93 Astro Problem

[Battle Cry]

I have a 93 Astro W code. I just replaced the fuel pump. After replacement, there is a miss or hesitation at idle and a slight surgeing/backfire at cruise speeds. The speed does not matter. I do not mean cruise control. It is getting less than 10mpg currently. It has no problem accelerating other than a slight hesitation. I thought maybe it just needed ran hard to clean it out, so I ran it up to 102 mph. That didn't do it. It acts as if it is loading-up. It is not shooting a code. It ran just fine before I replaced the fuel pump. The pump is a genuine Delphi pump. I don't know the fuel pressure. It does a slight raw fuel smell. It has a heavy sulphur smell. Had the sulphur smell before I changed the fuel pump. Temp gauge shows 200 degrees on the digital dash just like normal.

Here is a list of things I think it could be:
O 2 sensor
Catalytic Convertor
Egr Valve
Air Filter
Bad or faulty fuel tank vent tube that runs to the charcoal canister
vacuum leak
anything else that anyone can think of feel free

I thought about the cap rotor plugs and wires. They were replaced 30,000 miles ago. If it was the ignition switch it wouldn't run. Remember this all happened after I replaced the fuel pump and the van went 102mph after the pump was replaced but still drinking too much fuel and running rough.

It has 341,000 miles on the original engine and transmission. Its an EXT LT and has been coast to coast.

YOUR HELP IS GREATLY APPRECIATED and THANK YOU FOR YOUR TIME,
Andy

[old_master]

All of your symptoms indicate a lean condition. Perform a fuel pressure and a leak down test, then post the results back here.

[Battle Cry]

I removed the plentum from the top of the engine and cycled the key. When I did this, the fuel pressure regulator would pour fuel out the vent hole. I went to NAPA and purchased a new pressure regulator for $44 and installed it. After I installed it, I cycled the key to check for leaks and there was no leaks. I also found a worn-out vacuum hose while disassembling the plentum and replaced it. I assembled the top side of the engine compartment and fired it up. It runs perfect.

To check the pressure regulator without taking the plentum apart. I pulled the center spark plug on the passenger side and smelled it for fuel odor. It had a fuel odor. Just to be safe, I put a new spark plug in and ran it. I then pulled out the new spark plug and smelled for fuel odor. It did have fuel odor. The fuel pressure regulator is located on that side of the engine and when the regulator is faulty the center spark plug is just below the excess fuel drain. Had the problem been a broken plastic fuel line inside the plentum, I would have pulled the center spark plug on the driver's side.

Hope this helps someone else out
Andy

[old_master]

Glad to hear you got her going again! Might be a good idea to change the oil and filter as a precautionary measure. Any time the engine runs overly rich or has an internal fuel leak such as you had, the excess (raw) fuel runs by the rings and into the crankcase, dilutes the oil, and greatly reduces the lubricating ability of the oil.

The drain holes you are referring to are in no way connected to the combustion chambers. They drain to the crankcase. The fact that you smelled fuel on the plug means nothing more than that cylinder is getting fuel. Checking fuel pressure and watching for leak down will tell you if the regulator or the lines inside the plenum are leaking.

[Battle Cry]

The two outside plugs or front and back, were not soaked with fuel like the center plug. If, what you are saying is true, then, the fuel would run straight down to the crankcase and it would not create a rich fuel environment. When fuel is leaked out of the regulator, it is then dropped into the center combustion chamber to be burned. Same goes for the opposite side of the engine, when you have a spider injector problem.

[old_master]

So you're saying the holes go to the combustion chamber of the center cylinders, what stops combustion pressure from entering the plenum when the engine is running? And why are there only two holes?

[Battle Cry]

Where else would the excess fuel go, when the pressure regulator leaks? Why would the engine start running rich and foul only the center plug? If what you are saying is true, then the more the engine is running in this condition, the excess fuel would fill the crankcase oil. The oil had no fuel odor. This information that I'm using is coming from a GM Goodwrench mechanic. This is the process that he uses to diagnose 4.3L engine problems with this particular set-up. Next time, I hope there isn't a next time, I have it apart, I will look this over more closely.

Have A Great Day
Andy

[brcidd]

The excess fuel sprays directly into the air intake path- through the intake valves when they open - or seeps through a poorly seating valve- I have actually seen a hydrolocked engine from a severe fuel leakage problem-where the plenum was puddled - and when you pull off the oil pan- I could see the fuel dripping down through the backsides of the pistons-filling the oil pan- and my face once I pulled off the pan- the piston rings don't keep all the fuel sealed in- but enough to hydrolock it...heck the starter would not turn it over

You stated you have a "W" engine in your first post- then you said you got a new regulator for $44- That W engine "spider" assembly- is nearly $300 which includes the regulator- and the regulator is not sold separately-- maybe what they sold you was the plastic pipes and line kit that attaches to the spider assembly-- that is what generally goes bad- they tend to crack at the bend in the plastic line......

[old_master]

Look at the second picture in this thread:
http://www.automotiveforums.com/vbul...d.php?t=473110

This is a CPI intake and it shows 6 large holes. Those holes go directly to the intake ports and are sealed from the plenum area, (regulator, injector and lines) with a gasket. On the driver side you can see a small drain hole, (there is one on the passenger side also, but not visible in this photo). If the regulator or lines leak, fuel is drained through those holes to the crankcase. The air in the plenum area is not used for combustion. All air used for combustion passes through the MAF sensor then enters the upper plenum section and directed to each cylinder. The GM goodwrench tech is either feeding you a line, or he doesn't understand the system.

[brcidd]

So why did mine hydrolock on fuel- when I had not seated the plastic line to the spider properly? and had a severe fuel leakage there? Once I found and fixed the leak- all was fine--I never touched the injector nozzles. I have a lower plenum stored in the barn-- I'll look at it tonight--

Also what is the difference between CPI and CMPFI? I thought all "W" engines used CMPFI...

[old_master]

The only way fuel can enter a combustion chamber is through a nozzle, past a nozzle, or through an intake manifold runner. I did some research on this and found out the drain hole passages go into the #3 and #4 intake runners. The area the fuel runs into is on the backside of the intake valve. That area is sealed from the combustion chamber when the valve is closed. If the valve is not totally sealed, the fuel will run directly into the cylinder. If enough fuel collects there, it can cause hydra lock. It’s a pretty rare occurrence though because the fuel will slowly seep past the rings and drain into the crankcase. Sorry for the incorrect information in posts 4 & 9.

GM classifies both the W and the X engines as CPI, (Central Port Injection). There are two versions: CMFI, (Central Multiport Fuel Injection) which has one injector that squirts all cylinders simultaneously in the firing order. The fuel is squirted on the backside of the intake valves and is there when the intake valve opens. The second version is CSFI, (Central Sequential Fuel Injection). This system has an injector pack with 6 mini injectors. They squirt sequentially with the firing order.

[brcidd]

Yes- I agree-- I checked the lower plenum I have in the barn- I can see the two holes that lead from the inner plenum area into the air inlet passages in front of the intake valves at number #3 and #4 as you stated--

My hydrolocked engine was the direct result of installing a used engine in my '94 Astro-- I have to pull of the upper plenum to gain enough engine hoist clearance to pull the engine out the front- I have to have the engine puller bar right against the top of the engine- minus the upper plenum-- so when I installed my used engine- my engine hoist must have disturbed the plastic lines into the spider assembly such that it leaked badly- unbeknownst to me- after I was done and trying to start this engine for the first time in this van- The starter turned about 5 seconds and bam locked into place-- I pulled the oil pan to see the dripping gas from number 4 cylinder-- I then pulled the upper plenum off- to see the big puddle of gas - and the leak at the plastic line into the spider- sure was glad to know why that engine locked up- and was such an easy fix... that used engine I got for $750 - out of a '96 blazer- had only 46,000 miles on it-- sure runs nice in my Astro......thanks for clearing this up...