Misfiring during Idling and Driving

[Razi]

Background information:A few weeks ago my car's low oil pressure light glowed dim and then went off and kept doing that, but my Autometer gauge read 40 psi but it still had me worried, so I took it home and I checked the oil and it had mixed with coolant, so I started taking it apart to replace the headgasket.

During the procedure I removed and blocked off the EGR and replaced all the vacuum hoses around the intake manifold.

Also, before changing the headgasket, my vacuum at idle was at 23 but now it is at 18.

When the car starts, the low oil pressure light comes on, or it does not, it seems random.I know that once the oil pressure light comes on, the engine is probably screwed, but the Autometer gauge said things were normal that night.Perhaps it was coincidence that the oil pressure light started acting up the same night the oil and coolant mixed, I'm not sure.I have new oil in the engine and the Autometer gauge reads as normal, but the oil pressure light goes on and off randomly but I do not hear any engine knock.I will replace the oil pressure sensor tomorrow and see if the light still comes on. If it does, I'm guessing I need a new oil pump and probably new bearings.

I need some guidance.

And now, onto the misfiring problem.

The problem:Everything went together well and the car starts right up, but after a few seconds of idling, the engine starts having trouble idling and stumbles.

If I go for a drive, the engine will hesitate when I start moving, and at a stop the idle drops to around 500rpm unless I blip the throttle a few times.

Things I have done so far:-Did a boost leak test and fixed the leaks.-Fuel filter sock came off the Walbro fuel pump once, the sock is secure now and the fuel filter was a bit stuffy so that was replaced.-Injector o-rings have been checked, and they are fine.-MAF sensor voltage is around .91 volts while idling. (Checked with consult cable and laptop)-TPS voltage is around .48 volts while idling. (Also checked with consult program)-The distributor, and everything on the distributor has been replaced a few weeks ago.-New knock sensor-New spark plug wires-New water temp sensor (For the gauge cluster, so I doubt that matters)-New O2 sensor-IACV has been cleaned few weeks ago.-All vacuum hoses have been replaced-New Deatschwerks 370cc injectors-Compression test : 180psi on all 4 cylinders.

Thanks for reading through this long post!

Modified by Razi at 11:38 PM 9/1/2009

Modified by Razi at 11:46 PM 9/1/2009
Modified by Razi at 8:14 PM 9/4/2009

[trackslut240]

how about the water temp sensor for ecu? u prolly did, plug gap and timing. any way of checking fuel pressure? just somethings on my mind, i am sure u have gone thru them. i kinda have a feeling its in limp mode, hesitates and idle drops, altho limp mode idle should go up.(my s13 does that, limp mode, low idle and running at low power. cel is onor sometimes even off with limp mode )

these symptoms seem like what i had an issue with on my car. check fuel pressure and also tune. mine was tuned for 540cc but the injectors were 610, ran rich a few times but otherwise stock. idles barely, drops, bucks and shuts off.

[Razi]

I'm thinking that could be a suspect...With a bad ECU coolant temp sensor, the ecu runs too rich right?

I'm also going to test the fuel pressure this week to see if the fuel pump and things are working properly.

[trackslut240]

bad CTS(coolant temp sensor) is like a hidden gremlin, it will do funny stuff to a good running car, the lock on my cts is broken and while driving it came off, took me straight to limp mode, misfiring and all the funny stuff.u r turbo right? check your plug gaps and maybe try regapping them to .032 or something. smaller gap than stock. how r u tuning this animal? from rereading it looks like u are in limp mode. can u rev past 2000?good luck and let us know what it was.

[Razi]

Yes, the car is turbocharged and yes I can rev past 2k.The Consult program shows my coolant temp sensor reading similar temps as my Autometer water temp gauge so I don't think it is the CTS.

I'm going to check the fuel pressure tomorrow and double and triple check all my vacuum lines.

If it's still acting up, I'll change the CTS and see if that solves it.

Thanks for helping me think through some of this guys.

[trackslut240]

compression test??

[Chris28]

Check the wiring for your knock sensor. I'm sure you've checked for codes with the Consult cable, but if you're getting code 34 it's usually not the KS, it's the wiring. That could cause stumbling during acceleration.

[Runt]

Bad fuel pressure regulator? R

[Razi]

Bad fuel pressure regulator? R

Fuel pressure has been tested, 41 psi at idle.

compression test??

I'll post the results once I do them tomorrow afternoon.

Check the wiring for your knock sensor. I'm sure you've checked for codes with the Consult cable, but if you're getting code 34 it's usually not the KS, it's the wiring. That could cause stumbling during acceleration.

Do I just test continuity on the wiring?

[Chris28]

Yeah, there is a huge write-up on zilvia or fresh alloy or some other 240 site that talks about it. Usually it breaks in the part of the wiring harness that goes next to the fuel rail. I'm gonna look for the thread I was reading, it had a ton of useful info in it.

[Chris28]

Ok, WD might get mad at me for offsite linking (Zilvia lol) so I don't know what to do.

There is a thread on Zilvia called "vtec effect in a ka?" Search for that and post number 14 is by UNISA JECS. He posts a bunch of links that are extremely helpful in diagnosing the knock sensor. That whole thread is a really good read, I read it and all the threads linked in that thread like 5242364million times while trying to fix my bogging issue.

[Razi]

Nice, I found the thread.Thanks yo!

[Razi]

I'll post the results once I do them tomorrow afternoon.

I got the results, 180 psi across all 4 cylinders in the compression test.

[Chris28]

Nice, I found the thread.Thanks yo!

No problem broseph.

Compression is fine, I think it's something electrical. Maybe do the ignition mod and see if it helps at all? Definitely check up on the code 34 deal, seems like a good lead.

[Razi]

Good call on the ignition, I checked spark a few hours ago and it was inconsistent.

Blue and bright one second, and dull and weak the next.

Definitely need to check that out, along with code 34.

[Razi]

Okay, update.Probably the final update...

I checked all my injectors and the o-ring for injector #1 was torn so I replaced that and it helped my problem a lot.

Then I got curious and removed my air filter from my intake box and viola, purrs like a kitten.

I think I need to figure out a way to keep my chopped up air box and still get good air flow into my engine.

Hard to see in this picture, but if you look to the bottom right you can see an OEM looking intake box.

I cut the bottom off of an Altima or Sentra intake box so I can get it to fit and have things look like stock.

I may have to reconsider, or maybe a K&N filter will help?
Modified by Razi at 1:42 AM 9/6/2009

[Chris28]

Hmm, maybe stick a K&N inside the "stock" box? Or just have the cover for the box so it looks stock, but all it is is a cover for the cone filter?

Glad you got it all figured out.

[Razi]

Yep, that is one of the ideas I'm playing around with in my head right now.

Thanks Chris, you also helped me think out loud in this thread and gave me some good suggestions. KA-T!!

Here is an updated picture of the engine bay.
Modified by Razi at 1:42 AM 9/6/2009