Stumble on acceleration

Tiny
TI3VOOM
  • MEMBER
  • 2005 SUBARU LEGACY
  • 4 CYL
  • AWD
  • MANUAL
  • 80,000 MILES
2005 Legacy GT ~80K miles now.
I purchased the car used in 2008 Feb with ~28K miles. It had a slight miss at idle. Service shop said this is normal for Subaru's. As it was my first I accepted this.
Summer of 2010 I began to get CEL calling for Cyl 1 misfire.
I did much reading on diagnosing and solving the problem. With that, I ran a fuel injector cleaner regimen with no effect. I checked all sensors and cleaned the MAF with no effect. I then swapped coil packs between cylinders and did a compression test. Compression was ~145psi across all cylinders. With no change in CEL frequency, everything above pointed to a bad fuel injector. I then replaced all four fuel injectors. With this, the car now idles normally, purrs like a kitten at idle. But, with the fuel injector change the car now stumbles on acceleration. It ran fine, short of idle miss and CEL, prior to this. Seems to accelerate normally when cold but once warm, it stumbles on initial acceleration. The stumble is very similar to a bad accelerator pump on a carbureted engine. I've looked for a vacuum leak in the intake system with no luck.
I'm out of ideas and open to other input to bring it back to normal.
Do you
have the same problem?
Yes
No
Sunday, February 27th, 2011 AT 2:39 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
First, that isn't normal. I can't believe they said it is. One of the most common problems is a bad head gasket. However, your compression is good. I would check to see if there are any leaks from cylinder 1. Also, when you pull the #1 plug, what does it look like? Have you checked plug wires, plugs. For a tune up? Are you sure the #1 plug wire isn't arcing causing a miss? Has any tune up work been done? Once last thing. Have you checked the EGR for carbon build up?
Was this
answer
helpful?
Yes
No
Monday, February 28th, 2011 AT 3:21 AM
Tiny
TI3VOOM
  • MEMBER
I forgot to mention with my initial messsage, after replacing the fuel injector, I no longer get the CEL.
Leaks from cyclinder 1? Meaning perform a leak down test?
Plugs look good, light brown/tan dusted look. All plugs consistant. There are no plug wires. Just a coil pack on top of each spark plug. I swapped them between cyinders initially to determine if it was a coil or injector causing the problem.
All scheduled maintenance performed on schedule.
I'll check the EGR. How would the EGR, having carbon build up, have a sudden step change with the injector change?
Was this
answer
helpful?
Yes
No
Monday, February 28th, 2011 AT 10:31 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
When I said plug wires, I ment the boot. I've seen them actually arc from the boot, but if that didn't change anything. The EGR could create a vacuum leak if it isn't sealing shut. Also, yes to the leak down. If you're not getting a cel, that leads me to believe it is vacuum related or fuel pressure related. Especially with no cel light. To me that indicates there is no electrical issue. IS the fuel pressure within spec?
Was this
answer
helpful?
Yes
No
Monday, February 28th, 2011 AT 1:08 PM

Please login or register to post a reply.

Recommended Guides