95 engine pop (backfire)

rpederson · #1 09-29-2005, 08:34 AM

Here is one that I cannot figure out.

My 95 blazer has been giving me an engine pop or backfire warm or cold. I do not have the "check engine" light on yet. I have replaced the plugs and wires. Still happens. I am wondering if the Dist. Cap could be bad.
I have the odd dist.cap with horz. towers. Also, could I have a poss. vacume leak? :

Cailen · #2 09-29-2005, 11:26 AM

What plugs did you use and what was their gap?

rpederson · #3 09-29-2005, 02:22 PM

AC Delco Gap of 35. The vehicle was doing this before I changed the plugs.

I went to Auto Zone and I do not have any codes coming through

Cailen · #4 09-29-2005, 03:51 PM

Ever had the heads off? Ever had the lower manifold or cpi worked on? I ask because if your distributor has ever been removed there is a chance that it could be off by a tooth. I don't know if it's possible for it to jump a tooth.

I would recommend getting your timing checked.

rpederson · #5 10-01-2005, 02:01 PM

Never had any work done to the engine at all--Never needed it. It has great power with hestitation. I have done some research and have found that with the Horizontil cap, lke the one I have, there is a seal between cap and Distrib. I am replacing the cap today with new seal. I'll let you know how it turns out.

If you have any other sugestions--PLEASE--let me know

Thanks!

Cailen · #6 10-01-2005, 02:49 PM

Do you have the correct wires for a horizontal cap? If the wires' connections at the cap have a right angle then you have incorrect wires.

rlith · #7 10-02-2005, 06:34 AM

Quote:

Originally Posted by rpederson

AC Delco Gap of 35. The vehicle was doing this before I changed the plugs.

I went to Auto Zone and I do not have any codes coming through

You should be at a gap of .45 not .35... Secondly, pull your upper plenum and check for washing, you could be dumping fuel

rpederson · #8 10-02-2005, 07:05 PM

Ok--I checked the plug gap and I have a .45 not .35.

In an earlier post I meant to state the it does NOT have any hesitation.

Now today, I went out to move the vehicle. It started hard but finally fired up. I backed it out of the drive, parked it, and proceeded to do my weekend cleaning of the inside. Now it will not start at all. I replaced the cap and rotor--no good--still will not start. I read through the forums and discovered that with many who have the same problem found that the CPI was or could be the culprit. I hate to sound stupid, but, is the CPI the round, black item in top of the upper plenum? How can you tell if it is bad?

rlith · #9 10-02-2005, 08:01 PM

No, that's the throttle vane, the CPI unit (fuel injector) is inside the upper plenum... Pull the plenum and check for washing

rpederson · #10 10-02-2005, 09:55 PM

Ok. Thanks.

rpederson · #11 10-03-2005, 06:11 PM

Now I am really confused! I had the Battery charger on the vehicle all day to bring the charge up after cranking on it all day yesterday. Got home from work, Stuck the key into the ignition, turned it over AND it fired up! No poping! No Backfire!

I drove it around town for over an hour, turned it off several times and it fired right up. What I heard tonight that I did not hear yesterday was the fuel pump kick in before starting it. SO, my question is..........Now what?

rpederson · #12 10-04-2005, 08:31 AM

No start again this morning. I am beginning to thing that I may have bad ignition switch. Any thoughts?

Cailen · #13 10-04-2005, 01:00 PM

Or bad battery connections. Maybe clean em up, and while you're at it have your battery tested at your local parts store. That wouldn't be causing your backfiring, but lets get your truck started first.

Does your truck even crank? If so, can you start it by pressing the gas pedal? Do you hear your fuel pump prime when you turn the ignition to the on position?

As well you double checked that the wires you have are for your horizontal cap and not for a vertical cap right? I had a parts guy mix it up on me.

To check for CPI problems take the Vortec nameplate off your upper plenum, remove the IMTV valve (round thing right below the name plate) and have a peek in. It should be completely blackened and carbonized inside there. Take a flashlight and look for clean "washed" spots or even pools of fuel. Clean spots on the passenger side indicate a leaky fuel pressure regulator, and clean spots on the drivers side indicate holes in your "nut kit" (inlet / return lines).

Lets us know how you make out!

rpederson · #14 10-04-2005, 06:04 PM

IT'S FIXED! I towed it to a nearby garage this am and told him what was going on (a young kid about 20) and he tested the fuel pressure and pump voltage in about 20 minutes. Voltage is great, pressure was not--because the pump was not running like it should when you first turn on the key--at times I could hear it run, but not always. He turned on the key, crawled under the truck, and tapped on the pump. The truck then started.

I left it with him and he replaced the fuel pump. It runs great!!!!!!!!!! No more popping and backfire. Idles a lot better and I even got a small "chirp" from the tires when I took off from a red light. I also had him change the oil, because it needed it. Total cost (parts and labor) $235.

SOOOO, now I get home and the wife wants me to trade it in!?!?!?! I think not!

Thanks guys for all your help.

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