 1 blackish???
Blackish plugs are either oil fouled or very rich fuel/air mixture.
Or not firing every time.
So you have to figure out if they look oil fouled or not burning well because of a to rich mixture.

What kind of fuel mileage do you get.????

I would get a spark tester the kind you put between the coil pack and the spark plug so you can test current to the plugs on bank 1

there is a chance your coil packs are not getting energized.
If so that would be a wiring issue.
If that checks out ok then I would look at the injectors.
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Old Yesterday, 06:57 AM   #35
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Believe it was #3 where it was mentioned there were misfires so blackish plugs would make sense in that aspect. What is causing the misfires though I think is the issue.

Can't remember, but did you try swapping coils from bank 1 to bank 2 to see if the misfires follow?

Offer to do a zoom to look through duramtric still stands. With a cold engine here is what I would capture:
rpm
oil temp
misfire cylinder 1-6

Do it with a cold engine, let it get up to temp, then export to a CSV file and link to it here.

What I noticed at one point with mine is that misfires would happen once the SAE turns off and then rpm's would fluctuate. the data from durametric is easy enough to graph out in Excel too so putting charts to things can help visualize things.
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Old Yesterday, 08:11 AM   #36
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Believe it was #3 where it was mentioned there were misfires so blackish plugs would make sense in that aspect. What is causing the misfires though I think is the issue.

Can't remember, but did you try swapping coils from bank 1 to bank 2 to see if the misfires follow?

Offer to do a zoom to look through duramtric still stands. With a cold engine here is what I would capture:
rpm
oil temp
misfire cylinder 1-6

Do it with a cold engine, let it get up to temp, then export to a CSV file and link to it here.

What I noticed at one point with mine is that misfires would happen once the SAE turns off and then rpm's would fluctuate. the data from durametric is easy enough to graph out in Excel too so putting charts to things can help visualize things.
Swapping coils from one bank to the other can only tell you if the coil is good or not.
There is nothing wrong with doing that as a test.
It tells you if the coil is good or not.
But it is an incomplete test.
The coil and spark plug needs to be tested on the head = cylinder that has the misfires. A coil and or spark plug will not fire if the wiring to the coil or plug is faulty no matter how good the coil or plug is
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Old Yesterday, 09:04 AM   #37
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https://www.youtube.com/watch?v=T70D3jJ_CfA This is the vacuum test I did today with a hot motor and a very long vacuum line . Way different from yesterdays results ? Guess I should of done this on a hot motor . Coils have been moved from bank 1 to 2 the plugs from cylinder 6 to 4 . Miss remains on 4 .The dark plugs are from bank 1 the whiter ones from bank 2 .The miss is on bank 2 . I don't see how you can change injectors in the car? Maybe on bank 1 but with the air cleaner in the way on bank 2 I don't think so. I have another set of heads on the motor with low oil pressure I guess I have to start saving some money to get the heads re-done pull the motor replace the injectors with the motor out. I wish Porsche could tell me its your head or injectors . They made no mention of a bad valve only needing coils and injectors . I don't trust the dealer . I feel like after spending 2200 they would say I need to spend more money ,if it still showed a miss .I got charged 904.00 dollars to change out a mass-air flow sensor .The simplest thing possible .It made no difference and they had the audacity to say it runs better.When it runs the same no change at all .You all are the best thank you so much for all your help .Thank you.
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Old Yesterday, 09:26 AM   #38
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ok, now I am really paying attention. Your vac is worse then mine.
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Old Yesterday, 10:25 AM   #39
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First: where are you attaching your vacuum line?
You want it after the throttle body

Second: real long hoses between the vacuum gauge and the intake can affect readings.

Third: do the test with engine cold and engine fully warmed up.
that way if you have a vacuum issue that is only present when cold or hot you have a better chance of seeing it.

fourth: When you do the test start by just letting the engine idle steadily.
Just watch the gauge for 2-3 minutes at idle. watch for needle action if any and note the reading.
ideally you want a rock steady needle. at 18-22 in.hg

Fifth: do a snap throttle test: from Idle go wide open throttle and quickly release the throttle. Needle should very quickly drop to near 0 then rebound to a little over idle vacuum reading then settle at idle reading.
Let the engine idle again for a few minutes and see if readings vary from the first idle session.

The dark plugs appear to be oil fouled or a very rich fuel mixture.

You have replaced your coils more then once so they are most likely good.
Don't switch them around. If there is a misfire issue related to coils or plugs your just moving the problem around.
We want to pin the problem down.
Test them in place under running conditions. Use a spark tester that goes between the plug and coil. they light up every time the coil fires the plug.
Or use a digital volt meter.
or do it old school by pulling the plug hook it to the coil then lay it on the head and crank the motor look and see i the plug sparks.

If you are positive that you have misfires on bank 2 then we need to concentrate on bank 2
Test the coils on bank 2 in place on bank 2 that way we know if the wiring to the coils is good or not.

The oddest thing to me about your problem is: if you are having misfires but you have no CEL or codes something is not right with the DME/ECU or the wiring.
Or something is not hooked up right when the engine was replaced.
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Old Yesterday, 12:50 PM   #40
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For your earlier question about replacing bank 2 injectors.

It is possible to do it with the airbox there. It is a pain. What is the biggest issue is the lower AOS hose that goes from the AOS to the front of bank 2. It snakes around the intake. Pulled the intake out once and dont really want to do it again cause it's just a roayal pain.

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