stalling, erratic idle

[70c-10]

I am having some problems passing smog (running rich) and am wondering if its related to some problems I recently had.

A while back the truck stalled twice on me on my drive home from work. I thought that it could have been b/c I was running low on gas. I made it to the gas station and filled up. When I got home I noticed that the truck was idling erratically - surging up and down. Looking under the hood, I didn't see anything obviously wrong. I thought that it might be a fuel filter. I had to drive the truck to work the next day(only vehicle) and I picked up a fuel filter on the way home. During the time driving the truck, the problem seemed to go away - it didn't stall and the surging stopped happening, so I did not replace the filter.

Another thing that I’ve also noticed is that when the truck is cold, it will stall sometimes if I immediately shift into reverse or drive after starting it up. If I let the truck run for 30-60 seconds, it doesn’t do this.

[Shyguy]

What year truck and what engine and transmission does it have?

[70c-10]

oops - sorry about that.

It is a 1988 C1500. It has a 700r4 and a 5.7L with an edelbrock MPFI system, heads, cam, headers and fuel pump.

[ChevyTech]

From your reply to this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=355812

Originally Posted by 70c-10

As the engine slows down after revving it up, I can hear a rattle/tapping that I think could be a bad lifter. The results of my smog test were 126 HC and 2.13 CO% @ 15mph, 117 HC and 1.82 CO% @ 25 mph.

It’s running rich & dirty. Does that thing stink something terrible?

Is this thing setting trouble codes?

Is it running on a stock ECM & chip?

You have headers. Are you running a heated O2 sensor?

Stock TBI systems will not tolerate much of a cam. Does it lope, at all, at idle?

[70c-10]

Originally Posted by ChevyTech

From your reply to this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=355812

It’s running rich & dirty. Does that thing stink something terrible?

Is this thing setting trouble codes?

Is it running on a stock ECM & chip?

You have headers. Are you running a heated O2 sensor?

Stock TBI systems will not tolerate much of a cam. Does it lope, at all, at idle?

I haven't noticed a stink and it is not setting any trouble codes. I believe all of this stuff was installed about 4 yrs ago (based on the paperwork I have) - I've had the truck for 2 yrs so I'm not sure if the ECM and chip are stock or were swapped out. I believe the system is designed to work with the stock ECM. The headers have an o2 sensor basically in the same spot as the stock manifolds do. Here are part numbers for what is installed:

MPFI - Edelbrock 3502 -
Camshaft - Edelbrock 3702 -
Headers - Edelbrock 65673 -
I think these are the heads, but will have to double check:
Edelbrock 60859 Performer Cylinder Head

From what I can tell, the truck has passed smog twice since this stuff was installed - when it was sold to the guy I bought it from and when I bought it.

[70c-10]

I had the coolant temp sensor swapped out and put in a 195* thermostat, also decided to swap out fuel filter since I had it already. I'm still getting similar readings for HC and CO%.

One thing that I did notice after the filter was swapped out is that the trucks starts much quicker.

I am reading that the stock chip has to swappped out in order for the truck to pass smog with the edelbrock stuff. I am going to go by the shop today and confirm that the chip was swapped out.

[70c-10]

i pulled out the ECM this afternoon and it does have the edelbrock chip. i found the postcard that you turn in to get the chip from them, so I was hoping that the chip hadn't been swapped and that was the problem.

I did notice that the exhaust does smell a bit. Not sure what else to try. I thought about swapping out the TPS, but a friend that's a mechanic doesn't think this is the problem.

[ChevyTech]

Originally Posted by ChevyTech

From your reply to this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=355812
...
You have headers. Are you running a heated O2 sensor?

With the high HC (raw gas out the tail pipe) you need to find the cause of the miss-firing. If the truck passed with this can previously then look at the other possibilities.

With the high CO also it may be dumping in so much fuel that the plugs are covered with soot.

All secondary ignition parts should be considered.

A mechanical problem like a flat cam lobe, or a cylinder with low compression, is a possibility.

[70c-10]

Originally Posted by ChevyTech

With the high HC (raw gas out the tail pipe) you need to find the cause of the miss-firing. If the truck passed with this can previously then look at the other possibilities.

With the high CO also it may be dumping in so much fuel that the plugs are covered with soot.

All secondary ignition parts should be considered.

A mechanical problem like a flat cam lobe, or a cylinder with low compression, is a possibility.

Thanks for the help. The plugs, wires and distributor cap were changed about 6k miles ago, but I will take a look and see if I can find anything.

If it's not something simple, I may have to apply for CAP assistance, since the truck qualifies (at least I think it does) and money is tight right now.

[70c-10]

Originally Posted by ChevyTech

A mechanical problem like a flat cam lobe, or a cylinder with low compression, is a possibility.

A called a friend to see if he could come over to listen to the truck run - to see if he thinks the noise I hear is a rocker making noise. I haven't heard back yet, but I hope he'll be able to make it over tomorrow or weds night.

Can you determine if you have a dead lifter vs. a flat cam lobe before pulling the engine apart?