The dreaded flashing Check Engine Light

[Motojoe86]

Your fuel rail should read fuel pressure, not vacuum. It's been a while, this motor has a cam right? If so, then that vacuum reading isn't too low, just a little less than a stock cam which would be 20-21.

An intake is a lot less expensive and time consuming than some of the other repairs!

Im sorry, I meant to say fuel trim. I have to re read through these posts lol. I think someone said that far negative fuel trim meant vacuum leak maybe?

 

[afpj]

negative fuel trims indicate running rich IIRC, so that ECU is trying to hold back fuel. Typically an intake leak causes positive FT because the ECU detects lean condition and trying to ADD (positive) fuel. Can you see a graph on how your O2 sensors are behaving?

 

[Motojoe86]

negative fuel trims indicate running rich IIRC, so that ECU is trying to hold back fuel. Typically an intake leak causes positive FT because the ECU detects lean condition and trying to ADD (positive) fuel. Can you see a graph on how your O2 sensors are behaving?

As it turns out, im a complete idiot lol. I was reading wrong dial. It actually was positive 25 fuel trim. I noticed when I rev it up, fuel trim comes back into range. I believe thats inline with a vacuum leak? Im still learning the nuances of this app. I'll try to find o2 info. Thanks!

 

[Scottydoggs]

if thats the long term fuel trim pegged at +25 thats a large vac leak.

 

[Motojoe86]

if thats the long term fuel trim pegged at +25 thats a large vac leak.

Would that likely be intake manifold? I know its not scientific but I sprayed all around engine a few times with carb cleaner and never got an idle change. I think I am in over my head

 

[Scottydoggs]

it could be a busted plastic vac line too. so spray them all down too, around the tb and injectors where they seat under the rail.

or maybe the leaking manifold port is under the intake. harder to spray under there for sure.

 

[FinalBreath05]

Following, have this issue to a "T"

 

[Motojoe86]

I finally got it fixed. It turned out to be 2 separate issues. My intake was bad (shocker). I had no immediate nor obvious telltale signs. Carb cleaner didnt raise idle. Smoke test didn't habe discernible smoke coming out. Changed the intake gasket anyway to see. It immediately stopped the cold start problem and trims came back within range. Still had blinking cel on highway though. Fuel pump didnt have smooth arcs at 20 milliseconds (likely worn brushes). Changed fuel pump and now it runs like a champ. Better gas mileage, smooth idle, no cel and much more responsive. Unfortunately it looks as though my delay cost me my cats though. Voltage is haywire on bank 2 sensor. That'll be next purchase. Long story short though, the cold idle problem and trims were my intake gasket. Flashing cel was my fuel pump

Following, have this issue to a "T"

 

[Merc1973]

Mine did the flashing CEL thing when it sucked up a bunch of steam through my bad intake gaskets in the car wash. Rough as hell idle couldn't d get it above 2500 rpm, cleared up when the doors opened to the car wash and i drove it out in the dry air. Hope it helps. Just changed my intake gasket yesterday and went through the car wash, no probs.

 

[Sean Hennessy]

I guess I'll keep this going.
2002 Tahoe, 84000 miles.
P0300 code flashing light on highway and, with the truck in park, from 1600 rpms to 3000. After 3000 rpms the misfire goes away.
Fuel trim totals are well under 10%
Vacuum gauge reads 20 in. with a steady needle.
Fuel pressure for flexfuel 5.3 sits at 42 psi and same under load.
Fuel injector balance test was good.
Had the crank relearn done, free by a friend.
New fuel pump/filter over a year ago, pump went out on me.
And plugs and wires.
Fuel regulator tested by pulling off vaccum line, no leaking fuel and the fuel pressure went up.
Cleaned throttle body and MAF sensor.

Truck runs fine, power is good, you can feel the mis at idle, sounds fine in the 2500 rpm when its really misses.

Cyl. 5 is the only one with 0 misfire.
Cyl. 2 has 1500 and Cyl. 3 has 1200. Which are the highest. Swapped coils with Cyl. 5 and 2, still mis on Cyl. 2.
All other Cyl. Have under 100 misses.
So need to do a compression test just to make sure all is good, but running out of tests, and limited by my $5 Torque Pro app scan tool.