95 4.3 w 4x4 Blazer, runs bad and stops

Hi all!

I've got a "new" Blazer -95 4.3 vin W about a month ago. It has run about 170,000 km.

But now it looks like it was a bad buy, it runs bad. The rpm starts jumping between 1500 - 2500. Suddenly the break and ABS warning lights in dashboard lights up, and sometimes all black out and it stalls.

At first it started acting like this when towing a trailer on the highway, doing 80 km/h. But now it does it at any speed.

Any ideas?

/Freddy

Do the rpm's jupm when at idle or when under power?

Do the rpm's jupm when at idle or when under power?

First it was under power but now it jumps at idle too, but not as much...

EGR valve

Yeah could be EGR , vac leak, IAC, MAF, TPS, Ignition switch and more. You should go get some codes scanned. Its ODB1 so make sure they can do it before you go. Most auto part stores will do it free.

Thanks for your inputs!

It's not OBD1, it is the typical -95 OBD 1.5 that I must go to the special "Chevy" repair shop too get scanned. They charge about $100-$200 for doing a scan.... (I live in Sweden). My OBD2 scan tool do not work on it...

The Check Engine light is not on, but I guess there still can be some codes stored.

I think it acts like the ECM/VCM restarts when driving. But first it does the jumpy rpm thing.

/Fredddy

is it a specific amount of time that it takes to start running good?

When it all started it ran good at first but after some time the problems started. On Monday it ran for 20 minutes with no problem but yesterday (Saturday) problems started almost at once. Today it's hard to start, miss a lot and stalls at idle. Exhaust smells of gas.
I'll have a new look at it tomorrow...

You will have to test the fuel pressure.

Today I checked the fuel pressure, it is 60psi when fuel pump is running.
When fuel pump stops the pressure drops immediately to 55psi.
In 5 minutes it bleeds down to 48psi.

Today it did not want to run, it started at first and ran very poorly. Petrol and sot sprayed out of the exhaust.
Video (http://youtu.be/4_nhT9h8h0E)
Then at next start attempt it just cranked and once in a while a cylinder fired...
Don't know if it is because of too much fuel or bad ignition...

Had another go at it today. Again the first start it runs for a while, missing a lot. But after some time it wont start at all, just crank.
Today I swapped the ignition coil and module, had a look under the dist cap witch looked fine and new. Previous owner must have replaced cap and rotor...

Opened up the intake plenum and had a look at the fuel system in there. Did not see any fuel leeks when I primed the fuel pump. All poppets/nozzles looked fine too.
Whats next?

I would guess it would be a leaking poppet or a bad fuel pressure regulator. The fuel pressure should not drop like that so it is not keeping pressure. It should not drop more then 10psi in 15min.

Look for a clean spot that is free of carbon in there. that is a sign that gas is spraying. If not try a fuel pressure regulator.

Fish, I thought so too.
But I did not see any leak when I looked at the regulator and poppets. Thou the right side (regulator side) of the plenum was cleaner than the left side...
Should I not see the leak when running the pump?
/Freddy

its hard to say. I would think that you would but I guess it is possible you could. I would toss a new pressure regulator in and test it for holding pressure. I think they are cheap enough. At least here in the states.

I think I solved the problem!
I checked all sensors in the ignition and fuel injection systems, and found that the previous owner had replaced the CrankPositionSensor. It sits almost under the engine, in front. When I unplugged the connector I found that the rubber seal was missing!
I sprayed it with some 2-26 electric cleaner and put in a new seal. Now it runs great!

The problem was that the VCM did not get signal from CPS and did not send correct ignition signal. So it missed a lot, soaking the cylinders and spark plugs with fuel... (the CPI system spray fuel from all poppets at each ignition pulse)
That explains the very rich running and fuel in exhaust, that led me in on the fuel track...

Now I may find some time to work on my other blazer with the transmission problem (missing third gear)

/Freddy