Stalling upon deacceleration, sometimes.

[drew4justice]

Hi guys. A noob to the forum here.
I've done extensive research, but can't seem to find and answer, so I thought I'd post here in hopes to tap some wisdom.
What I have is a 1996 Buick Roadsmasher with an LT1. I just turned 40,000 miles last month.
I don't have much data yet, because this isssue is just starting to occur but I'll do my best.
Saturday 11/10, when approaching a red light I noticed my car stalled. I can't recall if I was at a complete stand-still or if I was still rolling a bit, but I usually let of the gas quite early and ease into the brakes. I started the car up with no issue or hesitation.

Sunday 11/11, I made it a couple miles from my house. I was approaching railroad tracks, so I eased off the accelerator and rolled over the tracks. When I made it to the other side of the tracks, I noticed the car stalled. This time it was quite difficult to start. The engine turned over quite well but simply wouldnt start. I tried about 8 times. I popped the hood and looked for the coil to see if I was getting spark. It was dark, and I'm not used to the LT1. The Roadsmasher has a giant baffle on it, so I didn't try very hard to find the coil. I decided to try to start it again and it fired up, so I shut the hood, turned around and headed back home.
I made it almost back home when I was approaching a stop sign. It died again, but started up no problem.

So, the issue appears to happen during deacceleration. After it happened, I gave it WOT and didn't notice any loss of power.

Any thoughts are appreciated. EGR valve? Maybe TPS? I know it's not much info to go on, but it's worth a post.

[shoebox]

Could be a sticking EGR valve.

[drew4justice]

That's what I was thinking... isn't there a way to test it? Like an "EGR delete" or something? I think I see guys doing that.... but then I also believe they state that it will throw a code. And, if that's the case, in turn shouldn't I be getting a code if my valve is bad?

[shoebox]

If the valve is sometimes sticking open, you could cap off the vacuum supply to the valve and take it for a drive and see if it still stalls. Of course, this assumes that the valve is closed (and it cannot be opened by the vacuum, since it is not connected).

You can always use a vacuum tester to see if the valve moves in and out freely and/or remove it and check/clean the orifices.

EGR operation codes are a little finicky and sometimes are sporadic to set.

[drew4justice]

Thanks for your curteous feedback.

I have an Amazon credit card, where I gather points for purchases. I found that I had enough points to almost fully purchase a replacement EGR valve, costing me only $4.55 out of pocket. I went ahead and ordered a valve.

I'll keep you posted.

[shoebox]

Well, it may not be the valve at all. It's just a possibility. You still have to troubleshoot before replacing stuff. If it is the valve and due to sticking, you will still likely have to do some cleaning of the orifices in the back of the intake manifold.

[drew4justice]

You were correct, it wasnt the egr valve. I replaced it and got brave because it was acting cool... Ended up having a flatbed haul it home... Was doing about 55 and felt it hiccup... Kept going about 5 miles and it just died. Started up, headed home then it died and wouldnt run... Well, it would run but idled as if i had an extreme performace cam... Had it towed home and had to leave in another vehicle for a couple hours. When i got back home i tried and it started right up, i reversed and pulled up in my driveway, then it died. I tested priming by turning the ignition key a few times, then starting.... It wouldn't start... On attempt 14, it started and ran as if nothing were wrong... Idled and revved fine... I let it idle, then it petered out and died. I gave up and went in.
I will start by checking fuel pressure, hopefully tomorrow... Then its on to spark..
Not sure whats causing this irradic goofiness.

[philosophico]

Its either fuel or spark, the fact that it just cuts off points to the ICM to me. However, check your fuel pressure first.

I been trying to track down my own problem and just found out it was the FPR. I replaced it today and it runs great, but I had other issue to which had me unsure.

[drew4justice]

So, last night.. I found an extremely small leak where the "baffle", used to resude intake noise, wasn't 100% sealed to the intake tube (far lack of better term). This is AFTER the MAF, so I thought... wow! That's it... so, I snugged it up and sure enough, it ran great.. up and down the street, around the block... hammered the throttle--no issues. I went to bed happily... I woke up and had to run to the grocery, and guess what? hard time starting.... finally started... decided to let it idle up to operating temp... went inside, came out about 5-10 mins later and it wasn't running. It wasn't even warm. UGH!!!! I have ordered a fuel pressure gauge, but it wont be here until next week... If I can rule out the fuel, I'll start looking at the ECM, TPS, OPTI, etc... the frustrating thing is that I only have 40,000 miles on this vehicle!!

[drew4justice]

I think I found an issue..
Although the fuel pump has been quiet, I can't seem to hear it any longer.
I rented a fuel pressure gauge from AutoZone and connected to the schrader on the fuel rail at the back of the engine near the EGR valve.
Before, while, and after cranking, I saw no change on the gauge. It read 0 PSI.
I disconneted the electrical connector between the bumper and the gas tank--it is a 3 prong adapter with 3 wires, purple, grey and black. I probed between the black and the grey with one of those light bulb diagnostic probes.
Every time I turned the key to the on position, the light lit up for about 5 seconds. It also stayed illuminated while I cranked the motor.
I'm guessing the problem is either with the connection at the pump, or the pump itself. I won't know until I drop the tank, if I decide to....
I just had the pump replaced with an AC delco unit about 4 weeks ago.
This is very disappointing...

[DUDBIRD113]

I know that the fuel pumps can fail shortly after installing it. Acdelco is a hit or miss on some of there products due to them outsourcing some of the parts they make.

[shoebox]

You should have mentioned the recent work on the pump. It takes the thread in a whole new direction. Something could have gone wrong with the install, connector or hose may have come off at the pump. People don't always get things right in there. It also seems odd that you would have replaced the fuel pump, but did not have a pressure tester already.

When you turn the key to ON, the pump primes, then shuts off. That is why you see the test light on for a few seconds.

[drew4justice]

Sorry, I should have mentioned the fuel pump replacement.
I realize the 5 second light is for priming, I just wanted to communicate that the prime function appears to energize.

I tried quite a few times to build pressure on the fuel line yesterday with no luck.
With the gauge still in place, I decided to try before leaving for work. I primed the system and heard the pump! I glanced at the gauge, and sure enough it was loafing at 35psi. The engine started right up. I did nothing other than let it set over night.
While it was running, I reached underneath the car and tugged/wiggled the 3 wires and the 3 prong adapter, but it didn't have an effect. I couldn't get it to stall.

Thanks for everyone's feedback. This is driving me bananas.