Chevy & GMC Vans

Hi!
Again, more weird problems..
last time I posted a question, it was my steering box + PS pump, then brakes ect...
I don't know if I will see the end of that..

This time, I have some ignition or fuel problem.

During the holidays, I drove down to Florida. Nothing to say, I did the trip from Montreal to Daytona without any snag.
It's when I came back that I started to see some problems. It started on I95 near Jacksonville FL.
I noticed that when I was on cruise control, or at 70 miles-h, everything was fine, but when I was going down hill, or releasing the gas pedal, the engine started to hesitate, to miss.

And it became worst and worst.
If I accelerated quickly, pedal to the floor, the engine was running perfectly, but as soon I was decelerating, the engine was missing fire or something like that.
My worst nightmare was the toll plaza... the stop and go was a big problem.
So to avoid traffic, I drove 30 hours in a row, coming back by night, my girl friend sleeping beside of me...

When I crossed the border, in my country, it became so bad that I was sure that the engine would die in the middle of the highway.
Finaly, the engine died in my driveway!

Two days later, I took the plugs out, replaced them by the original one that I bought at the dealer.
I changed the plug wires.. the truck restarted quickly, but is still missing in the middle range.
On idle, it's perfect, if I floor the pedal, it runs perfectly too, but if I just put a little pressure on the pedal, to hold a fast idle or a 2000 RPM, it runs pretty roughly.
I changed the ignition coil, the fuel filter, cleaned the mass air flow sensor, replaced the cap and rotor.
Checked the fuel pressure, got 55 PSI..so it looks OK to me.
I don't think that the fuel pump is the cause of the problem, otherwise, I will get the symptom at any RPM..right?
I also went to GM and bought a new pick-up coil, (the sensor in T shape mounted under the rotor).
I don't have any codes...The engine check light is OFF.
At the worst condition, on the way back, I noticed that the check light was flashing (missfire detected)
But the light is now OFF.

Any idea?
I'm clueless now! #-o

what year Van?
sounds like a timing problem to me. On acceleration, the timing is advancing which is getting the timing into the spec range. On deceleration, the timing backs off dropping out of spec. My two cents ...

Check the distributor for worn bushings. My 96 Safari would random misfire at will. I changed the distributor after finding the top bushing was worn and allowed the rotor to wobble and that cured it. You might also look at the crankshaft position sensor.

Give it a vacuum test too.

Hi, sorry for the late reply, I was out.
It's a 97 4.3l..
I already replaced the cam position sensor, that's the part under the rotor that looks like a pick up coil on our lawnmower...
But it doesn't change anything.
For the distributor, I don't feel any play in the rotor, weird...
I didn't check for the vaccum, but the timing is mecanic and not electronic on this truck?
Is there any other sensor that I forget that can cause this problem?
Next step, I will strip it apart and sell the parts on eBay!

JeffSafari wrote:I didn't check for the vaccum, but the timing is mecanic and not electronic on this truck?

I am pretty sure there is no vac advance. It is ECM controlled.

Dean is correct. All of the timing functions are controlled by the ECU. The sensor inside the distributor is the camshaft position sensor. The crankshaft position sensor is in the lower right side of the timing chain cover.

How is your cat?

I replaced the cam position sensor, for the crankshaft sensor, is it accessible or it's another pain in the ass to remove?

About the catalist converter, is there a way to see if it's the cause? It really sound like a missfire, I don't feel any loose of power and on highway, it runs perfectly.

If it can help, the problem is worst when the engine is cold.
About a week ago, we got a -20 C and it started perfectly when i turned the key...
So obviously, I don't have any problem on idle...

To summarize what you have replaced:
Spark plugs
Plug wire set
Distributor cap
Distributor rotor
Ignition coil
Fuel filter
Cam sensor

It appears that all these have been replaced in an attempt to repair the problem without knowing what the fault is. I would suggest that for less than the cost of the parts you have bought, you could have got it scanned & diagnosed.

I could suggest numerous tests to do to try to diagnose but I would require some information that could be gotten with a scan tool to decide which direction to go in.

FYI: Flashing malfunction indicator light = cataylst damaging misfire. In other words, if your cat is not bad yet it will be soon if the problem is not corrected.

v8famvan wrote:malfunction indicator light = catalyst damaging misfire

Um, that means the error is currently happening. Steady on means that a code event has occurred and is stored.

Grumpy sets the P0302 (cylinder 2 misfire) at idle and flashes, then at speed the light stays on, when the engine returns to idle the light flashes again. When I clear codes at speed the light stays off, till the engine returns to idle and light flashes again.

Most auto parts will read the codes for free. Start by finding out the code(s).

Ok, you are right! I will bring it to the dealer and if I can get a trouble code. However, everything that I replaced are parts that I had to replace anyway on a good tune-up, so it's no big deal.
I saw the engine light flashing for less than a minute, but not anymore...
I will come back to you guys later next week, after the visit to a dealer.
Thanks for the help!

Wait, let me show you something.

Codes read at dealer = $$
Codes read at LAPS (Advance, AutoZone, etc) = free

+1 what Aaron said...
What about the EGR guys? At idle, closed ( or should be ). At high RPM closed, particularly when you stomp on it. in between should be open to varying degrees. Stuck EGR produces said symptoms.

Autozone will not do it anymore, at least in California. They will only sell you the tool now. They said due to a new law they are not allowed to read codes for people. I say, Lame.