99SuburbanTX

This is my wife's truck and it has begun behaving strangely. Twice it has stalled out on her while turning through an intersection. This is coming gently off idle when it occurs. The last time she noted that the gauges all lost power and the voltmeter dropped into the red zone (low volts) just as the engine died.

I took the truck to the local auto parts store to have the battery and alternator tested. Battery was good (only 2 months old) but the positive terminal was loose. The alternator was only putting out 45 amps at 2000 rpm (should be 105 amps). So, I bought a brand new alternator and made a conversion from the side mount to the top post mount on the positive terminal.

Today we were driving along. I came around a gentle corner and then into a straight section. After gently accelerating away from the corner (~.25 mi) the engine suddenly died. It started up immediately. While watching the volt gauge inside the truck the volts are hovering around 12.5V to 13V instead of the the steady 14V it used to be.

I am going through the chassis grounds near the engine, but I am looking for some other ideas to chase down.

kevinkpk

The alternator will only put out what it needs to maintain proper voltage, you should understand that it is capable of 105 amps.
In regards to the low voltage output, I'd suggest verify the dash voltmeter is correct. If it is low, that indicates to me either loose belt, or faulty voltage regulator which is in the alternator.
If the guages go out then engine dies, look as you are for grounds, and loose anything. If nothing, I'd then suggest get some non conductive electrical spray cleaner. Inspect all the fuses especially the ign fuse, remove one at a time with key off, and clean the pins, reinstall ect. Thats clean the pins on both the fuse, and terminal they plug into.

kevinkpk

I should add, if autozone has 105 anp available load, and the alternator voltage output started to drop at the 45 amp level, the VR in the alternator is not working as it should. I am not aware how parts stores that test alternators do that. I do however, know how they work.

99SuburbanTX

The other item I am tracking down is a potential vacuum leak. Basing this off of two other symptoms I have noticed: 1) Engine stutters a bit when cold for about 0.1 mi, then returns to normal & 2) Occasionally during hard accel the tranny seems to want to hang in 1st and doesn't upshift until the accelerator is lifted. Does anybody know where I can get a schematic of the vacuum system?

tucdon

I have a 2002 suburban 5.3 and it will start but when I give it gas it dies

99SuburbanTX

Went to the dealership service desk. They suggested the two common failures for the 5.7 are the fuel pump and fuel pressure regulator. The fuel pressure regulator can cause the engine to stall out if it floods the engine - likely during low rpm and load. Since I have also noted a decrease in fuel economy I thought this sounded likely. So, I bought a new one and a gasket kit. Suffice to say, GM's engineers did not have serviceability in mind when they created the SFI system. You need to remove the entire upper plenum to get to the fuel spider, which is where the regulator is located. So, after a long afternoon's work I finally got the engine torn down, part replaced and everything put back together.

So, I started it up and everything was great until I began to rev up the engine. It fell on its face. Anything other than very gradual throttle increases is met with misfiring and stalling. Intermittently. 8075% of the time it runs like c r a p, but then there is 20% of the time where it begins to act normally...just enough to get one's hope up and then to return to even crappier running.

Thoughts??

kevinkpk

Sounds like a gasket leaking on the manifold to me.

Kiowa Suburbanite

On the stalling with voltage drop. I have a 99 2500 with 7.4L. When I first got my Burb I test drove it around 20 miles. Even had it checked out by one of those companies that checks 74 things or something like that. Drove great. On the way home I drove down the dirt road to my place and the engine was cutting out intermittently. I got home and popped the hood and the cable was loose. So I cleaned it and put it back together. After that it would do it every once in a while. Kept a wrench in the glove box and tightened it and it was just fine. Then one day it wouldn't do anything and it was as tight as it would go. I looked at the cable real good and it had corrosion under the red plastic layer. I pulled it and replaced the cable and it fired right up. The cable is about 8ft long and I couldn't find it at any auto parts store so I had to go to the dealer. It was 76.00. I think I saw it on Rock Auto Parts though for around 30.00

The other crappy running problems is probably caused by the fuel injectors. I know a guy with the spider style injector unit and he had the same problem as you're describing. That's what it was for him.

I am having the same problem. Figured it was the fuel pump. Dropped the tank and spent 315.00 for a new Delco pump at Napa. Put in a new fuel filter, cut the old one in half and it was filthy. Ran fuel injector cleaner through it and it ran better but still wasn't up to par. Did a complete tune up which is a serious pain to get to the distributor with all the crap in the way. Still didn't cure it. Runs fine under a light load but craps out when you try to pass someone on the highway. Used to just rip right by with that 454. Put a trailer behind it and it has a real hard time. I am currently throwing all sorts of part at it. Starting with all the injectors, a head job, new fuel pressure regulator, coil and a few other things that were a pain to get to with the plenum in place.

I would try the battery cable 1st for the actual electrical shut down.

73shark

Welcome to the forum.

Might check exhaust back pressure for clogged cat.

chaparel

What does your RPM look like when you are at idle?

If you are still having problems with this you may want to check your tbi, I had simular problems with my trailblazer till it wouldn't run, it is very easy to clean.

John