Outer Limits 4x4 Board

Hi guys

I have a G16B 16 valve MPFI engine in my Sierra

Has been running sweet for years.

I recently went for a wheel when suddenly the engine wouldn't produce power under load. I manged to limp the car home but since then I haven't been unable to fix the issue. I have had some talented people help me too but still cant put our finger on it.

The engine code is still spitting out 12 which means normal start.

I have put in new plugs, the leads are only 2 years old and look in good condition.

It won't start with the MAS plugged in and the car will idle without it but still produce no power under load. If I put the MAS on after starting it seems to run worse than without it. I have checked for air leaks and don't believe there is any. I have changed the MAS with one from the wreckers, no change. All other sensors seem not to be lose.

Help me Obi-Wan Kenobi your my only hope

Thanks In Advance
HR

EDIT: I checked the fuel pump output by eye (no gauge) and it seems to be a steady flow with good pressure.

Been in any water anywhere?

Have u by any chance swapped the MAS and or ecu with a known good working one?

as wouldnt be the first dodgy wrecker part ive heard of.

I am pressuming it is getting spark ok at idle as its idling ok but maybe loosing spark under load.

Have you checked the ignition timing? Maybe jumped a tooth on the cam belt, or flogged out the crank pulley key?

Ben

i agree with ben, check the bottom pulley first. also check the pcv valve. this is the little emissions thing that feeds some air back into the intake, and it may be playing up. if you are getting a code 12 than i would look for mechanical, rather than efi problems. also make sure the dizzy has no white corrosion covering the hall effect sensor etc.

BenT wrote:Have you checked the ignition timing? Maybe jumped a tooth on the cam belt, or flogged out the crank pulley key?

Ben

X2 on this one, look for any red dust around the bottom of the timing cover or the harmonic ballancer, this indicate's that something has come loose

Do you have to remove the battery to reset limp mode and to reset codes from the ECU?

HRZOOK wrote:Do you have to remove the battery to reset limp mode and to reset codes from the ECU?

yes, or just pull the main fuse for a few seconds. if you are only getting a code 12 than the ecu will not be in limp mode.

No water nicbeer I steer clear of mud and water.

Yeah I was thinking I could have another dodgy MAS

If ya live in Newy and have the old skool MAS (pod/Cone style) on ya zook bring it round to test and I will fix ya up with some beers....Serious

compression test

I pulled off the TPS and still got code 12 from ECU so I guess we can discount the fact that it is giving code 12.

It idles OK without MAS but after connecting runs worse and if the accelerator is jabbed quickly it tries to stall.

I guess it wouldn't be a mechanical issue if it idles OK without MAS?

BenT wrote: Maybe jumped a tooth on the cam belt,
Ben

I have seen em do this I had a 1.3 in a sierra towed in to work sounded like no compression but cam was turning pulled the front cover of to find the belt had jumped teeth about 7 or 8 camt really remember, but if it only jumped 1 or 2 could do what your saying I would check there first

hope this helps

jimbo jones wrote:

BenT wrote: Maybe jumped a tooth on the cam belt,
Ben

I have seen em do this I had a 1.3 in a sierra towed in to work sounded like no compression but cam was turning pulled the front cover of to find the belt had jumped teeth about 7 or 8 camt really remember, but if it only jumped 1 or 2 could do what your saying I would check there first

hope this helps

Would this show the timing being out if I used a timing light?

HRZOOK wrote:

jimbo jones wrote:

BenT wrote: Maybe jumped a tooth on the cam belt,
Ben

I have seen em do this I had a 1.3 in a sierra towed in to work sounded like no compression but cam was turning pulled the front cover of to find the belt had jumped teeth about 7 or 8 camt really remember, but if it only jumped 1 or 2 could do what your saying I would check there first

hope this helps

Would this show the timing being out if I used a timing light?

yes, but for an accurate reading you must have the diagnosis plug shorted out, as if you were checking codes.

joeblow wrote:yes, but for an accurate reading you must have the diagnosis plug shorted out, as if you were checking codes.

On a side note any reason why I am only getting code 12 from ECU. I am guessing if it is blinking I haven't shorted it out incorrectly?

Sounds like a cracked inlet manifold.

Spray round the inlet manifold with some carby cleaner. See if the idle picks up. I was going to do the front mount in the subaru this weekend, but it looks like i will have to put that off. Let me know if you want a hand.

Layto....

also check your fuel pressure regulator. mine went really gutless wen i put a different fuel reg on. but it could have died.

To check for a mechanical fault such as the timing belt jumping a tooth simply use a vacuum gauge and make sure it has full manifold vacuum where you "T" it in........

It should be around 21 inhg at idle and if it is much lower then say 18 then you either have a big vacuum leak (easy to diagnose) or a valve timing of similar issue.

me217 wrote:also check your fuel pressure regulator. mine went really gutless wen i put a different fuel reg on. but it could have died.

Where is this located?
Thanks
HR

HRZOOK wrote:

me217 wrote:also check your fuel pressure regulator. mine went really gutless wen i put a different fuel reg on. but it could have died.

Where is this located?
Thanks
HR

I checked this quickly the other day. Its the correct reg and it has no leaks.

Layto....

lay80n wrote:

HRZOOK wrote:

me217 wrote:also check your fuel pressure regulator. mine went really gutless wen i put a different fuel reg on. but it could have died.

Where is this located?
Thanks
HR

I checked this quickly the other day. Its the correct reg and it has no leaks.

Layto....

You da man Homer

OK after much dicking around and changing many a part I should have stuck to my original thought....the fuel pump

Pressure tested the pump and it was producing a massive 10 PSI.

I guess I am pulling the tank out tomorrow

Whats the fuel pressure supposed to be?

HRZOOK wrote:OK after much dicking around and changing many a part I should have stuck to my original thought....the fuel pump

Pressure tested the pump and it was producing a massive 10 PSI.

I guess I am pulling the tank out tomorrow

when i'm doing my " by the eye ball " fuel delivery check, i take the return line off so if it has a steady flow you know it has at least reg pressure behind it.

islandvitara wrote:Whats the fuel pressure supposed to be?

I think about 35 PSI but someone else might clarify

^^^Sounds about right.

Layto....

maybe fuel fiter is blocked

Nah, it has a new fuel filter on it

Layto....

Also I tested before the filter and after the filter

you really need to look at fuel pressure. and air fuel mix in the exhaust. low fuel pressure will produce exactly this.