2003 Suburban K1500 - Misfire on no load

My K1500 LT with 5.3L engine just started to run unevenly and cut out - it restarts eventually but runs very rough with small amounts of blue smoke when it begins to run more smothly.

It will cut out when my foot is off the gas. e.g coming up to a Stop sign or stopping in traffic.

I looked through these threads and it appears those misfires occur under big loads like going up hill or towing.

Any help or opinions appreciated

Fuel pressure?
What about the tune up end?
What mileage and service history?
Any check engine lights?
Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Yours is 55-62 lbs
Cold start should be 60-62 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 55-62 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

Thanks for the quick response.

2003 K1500 LT - 39,000 miles last oil change at 30,0000 along with fuel and air filter.

The engine is also converted to run on either Liquid Petroleum Gas (LPG Propane) or Petrol.

The uneven running is more pronounced on petrol

The engine just died while it was warm - I'd been out about 30 minutes.

I don't have access to equipment to measure all those pressures and also I live in UK on the south coast near Southampton.

The "Check Engine" lamp will flash then be continuous and then flash - the engine contiues to cut out at low revs. It restarts with a lot of cranking.

Also I noticed a small amount of blue smoke on revving teh engine till it smoothed out.

Cheers,

Thanks for the quick response.

2003 K1500 LT - 39,000 miles last oil change at 30,0000 along with fuel and air filter.

The engine is also converted to run on either Liquid Petroleum Gas (LPG Propane) or Petrol.

The uneven running is more pronounced on petrol

The engine just died while it was warm - I'd been out about 30 minutes.

I don't have access to equipment to measure all those pressures and also I live in UK on the south coast near Southampton.

The "Check Engine" lamp will flash then be continuous and then flash - the engine contiues to cut out at low revs. It restarts with a lot of cranking.

Also I noticed a small amount of blue smoke on revving teh engine till it smoothed out.

Cheers,

Not sure on the conversion.
But if it runs on the OEM injector system on reg gasoline/petrol.
It will need the fuel pressure specs I posted.
A flashing check engine light means a engine miss problem.
You will need to get some one that knows how to work on the conversion system.
Also you will need to get the codes check for the check engine light .
If you can get the codes post back code no.
Good luck MT

Thanks again - It will have to wait till Monday now.

I will go to the guy who completed teh conversion first in case there is soething obvious.

Then it means finding a local GM mechanic with the relevant test gear.

Cheers,

I have been running on petrol for over a week now - the LPG conversion was disconnected.

The engine starts fine and when warm will idle at about 500 rpm and will die on selecting reverse or full lock on sterring. With a stong smell of petrol from teh exhaust and smoke.

The suggestion from the LPG conversion engineer was thatthe DTC was showing multiple misfires and should change the plugs and that the Idle Control Valve may need replaceing or adjusting.

Where is the Idle Control Valve?

Cheers,

N.

Check that fuel pressure and work on the engine missfire.
Clean TBI and IAC valve. The IAC will be located at the intake air bypass passage. You really need a good engine scammer to test IAC valve.
Post back the code no's that was retrieved.
MT

Thanks for your advice.

It is booked in to a US Auto specialist on Thursday - I assume he has all the electronic diagnosis equipment and will focus on the right area.

Cheers,

N.