engine trouble--need opinions

[sothpaw]

Hi all,

On the way home from an autocross, going up I-95 in heavy traffic in the rain, my newly
moded vette ran in to some serious engine problems. Basically, the engine speed would
become more and more eratic and I could not keep it in gear as it was bucking the car.

In other words, it was running rough, both at idle and under load, at any rpm. And it got
rougher until the engine stopped (well, I had a hard time pulling over in traffic the first time).

other facts:

1. Coolant and oil temps normal. (water pump should be good and is 1 month old)

2. Weather was rainy and 100% humidity, and I was following in traffic so there could
have been a little water spray on the car. But I did not hit a huge puddle that I saw.

3. Only code in CCM or ECM was CCM H74, which I am pretty sure is totally unrelated and I
have seen that before.

4. When I stopped, and waited, the car would run for a while and then it would happen again.
It seemed like the longer I waited, the longer it would run. At the end, my patience was thin,
and it didn't last 2 minutes, but then, I had only waited 5 or so.

My guesses:
Optispark: ? I just replaced one month ago, brand new, 1996 style, not refurbished. Still, this
seems like a classic Opti failure to me.

? I did have the car jumped last week when I drained the battery accidently.
? I have an Ed wright chip, Comp cam, new heads, timing chain, opti, and waterpump.

? Fuel pump? It started great every time I started it after waiting.

Thanks for any help!!

 

[Ken]

Think "plugging cats", maybe.

When it cools, the cat bed will shrink and allow the engine to breathe. When it gets up to temperarure it expands and chokes the exhaust to the point the engine will stall.

But that's just a three-thousand mile guess. :L

 

[Topless]

Right one goes first I seem to remember hearing.

Fuel vaccume?

My condolences on your road trip return. I know your pain. The last two road trips (back to back weekends) have ended up in repairs once I got home. This time I at least made it home.

 

[BigRed]

Do you have an open air box?

What might have happened is you got water into the engine and it eventually died.

Also when you installed the Opti could it have been damaged or sealed unproperly causing the weather you had to kill it?

 

[sothpaw]

Ken,
Plugged cats are interesting, as it did make that sound the exhaust system makes when
you are at high rpm after a down shift and decelerating. I thought that was the mufflers or the exhaust pipes being too restrictive for the load.

Big red,

Yes, I have the triple claw, but again, didn't go through a huge puddle and the claw doesn't suck air through the fan shroud. I just sits where the stock box was, and breathes in engine compartment air. Anyway, why would letting it sit help this?

 

[Ken]

When my cats (3) were rattling and making a lot of noise (I actually thought it was the connecting rods! :eek) the car would run just fine. But if they got quiet, it was as if someone stuffed a potato in my exhaust outlet; the car wouldn't get out of its own way. If I pulled over and allowed it to cool it would run fine again, for a while.

I replaced all three at the time, now I don't run any. :L

But then, I'd be illegal even in Puerto Rico!

_ken

 

[sothpaw]

Ken,
Come to think of it now, I did here a metallic rattle or something during the first incident, I just didn't know if it was the car or something on I-95.

Do you think if the opti was wet that it would act like this?

 

[Ken]

The OptiSpark would probably, unless it just dies - I don't know, cause some sort of pinging if it was mis-firing I guess.

 

[vee93]

This might read as too simple, but check this out:

I too, was having similar bucking problems (I have a '93 auto).
After having everything checked on the car that was imaginable with no codes, I was also contemplating the purchase of a new OptiSpark.

Then it occured to me to service my K&N filter (flat filter w/open air lid). The instructions for the filter give a good leeway in miles before cleaning. It was going on a little over 10,000 miles since the last cleaning, but the car had been in a body shop for a couple of months. The body shop folks detailed the ex-and interior of the car. I'd seen it a few times while it was there and it was always covered with some kinda fine white dust.

Forgetting this when I got the car back, I drove it and started having these problems-like the fuel was cutting off if I stepped on the accelerator at a little over 40mph, between 1200-1800rpm. A $1400+ tune up seemed to solve the problem before the car went to the body shop.

Basically, I cleaned the filter. And with the exception of a couple of times, the car runs exceptionally well. I think when the problem has repeated itself recently, I might've been just trying to stay around 30mph in a residential area and not giving the car gas-just pretty much letting it coast on its own after giving it just a little gas.

When's the last time you serviced those 3 conical filters on the "claw"?

 

[sothpaw]

I haven't serviced them.

They are 1.5 years old, with 7000 miles on them. I don't think
you are supposed to have to clean them so often.

Another relevant fact--this car came out of the shop w/new heads/cam/optispark, and I have autocrossed it twice and
drag raced it also. I scored a good time at the drags (considering the tires), so I wouldn't understand the sudden change.

 

[gmhowe]

I had the same problem with my 85, it was the Fuel pump for mine, when I replaced it I had the strainer cross ways and it would impede the fuel flow, took several months for me to finally figure it out. what a pain

 

[sothpaw]

Fuel pump/ injectors are also looking like a hot possibility.
I understand that my new heads/cam are putting more stress on the injectors and maybe the pump. I thought with drag race and autocross use, where I am not staying at the peak rpm long, that they would be ok.

perhaps not.

 

[afree]

I have had two similiar incidents with my 1988 Coupe. Both occurred on a return trips from out of town after the car had been run for a while.
The car basically died while sitting at a stop sign (both times). I managed to get it started and out of traffic but it ran very rough. Checked codes, none logged. I Allowed the car to cool for a while and started it up again. Ran fine for a few seconds to a minute. Sounded and acted as if it were being starved for fuel. After some investigation I removed the in line fuel filter and found that I could barely force any air through it at all. Replaced the filter (both times) and solved the problem. I assume that by allowing the car to set for a period some fuel, due to pressure, would get forced through the filter. At least enough to start it and run it for a short time.
Hope this helps and let us know what you discover.

 

[rrubel]

Other possibility, maybe, is that with the autocrossing you stirred up whatever sediment is at the bottom of your tank and clogged the fuel filter that way (or the pickup sock on the pump). Shutting the car off, removing the pressure in the system, might allow the gunk to settle a little until the car is restarted.

See, you need to drive the car MORE!

[RICHR]

 

[sothpaw]

I could get the car to run 10-20 minutes if I waited long enough.
So I am not sure. The engine temp seemed normal, so I can't tell if it's starving for fuel (too lean would heat up).

So, what to do about bad gas? Just the fuel filter?

I think I will stop by if it's not raining and see if I can get the
car 25 miles home.

 

[vettenick]

Borrow a fuel pressure gauge, hook it up and drive the car. Watch the gauge when the car acts up. If the pressure drops, you're on to the problem...either a pump, filter, or fuel supply problem.
To check the cats, hook up a vacuum gauge to the intake. Slowly bring the engine RPM to about 2500. If the needle starts to slowly drop, look into the cats starting to block. If the engine can't breath, it can't generate vacuum.
Good luck!

 

[vettenick]

By the way, if you discover that the cats are blocking, you should determine why they blocked in the first place before you spend the money to replace them. Otherwise, you could be doing this again in a few months. Especially if it's running on the rich side.

 

[rrubel]

Sothpaw, I've got a vacuum gauge and a fuel pressure gauge here. You're welcome to stop by and borrow them.
[RICHR]

 

[sothpaw]

Rich--may take you up on that.

I think it's probably the blocked cat. Here's why:

I brought it home Tues. night, and as soon as the engine hit 190 deg. oil temp, the roughness began. I let it cool a few minutes, and it did it again. Finally, I let it cool longer, with the hood open, and put towels on the cats to cool them. This got me home before the oil temp got back over 190.

If it was really a fuel problem, why would it happen only when the engine warms up?

Nick--what causes a blocked cat? I thought just age? I guess I would just gut/inspect the cat when I remove it?

 

[vettenick]

Fuel pressure/delivery problems are usually evident all of the time.
For example, if the car was running rich, your gas mileage will be off, or you may notice black smoke at times. That's an extreme case. A more subtle situation would be where one or more of your sensors could be off just enough not to trigger the "check engine" light, but to create a situation where the engine is using more fuel than normal. Even a computer that may be going bad too! Over a long period, this would cause the cats to work overtime to clean up the exhaust. One of the tools that the cat needs is the heat that it generates to force the chemical reaction. Too much heat from a rich mixture could crack the ceramic and thus cause the monolith inside to break apart. When these pieces work their way to the back of the converter, you get a blockage.
Get a scan tool to monitor the computer's sensor values. Look at fuel trim too. And check the fuel pressure, just to make sure.
If you want to do that, I will walk you through.
Then, if all is well, it was probably old age, or even vibration (hitting bumps) can cause the cat to break apart. It's happened to me. If you're lucky, that's all it will be. If not we'll figure it out.