Missed, difficult starting, intermittent

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m610

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Last year soon after I bought this truck I ran into this problem that seemed have been solved by replacing the starter.

Several months later the problem returned, and cleaning the MAF sensor seemed to do the trick.

About a month after that the problem came back and replacing the MAF sensor solved the problem, I thought.

Last week the battery died. Died as in suddenly quit acting like a battery. I replaced it and the problem seemed to go away, for about a week.

The symptoms, which are intermittent, are:
1. Misses when driving, but can drive fine for hours without missing.
2. Difficult starting. During cranking the engine will buck, or stop, for a moment, then continue, as if the timing was way off. When I stop cranking the engine sounds like it turns a little more, firing twice, weakly. Also, I smell gas.

Odd symptoms, for sure, but maybe folks familiar with Chevy V8s will be familiar with it.

I'm guessing another sensor, possibly the crank position sensor, or a vacuum leak. Someone suggested the ECU may be failing. I don't work on newer cars much, so... ask me about 1969-73 Opels and I can help. ;)

It threw a code the last time I drove it but my reader needs my laptop and the laptop is now on the charger. I should have the code within an hour or so.

Mike
 

m610

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Codes were P0300, random/multiple misfires, and P1380, ABS Rough Road/Misfire

Google (http://www.autocodes.com/p0300_chevrolet.html#ixzz3uw9riKZU) says possibilities pertaining to P0300 are:

- Faulty spark plug (s)
- Faulty ignition coil (s)
- Clogged or faulty fuel injector (s)
- Intake air leak
- Fuel injectors harness is open or shorted
- Fuel Injectors circuit poor electrical connection
- Ignition coils harness is open or shorted
- Ignition coils circuit poor electrical connection
- Insufficient cylinders compression
- Incorrect fuel pressure
 

m610

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This guy's page has been very helpful.

http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/testing-the-spider-fuel-injector-3

I'm getting one of those fuel pressure gauges today and will investigate that issue.

Other checks to do include smelling the dipstick, checking for the smell of fuel, an indication that the fuel pressure regulator is leaking. Also, spark plugs, to look for signs of problem injectors.

I'm not sure any of this relates to the odd behavior when cranking the motor, which really seems like a timing issue to me, but it's a start.
 

lesterl

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Did you neglect to mention your year and mileage?

I would suspect a few things for a P0300 right away. First thing to test would be a leaky FPR, another would be a bad "Distributor" Cap or coil wire.

Now don't just run out and start replacing things, we need to test things first.

Start by popping the plastic duct off the top of the intake. Open the throttle and use a very small inspection mirror and flashlight to inspect the inside of the intake (you can remove the throttle body to make it easier) look for signs of washing. Leaky FPR will cause clean area on drivers side usually and P0300.

If you replace the Cap/ Rotor, get an AC Delco unit.
 

m610

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Thanks, and sorry. It's a '96 with 225k on it.

I bought a fuel pressure gauge/tester. The regulator is the first thing I was going to check. Also, smell the oil, checking for gas fumes, and a few other things. Thanks for the tip on the intake.

The cap/wire may be more likely given how when cranking the motor acted like there was a problem with the timing.
 

lesterl

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Ignition timing is controlled by the PCM and the sensor in the timing cover plays a very big role in operation of the engines timing. Check the wiring to that also. If the engine is flooding out, check fuel injection and or the Coolant Temp Sensor near the thermostat.
 

m610

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The fuel pressure regulator checks out. I get 60 psi initially then it drops a little, to 55, but no farther, even after turning the truck off.

It really seems like a timing issue. I've got gas, and the planet still has air, but during cranking the engine will occasionally stop, almost, as if it fired at the wrong time. Once in a while, less often, I'll hear it puff back out the intake.

The distributor was loose. Not extremely so, but I could turn it by hand. In an older point system that would mess things up, although the distributor won't turn so much that the timing would be off by a whole cylinder. Of our, m,y experience so far has been with a 4-cylinder Opel engine.

I guess it could be the PCM or the sensor. I'll google to find out how to test the sensor.

Mike
 

lesterl

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When I set the distributor in my last Vortec 350 I had it set wrong and it did that, I advanced it a bit and the code went away and so did the hard starting/ backfire poof....
 

m610

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It didn't work for me. I turned it a little bit at a time and never got it to fire.

Then I looked for timing light marks. :) I guess there are none.
 

m610

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I can't find marks on my balancer, nor can I find marks on the block. It seems odd that I don't have to take a timing light to this engine to set things correctly.

There are scratch marks at the base of the distributor that the PO probably made so they could install things correctly after working on the car. I set the distributor back to that position.

I started digging into the ignition. Wires are new, plugs are new, cap and rotor were bad. It seems that was the problem. I'm a little disappointed. For all the grief this thing gave me I was hoping it would be something horribly expensive, to justify my frustration. Anyway, the truck, car, whatever it is, is running. Except, I took it out and during my brief freeway segment the check engine light came on again. I guess I know what I'm doing tomorrow. Also, the dash lights went out. Not the needles, but the background lights. Then they came on, then off. I guess the bulbs are OK.

Thanks all, for the help.
Mike
 

vbu2c5

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My 1998 Tahoe was running awful, missing badly and usually cranked for 3 or 4 seconds before starting. Complete tune up (wires, cap, spark plugs ) and it didn't help. Did some research on Youtube and found that the old poppet Central Sequential Fuel Injection style fuel injectors are a horrible design and needs to be replaced with the newer designed MPFI (Multi-Port Fuel Injection ).

It is a bit of a pricey item ( $340 or so ) but my truck runs so smooth now it's unreal, like a new truck! There is also a Youtube video showing a detailed instruction on how to replace it. You'll have to pull the intake manifold off and it's not a simple job but it is definitely doable by a shade tree mechanic.

You'll probably see a shiny aluminum washed section of manifold like what someone else mentioned before. That's the vacuum tube shooting gas onto the intake. This is not a safe situation and I've heard some bad stories about hydro locking and backfires blowing the intake off. Hope this helps.
 
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