1999 Suburban "Starting" issue - has fuel & spark, but will not start ...

[OverRunWithSons]

Wife here writing this up, asking for suggestions to fix our Truck, as it runs great still (at 200,000 miles) if we could just figure this out...

One day it will start up fine, the next ...it causes trouble, has spark, has fuel, will see black smoke out the tailpipe... the other day I got it started after 4 to 5 tries, it spit & sputtered, but got it to work then revved it good...as I recall the smoke looked white...

But husband & son said it was black tonight coming out tailpipe... they were doing this outside in the dark with a flash light..son saw fuel spitting out of carburetor.

Wondering if the Colder temp's could have an effect? (below 32 degrees here).. we had same issue last year this time , changed the cap & rotor/ plugs and appeared fixed... ran fine the rest of winter.. and now it's doing this again.. He bought a new cap & rotor tonight... no effect.. New Battery was put in Jan this year...

Any suggestions ??

[AussieinNC]

Are you certain this has a carb on it? As a 99...it should have fuel injection...

If it has fuel injection...it sounds like the fuel pressure regulator is bad, possibly leaking fuel into the manifold, giving you the black smoke...

White smoke is almost always brake fluid being burnt by the engine...check the brake fluid level and the boosted vacuum connection....

If it a carb, the choke plate could be sticking on too long...

Is this parked outside ?

[rpmerf]

White smoke could be coolant also. It will smell like coolant. Oil could look white. Usually a bit blue. Again, should be able to smell it. Black is unburnt fuel.

If it has been changed to carb, I would be looking at the accelerator pump, and see if the bowl is leaking out overnight. On my 70, after about 2 days of sitting, it will consistently take about 15 seconds of cranking before the bowl is full.

If it is still fuel injection, you might want to invest in a bluetooth ODBII scanner. You read the sensors with your phone to see what they read in real time. You should be able to see right away if a sensor is reading off. Run the codes. Could be something stored that wasn't serious enough to throw the CEL.

Verify the fuel pressure before starting, while cranking, while running. Need to test it while it is having trouble starting. It could be the fuel pump going out and sometimes supplying enough fuel, sometimes not.

Check the plugs.

There are many things it could be, but this should give a good start.

[OverRunWithSons]

Thank you so much for the 2 replies given.. I will copy these & give to my husband...I dont know the answers if fuel injected or Carberator off hand....yes...the Truck has been sitting outside..

I will definitely reply to what he figures out...and if /when we get this figured out... Hate to scrap this truck as when it runs..its GREAT...and very reliable ...


So a fuel pump can randomly work then?? I thought it does...or doesn't... We can hear it coming on when we start to turn key... For the times it spits & sputters struggling but wont start.

[rpmerf]

When it is going bad, it can randomly stop and start working. A wire will break and if they are touching, it works, if not, it doesn't. It can stall out, let it sit for a couple minutes, try it a couple times, and it works. Sometimes hitting the tank with a hammer can help jostle it enough it get it running again.

If you can hear it come on when you turn the key, then I believe it should be fine. Just be sure to listen so you know if it came on when it doesn't start.

[OverRunWithSons]

Husband is home today.. he is not sure how to check the FUEL PRESSURE ?? He is asking if there is a "Shrader valve" he has to hook the pressure gauge up to?

It is a Fuel injected suburban, a throttle body .

Where is this "Fuel pressure regulator " located ?

He plans to change the Fuel filter today... also we have a OBD11 scanner we can hook up to a laptop and get a reading.. will get back with whatever this reads later today I hope. It started the other day!

[OverRunWithSons]

Ok... he changed the fuel filter today... we got some codes...

PO172: ECU- 10 - Description: System too Rich

PO175: ECU -10 - Description: System too Rich

PO420 : ECU- 10 - Description: Catalyst system efficiency below Threshold

[OverRunWithSons]

More info on those codes:

A code P0172 may mean that one or more of the following has happened: (Code PO175 said the same basically)...

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters can cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak.
There could be a fuel pressure or delivery problem
Possible Solutions
Possible solutions include:

Inspect all vacuum and PCV hoses, replace if necessary
Cleanthe MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect fuel lines for cracks, leaks, or pinches
Check the fuel pressure at the fuel rail
Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)

************************************************************

P0420 is one of the more common trouble codes that we see.

This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). Catalytic converters are not normally a "wear" type item, that is they are not designed to wear out and need replacement. If they have failed, it is likely due to something else that caused it to fail. This is what a P0420 means in simplified terms.

Symptoms
The main symptom to the driver is the illumination of the MIL (malfunction indicator lamp). You will likely not notice any drivability problems, although there may be symptoms. For example, if the substance inside the catalytic converter is broken or failed, it may be restricting the exhaust which will result in a feeling of reduced power output from the vehicle.

P0420 DTC Code

Causes
A code [/p0420]P0420 may mean that one or more of the following has happened:

Leaded fuel was used where unleaded was called for (unlikely)
A damaged or failed oxygen / O2 sensor
Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
Failed or underperforming catalytic converter (likely)
Retarded spark timing
The oxygen sensors in front and behind the converter are reporting too similar of readings
Leaking fuel injector or high fuel pressure
Cylinder misfire
Oil contamination
Possible Solutions
Some suggested steps for troubleshooting and fixing a [/p0420]P0420 error code include:

Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
Inspect the downstream heated oxygen sensor, replace if necessary
Replace the catalytic converter
Diagnostic Tip
Generally speaking you can look at the temperature of the exhaust just before and just after the converter using an infrared temperature gun. The output should be about 100 degrees Fahrenheit hotter when the engine is fully warmed up.

Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (02 sensor). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

[rpmerf]

Schrader valve should be on the fuel rail. If pressure drops quickly, you might have an injector stuck open.

FPR should on the drivers side fuel rail. Look for gas in the vac line.

If you can watch sensors, watch the o2 voltage to verify the codes. Watch others such as MAP and engine temp to verify they are reading correctly.

Deal with the rich issue first. I think cats do not like running rich.

[95 S_Trucker]

This is a 99 suburban. It should be in the the 88-98 GMT400 section.

There is a schrader valve on the fuel line. Its near the distributor cap.

The fuel pressure regulator is inside the upper intake manifold.

With the codes you provided, it sounds like the fuel pressure regulator or the injector assembly is leaking. Your husband will have to remove the upper intake manifold to access them.

The P0420 will not affect how the engine starts or runs.

[OverRunWithSons]

Not sure I understand why a 1999 should be in a forum where the cut off truck year is 1998 ?

So... he changed the fuel filter ... put 2 bottles of dry gas in ...that's all so far... and it seems to be starting every day.. problem is likely NOT fixed ...and it will start acting up another day... hard to take it to someone to help us when it acts GREAT 75% of the time.. then has these starting issues so randomly... it did this last year too... when we changed the cap & rotor and plugs, it lasted the rest of winter.. all summer long it ran GREAT ... then this started again randomly...

Thanks for all your help.. it gives us more to go on.. we'll see how long this lasts.

[95 S_Trucker]

If it worked last year, try it again this year and see what happens.

88-98(GMT400) trucks look like this:



99-06(GMT800 platform) trucks look like this:



Your 99 Suburban looks like this. It's built on a GMT400 Platform.



There were some overlap years. They kept the GMT400 platform up to 2000, even though they introduced the GMT800 trucks in 99.

[duke_lbz]

I had a similar issue with my 98 Yukon. Would start and run fine most of the time but let it sit a few days and would not crank. Had same symptoms, would fire and was getting plenty of fuel. Ended changing the distributor once it finally quit and couldn't get it to start. And that has fixed my problem.

[hatzie]

Originally Posted by rpmerf

When it is going bad, it can randomly stop and start working. A wire will break and if they are touching, it works, if not, it doesn't. It can stall out, let it sit for a couple minutes, try it a couple times, and it works. Sometimes hitting the tank with a hammer can help jostle it enough it get it running again.

If you can hear it come on when you turn the key, then I believe it should be fine. Just be sure to listen so you know if it came on when it doesn't start.

Electric fuel pumps internals can wear out so that they loose the ability to build full specified pressure.
When the pump output pressure drops to the ragged bottom edge of the system pressure needed you get driveability and startup issues.

It'll show the same symptoms as a failing fuel pressure regulator. At 200,000 + miles it would not be shocking for the fuel pump to be worn out. Fuel pressure regulator the same way.

I've pulled the upper intake on a couple rigs and found the lower intake washed clean by leaking fuel from the SCPI injector lines or the fuel pressure regulator.
It it hasn't been done yet upgrading the old SCPI spider to the MPFI spider is a fairly large improvement. It's not inexpensive so you want to be sure the injector spider is the issue. Delphi is OEM GM but you really pay for it. AC Delco is not as expensive.