99 suburban hard start

1st post.. 2 ?'s..

4x4 5.7l w/80K miles..engine is hard to start in the morning after sitting overnight..after first start of day all is okay..i tested pressure, and drop was very slow after engine off..should pressure be maintained in fuel system overnight?..have been thinking press reg but maybe leaking injector? they're both next to each other, but how hard are they to get to? could another type of reg be cut into return line? i changed fuel pump 3 mos ago after original fp failed..the hard start is getting to my wife.. :banghead:

i found oil in coolant..a friend suggested that oil cooler in rad could be problem..i have a new rad, upper/lower hose and a gallon of simple green max to help flush...any tips on the rad change out...from the top it looks fairly straightforward..

thanks for any tips,
william

What does the pressure do after shutting the engine off for 5 minutes? 15 minutes? 30 minutes? It should not drop to zero. What is the fuel pressure while the engine is cranking when it is hard to start?

Has the intake manifold gaskets ever been replaced?

//2000CAYukon

i have only done a 5 min test as suggested in my Haynes manual..drop was within acceptable specs according to the book.i will perform the other tests to find out..

intake manifold gaskets have never been changed..

thank you for the reply..i'll post back with results..
william

After you get the engine started from a hard start episode, how does the engine run? Like normal? Coughing, missing, rough? The GM manual states fuel pressure should be 55-60 psi, it used to state acceptable drop values, but now only stated not below 55 psi. The injection system in that truck need alot of fuel pressure to open the injectors, if you have less than 55 psi the manual states you could have a lean condition, hard start cold, no start. Hope this helps.

after the first start of the morning the engine will start and run fine(smooth with plenty of power) for the rest of the day..during the hard start it cranks and the engine sputters for several seconds until it begins to run..

i tried something different this morning..while cranking i held the gas to the floor, thinking more air through the throttle body might help..it seemed to make things worse(cranking without even the sputtering)...i let off the gas pedal and the usual starting symptoms came back..

on edit: i also changed the coil, cap, rotor,wires, and spark plugs about a month and a half ago..hard start problem started just before changing these parts out and new parts had no result..

Holding down the pedal all the way is known as "flood clear mode". It will actually do the opposite as you were hoping to do. It will keep the injectors from opening, thats why the condition came back when you let the pedal up. The injectors started firing. Double check the fuel pressures, and post back.

i performed pressure tests at test port with Actron 0-100psi FP gauge..

hooked up gauge this morning..it seemed there was no pressure after sitting overnight..

with key on/engine off pump ran and pressure up to 62 psi.
after pump shut off 60psi..

engine started(almost a normal start event, not the usual hard starting :disappoin ) and pressure while engine running 52 psi..

engine shut off and pressure 55 psi..

after 5 mins there was a slow, steady drop to 40 psi...

after 15 mins pressure was 35 psi..

after 30 mins pressure was still 35 psi...

key turned on and 62 psi with pump running..engine started fine..engine shut off and 59 psi after pump shut off..after 5 more minutes the pressure was still 59 psi...:banghead:

i'd really like to make sure this is an injector or regulator problem before i pull the upper intake manifold off(there's a bunch o stuff on the top to get through)..

thank you for any tips or advice...tomorrow morning i am doing the cooling system flush and radiator R/R in hopes my oil in coolant problem is solved..:uhoh:

william

Well, I definately think you have a leak somewhere. I don't suspect an injector, just because they are individual injectors, and the chances of more than one going bad is slim to none. It sounds like either a fuel pump or a regulator leaking down. Here is how I determined which is leaking. Under the driver side of the truck the fuel lines go from metal on the frame to plastic, jumping over to the transmission, then they go back to metal. There are 2 possibly 3 plastic lines there. One line is the pressure line to the injectors (largest diameter, and comes from fuel filter), one is the return line, one is the vapor line (part of the evap. system). I don't remember what the return line and vapor line look like to tell the difference, but if you follow them forward and back from the connections (metal to plastic), I think it is possible to tell which is which. Take a pair of vice grips and pinch the return and pressure lines plastic part of the fuel line after you get the fuel pressure as high as you can.
Since the regulator only drains to the return line, it will not be able to return to the tank, and if your fuel pressure bleeds down you should find the regulator leaking. If the pressure doesn't drain, remove the clamp from the pressure line and see if it starts to drain, if so, the check valve in the pump is leaking down. I know you said it is a new fuel pump, but Mr. Webster puts the definition of new and good on different pages.

Now for the disclaimer: Even though I have done this test many many times, I still am nervous about clamping a plastic fuel line with a pair of vice grips. I have NEVER has one break or fail, but I just get nervous when the clamp locks on the pliers. It is an easy and fast way to diagnose a fuel pressure leak down, but I just want you to know I have done it successully. Hope this helps. Post back your results.

thank you for the quick replys klinn..that is an excellent tip on isolating the regulator and fuel pump..my Haynes manual recommended cutting a shut off valve into the return line, but i'd rather not cut into it if i don't have too..

i hope if it is the valve in the fuel pump my wife doesn't have 34 gallons of gas in the tank like she did when it failed the first time.. :bloated: that sucked..

will post back results,
william

well, even if you find the fuel pump bad, you can drain the tank. Just go around and borrow all the neighbors lawn gas cans. That truck has the wiring harness where you can easily activate the fuel pump and use it to pump the fuel out (if it is bad, it might not hold pressure, but it can still pump fuel.) I can walk you through that if it comes to it.

I think you mentioned something about oil in the coolant. Make sure you flush out the cooling system extensively. I'm not quite sure what affects the oil has on the cooling system, but it needs to be seriously flushed out. At our dealership we had a Duramax engine heat exchanger fail, and same ending, oil in the coolant. We used a Dawn and water mixture for 5 complete flushed before we put in the coolant and water mixture. The Duramax cooling system is about 2x as large as yours, but I would think there would be a need to make sure you flush it out multiple times. I think we ended up going through 3-4 gallons of dawn, then countless numbers of straight water to flush out the dawn. It is quite time consuming, but worth it.

hey klinn,

thanks again..i spent all day on the cooling system..i do believe i got 98% of the oil out..like i said, i spent all day flushing everything out...everything went okay until...

it was me against the 10 cent o-ring for the heater core supply hose quick connect fitting..after all was put back together, running and heated up , i noticed a small leak there..waited for the motor to cool a little..found the o-ring had a rip in it..of course i had nothing in my garage and everything at the local parts store was almost what i needed.. i jammed a few things together(2 new o-rings of the wrong size and a rubber grommet to be exact :screwy: ) and it should hold for a week or so until i find an old style nipple for the intake manifold..then i' ll put in a little piece of hose to connect the line....

little stuff like that must drive you professionals crazy.

i will address the fuel pressure problem during the week(or when my back stops hurtin from leaning over that motor all day)..

i'm an electrician by trade..if you ever need any help in my field, i hope i'm the first you ask...you have my sincerest thanks..:)

william

The coolant quick connect you are talking about came apart. The oring is suppose to be in the piece on the engine, not on the heater inlet hose. You can buy a new quick connect at the dealer parts, they are dependable, but come apart as you found out. Not sure if you can get them at a local auto parts store, but might be worth a try. Be gentle when you remove it, they are known for breaking off in the intake. It happens so much, the tool trucks that come to the dealership have developed an extraction tool for the piece that is left in the intake after they break. I own a couple of them. I don't have any reason not to trust the quick connect and would use them instead of replacing the nipple with an old school nipple and then trying to adapt the hoses. Just my preference. Last time I checked, the quick connect was about $10. I would like to have seen the way you repaired that connection. I have seen all kinds of interesting patch type repairs in my time at the dealer. Some are really ingenious, some are like how did they ever work.


I could have used your services last week. The light pole in the front of the house didn't work and after trouble shooting the photo cell, found out it was a break in the underground wire. I can do that kind of work, but I don't like to dig. 75' of wire later and blistered hands later the light works.

klinn,

i would have gladly helped you..but for me to do the digging, you'd have to work on my 04 Ford Excursion with 03 6.0 powerstroke..that's how much i like digging...by the time you got that truck running right, i'd have dug a hole to China.. :grinyes:

hey klinn,

just to clarify..that last post i made was certainly NOT a knock on your abilities..it was a statement about my other truck..it has been in the shop 3 times in past 6 weeks for engine problems..

this morning i started on my first vacation in 3 years..i got 150 miles away from home(which ended up being in the middle of nowhere) in my Excursion and the rear end started making some noise..i limped it back home with my trailer and took it to the dealer for repair..

after i left the ford dealer i stopped at the chevy dealer for the quick connect fitting..i found a deep 1 1/4" socket which fit perfectly on the fitting..a little pressure and SNAP...broken in the intake manifold...i did end up getting it out after an hour...the new one went in fine..doesn't seem to leak..you called that one right on..

i'm writing this because after reading my other post, i thought it may have been able to be misunderstood..forums like this only work if people are willing to share information..the fact that you are a pro and take your time to help a stranger/amateur says alot about your character..

glad you got your light fixed..it's easy, except for the digging..

thanks,
william