Home Forums Gear Hunting Trucks and Four-Wheel Drives 1999 Suburban mechanical puzzler

5.7 engine won't start unless accelerator is fully depressed, dies if you let rpms get low. If you can keep it running for a couple of minutes (2 to 3k rpm) you can get it into gear at about 1k and it drives semi-normal, then eventually it will idle in park at 1k or so.
If you shut it off, it starts the same problem all over.
The shop can't take it until Tuesday.
Background 160,000 miles and did a 180 mile highway trip without incident the day before this happened. Started normal that morning, then drove to a strip mall. After sitting for 30 minutes the trouble began.
Any ideas besides injector or pump?
The truck has been nearly trouble free for 16 years.

My '98 has a lot of trouble with distributor caps. When they go it starts hard and it has very little acceleration. Think I've put 3 on it in 3-4 years. When I first got it, it could be pretty temperamental when it rained really hard too. Why I changed the cap the first time.

They are notorious for that problem, especially if they sit a lot.

Thanks, changed the cap a year ago, but this is different.

Try having your vehicle OBDII codes read at an Autozone or NAPA. If you have an Android phone or pad, you can download Torque Pro app and buy an OBDII reader off Amazon and read your own codes. Total cost for both is less than $30.

Once you have your codes, do a search for them on internet for an exact solution to your problem.

Fuel filter?
Bad fuel on the R/T?




I bet a can of seafoam fixes it.

Fuel pressure regulator?

Fuel pump filter screen is clogged. Drop the tank and clean it.

You bought bad gas from some one.

There could be such a thing as PassLock on your Suburban. You might have a "security" light lit on the dash. If so, the procedure is as follows:

Turn on ignition for 10 minutes.
Shut off and wait 20 seconds.
Turn on ignition for 10 minutes.
Shut off and wait 20 seconds.
Turn on ignition for 10 minutes.
Shut off and wait 20 seconds.

Start engine.

These trucks have fuel pump problems. I'd run it with a fuel pressure gauge hooked up. Run it down the road and watch the gauge. It should be in the 55 to 65 psi range when at cruising speed. At idle, it will drop to around 45 psi. I know you said, "not pump". So my question is how do you know it is not the pump? I'd also check the fuel pressure regulator. Also make sure you don't have any vacuum leaks. I'm sure if you are having drivability issues, you are probably getting a check engine light. What codes is it showing? When was the last time you checked the cap and rotor????

Lots of good ideas.

BSA Didn't say not the pump. I listed it with injectors as a possibility. Pump and pressure regulator remain a possibility.

Walt Reading the code is cheating. But I'll do it if I can drive it safely.
At the closest parts store where they run the test for free, a guy asked to borrow the reader and they never saw him again. They don't have one any more.

Mike Fuel was fresh before the highway trip from a high volume Quik Trip. No problem until the next day''s second trip. Sea Foam was administered early on and if I can keep it running long enough to get enough through, it has potential. Fuel filter was changed about 40K ago.

Micky Dropping a tank with 30+ gallons of fuel in it is not for me. We'll see.

pal It cranks and runs okay at high RPM. If that changes I'll try the procedure.

I'll mess with it again tomorrow and see what happens. I appreciate all the input.

Someone'll be dropping the tank and installing a new fuel pump.

Pretty sure it has PassLock.

It wouldn't be the first one for that year of suburban. It damn sure won't be the last either... One of my friends has a '99 and has changed the fuel pump 5 times since new. Thank god I have never touched mine!!!!!!!! I have had rough running, backfiring, stumbling/missing, lean air fuel problems. So I know what the OP is going thru.... These things are also notorious for going thru distributor caps if you don't buy the right one. Even if yours is newer (a year old), don't rule that out as a possibility. Only buy AC Delco (factory OEM) OR an Accell and they will last a long time. I just replaced my original equipment cap last year. However, I learned the hard way and went with a store brand distributor cap and it gradually ran worse and worse. It took me a while to figure out it was the fairly new cap that was the problem. If you pull yours, blow the inside of the distributor out with a light compressed air because small fragments of aluminum or brass may be causing problems inside the distributor, hence arcing out and causing misfires... Like I said before, test the fuel pump pressure while it is under load. If it checks out, you'll know your pump is good. If you can get the codes, let us know what they are and we can possibly be of more assistance... No I am not a mechanic, but I know my way around most vehicles ... Good luck with it..

99 Suburban part deux.

I only had a minute today so I just tried to start it normally. Fired right up and idled right down. I think it's messing with me. Next step...codes.

It couldn't just be the Sea Foam that fixed it, could it? It was still seriously messed up just yesterday. Regardless, I don't trust it yet.

Give your head a shake! That stuff is PFM!



And stay away from ethanol.

I'd still look at the fuel filter. 40K miles could stand a replacement.

Mass air flow sensor? Mine threw a code so I bought a replacement sensor and when I opened it up, there was a bird feather on the screen. Now tell me how a bird feather ends up between the clean side of the air filter and the MAFS sensor? Let me tell you, low paid dealer lube techs that just go through the motions of upselling you filters you don't need and not paying enough attention to what they're doing.

How about the throttle position sensor? I've had a couple go bad and also had some I've fixed by taking the connectors and unplugging and plugging them in several times to make sure the connection isn't compromised.

Just a couple of thoughts.

Clean the throttle body.
(throttle plate / butterfly )

Went to take it in today, went crazy on the way. Limped back to change trucks as I had other things to do. Thinking distributor cap is part of a bigger problem.