98 Express runs rough with Rotton Egg Smell

Hi guys,

I have a 98 Express 3500 1 ton with the Vortec 350. The van has 420,000 miles and it started running really bad the other day and given the rotten egg smell coming from the exaust I assumed that the Catalitic Converter gave up the gost, but after crawling underneath the van I discovered that the damn thing has two converters and the lead off pipe on the right side has another can type device and I have no clue what that is. To make matters worse there are two sensors in each exaust pipe just behind the converters. My origional thought was to replace the converter/converters with striaght pipes, but I have no idea what will happen if I leave those to sensors uninstalled and unplugged.

Thanks in advance for any advice


Wayne Mann

Hi guys,

I have a 98 Express 3500 1 ton with the Vortec 350. The van has 420,000 miles and it started running really bad the other day and given the rotten egg smell coming from the exaust I assumed that the Catalitic Converter gave up the gost, but after crawling underneath the van I discovered that the damn thing has two converters and the lead off pipe on the right side has another can type device and I have no clue what that is. To make matters worse there are two sensors in each exaust pipe just behind the converters. My origional thought was to replace the converter/converters with striaght pipes, but I have no idea what will happen if I leave those to sensors uninstalled and unplugged.

Thanks in advance for any advice

Wayne Mann

It is illegal to remove cats.
Is the check engine light on or blinking?
First thing.
Check for codes and post back codes.

Hi MT-2500,

I got derailed with work and was unable to work on the van until last week. Here is an update on my progress. First the van is not throwing any codes nor is the check engine light on. I pulled the lead off pipes off and put some more lead off pipes on from a junk yard with cats on. I tested the fuel pressure and it is right at 60 PSI at idle. I pulled the spark plugs out, they had about 15,000 miles on them and they all showed a lean condition as the ceramic insulator was a very light tan colour and the rest of the plug was just supper clean. Typically when I change out plugs in this thing the ceramic part of the plug is dark brown and the plug in general is sorta sutty black looking. I purchased a new muliti meter so that I could test the MAF sensor and a vacuum pump to test the MAP sensor, both checked out fine. I put new plugs, wires, distributor cap and rotor button in and this thing still stinks like rotten eggs and runs terrible. It has a very noticable skip especially when you put it in gear and try to pull away. The road we live on is probably on a 3 to 5% grade and the van will almost not make enough power to get up the hill. The van had been filled up with gas the last time gas was put in before this started and it was at about a 1/4 tank when everything went to hell in a hand basket. I even went and put ten gallons in with no effect. I can't find any broken or loose vacuum hoses.

At this point I am thinking it has to be something computer related. Something maybe that controls the fuel injection. Any ideas?

Thanks for the help


Wayne Mann

Hi MT-2500,

I got derailed with work and was unable to work on the van until last week. Here is an update on my progress. First the van is not throwing any codes nor is the check engine light on. I pulled the lead off pipes off and put some more lead off pipes on from a junk yard with cats on. I tested the fuel pressure and it is right at 60 PSI at idle. I pulled the spark plugs out, they had about 15,000 miles on them and they all showed a lean condition as the ceramic insulator was a very light tan colour and the rest of the plug was just supper clean. Typically when I change out plugs in this thing the ceramic part of the plug is dark brown and the plug in general is sorta sutty black looking. I purchased a new muliti meter so that I could test the MAF sensor and a vacuum pump to test the MAP sensor, both checked out fine. I put new plugs, wires, distributor cap and rotor button in and this thing still stinks like rotten eggs and runs terrible. It has a very noticable skip especially when you put it in gear and try to pull away. The road we live on is probably on a 3 to 5% grade and the van will almost not make enough power to get up the hill. The van had been filled up with gas the last time gas was put in before this started and it was at about a 1/4 tank when everything went to hell in a hand basket. I even went and put ten gallons in with no effect. I can't find any broken or loose vacuum hoses.

At this point I am thinking it has to be something computer related. Something maybe that controls the fuel injection. Any ideas?

Thanks for the help


Wayne Mann

You are welcome.
Glad to help.

What engine?

Your fuel pressure may be low for a 5.7 V8.
Should be 60/66 lbs.
Hook up the gage and do a running on the road test after pump has run and hot.
Post back key on fuel pressure and engine idle pressure and running on road pressures.

If shiping or missing when put in gear you have a cylinder missing.
I would work on that end first first.
Pull plug wires one at a time and see if all cylinders are firing good.

Other things to check is cat back pressure.

Camshaft read reading?

What is engine idle vacuum and engine at 2K rpm readings?

Hi MT-2500,

It is the 5.7 liter. I used one of the old plug wires with one of the old plugs and plugged that wire into each distributor port and tested each one to make sure that each cylinder was firing. The skipping doesn't change much as you unhook each plug wire until you unhook the wires from either of the two rear cyclinders, then it really runs bad.

A friend suggested that with 420,000 miles the cam chain may have jumped a tooth, that would be assuming a lot of chain stretching and tooth wear on the sprockets. I can't imagine that the engine would even run if it jumped a tooth.

I will get a vacuum guage and run some more checks.

Thanks


Wayne Mann

Hi MT-2500,

It is the 5.7 liter. I used one of the old plug wires with one of the old plugs and plugged that wire into each distributor port and tested each one to make sure that each cylinder was firing. The skipping doesn't change much as you unhook each plug wire until you unhook the wires from either of the two rear cyclinders, then it really runs bad.

A friend suggested that with 420,000 miles the cam chain may have jumped a tooth, that would be assuming a lot of chain stretching and tooth wear on the sprockets. I can't imagine that the engine would even run if it jumped a tooth.

I will get a vacuum guage and run some more checks.

Thanks


Wayne Mann

To check for cylinder miss remove the plug wire from spark one wire at a time.
With plug wire off at plug you can also check spark threw plug wire.

Check camshaft retart and dist cap and rotor real close.
And run a comperssion test.
Post back compression readings for each cylinder.

Hi MT-2500,

Problem solved. I though my brother had already changed out the distributor cap and rotor button. I installed the new cap and button today and the skip and horrible running condition is gone. I will put the old cap and button back in the first of the week just to confirm. These were not AC Delco parts that I had put in the van the last time I did a tune up. We have been dealing with a slight skip or miss for quite some time. I will be interest to see if that is gone as well. Upon inspection now for the second time (once when I changed out the plugs and wires) I can not see any defects in the old cap or button.

Thanks for the help


Wayne Mann

You are welcome.
You can not always tell it is bad by looking.
If it is running good after the cap and rotor repacement I wold just drop the old one in trash can.
Watch the plastic ears on dist changing caps.
They can strip out and or break.

Thanks for posting back how it went.