94 TBI Blazer cutting out

I think this thing wants to sit in the garage the rest of its life. The truck was poping or back firing throught the TB when I stab the throttle. It was acting like a lean pop. Didnt make much sense because I just put the new fuel pump in and I am running about 14 psi fuel pressue. The tune has not changed other than me adding the $OD fan code to it. The truck has been sitting for over a year due to paint and body work so keep that in mind. While watching my wide band I could see the AFR go to nothing when I stab the throttle causing the pop. It is almost impossible to drive it this way. I logged it and every thing looks good, BLM's 125-129, IAC counts in the 20's.

I started swaping parts out that were easy to change to see if I could find anything, the TPS, and MAP.
I installed a hose to run my fuel pressure gauge out from under the truck and there is no drop in pressure at any time.
What I did find was that the coil wire did not fit the coil very well, when I took it off the post on the coil had corrosion on it, I cleaned the corrosion off and put so dielectric grease on it. I also squeezed the connector so that it fit the coil better. This helped the pop at idle, gone, but when driving under a load the truck shakes and cuts out pretty bad. I am thinking it may be plug, wires, and cap time. The pickup in the distributor, looked pretty rusty. It may need one of those too. This one is not that old, bought from Advance Auto Auto 5-6 years ago. The wires are crap too 7mm autolite stock type wires. I am thinking a nice set of 8.5's. Any input?

What did you do to motor since it ran?

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The truck has been sitting for over a year

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That's about 9 months longer then ethonol enhanced fuel lasts... I fixed the neighbors brand new last year lawn mower, sat 6 months and would not run. Pulled float bowl to find a bubble of water in bottom, corrision around level of gas. Drain, flush and new gas and ran great. Last year after fixing 2 lawn tractors and several other pieces of gas equiptment for a freind I talked him into using non ethonol fuel all year, plus stabilizer for winter and everything ran this spring.

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Originally Posted by EagleMark

What did you do to motor since it ran?

That's about 9 months longer then ethonol enhanced fuel lasts... I fixed the neighbors brand new last year lawn mower, sat 6 months and would not run. Pulled float bowl to find a bubble of water in bottom, corrision around level of gas. Drain, flush and new gas and ran great. Last year after fixing 2 lawn tractors and several other pieces of gas equiptment for a freind I talked him into using non ethonol fuel all year, plus stabilizer for winter and everything ran this spring.

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I really have not done anything to the motor. I hooked the purge canister back up, but plugged it off again to see if that was causing it and it was doing the same thing. As far as gas the tank has been drained bone dry, cleaned out. It also got a new fuel filter with the fuel pump. I just had the injector pod apart to check the regulator and did not find anything abnormal as far as gunked up fuel. Watching the injectors spray, I did not see anything wrong either. I may get a set of wires and plugs, since after messing with that coil wire the issue seemed to get better.

You may be on to it with ignition? A guy on CK5 had same issue, got zapped while moving around plug wires and had an arc a distributor cap, got rid of arc and half issues gone. Without an Osiliscope as a sure fire way to see what all 8 spark events look like the only way I know is to look under hood in pitch black darkness for arcs. He found several arcs in darkness. He also found something really strange! Saw a fast flashed type glow? Turned on flashlight and it was coil, he could see inside coil!

Even though you have new fuel, just wanted to let you know what I've found lately, last couple years. Ethanol enhanced fuel does not become gummy or have that old stale gas smell that your used to, well not at 1 year or so. Still looks and smells like gas. But if you look in tank like I did above in float bowl... look to bottom corner where water would settle in gas and you'll find a big bubble of water. In a lawn mower float bowl it was size of quarter! I know ethanol attracts moisture but this has happened in sealed systems? In short time? Like it seperates? Then no longer fires enough in cylinder? I don't know exactly what's happeneing but it's a PIA! Got fuel? Check. Got spark? Check. Sounds like compression? Check. Should run or at least try? Seems Craigslist is loaded with cars for sale that ran great when parked 1,2,3 years ago. Usually I can make them run real quick... (take out 50% for liers that parked car because it didn't run)

That reminds me, I have a gas can in shed with about a gallon of ethanol enhanced crap I left there on purpose last year...

It's very difficult to get ethanol free fuel here so I see plenty of issues from 10% ethanol fuel. As described this problem does not seem like an ethanol issue.

Of course the first thing to do is try the last known good calibration to see if the problem clears up. If the engine still runs poorly you can proceed with diagnosis.

If spark isn't being delivered to the plugs the O2 will read lean because fuel and O2 are unable to react to form CO and CO2. Testing is a generally matter of eliminating components that could short circuit spark enroute to the plugs. A spark tester is a great way to check for spark. Try installing it in various plug wires and check for spark under conditions where the problem occurs. Move closer to coil by installing tester inline between coil wire and cap, then coil and coil wire. You can also connect a test light to ground and gently slide the tip along the plug and coil wires and along the epoxy insulation of the coil. Or you can use an inductive timing light on each of the plug wires and the coil wire to look for "missing" flashes. You can even mix up a mild salt water solution to spray the engine down to locate bad wires or shorts.

"On a side note, if you're having trouble selling a tune up on a car with faulty plug wires you can use a spray bottle of 90% rubbing alcohol to sparingly mist the engine while the customer watches. The resulting ball of flame is guaranteed to dislodge cash from wallet.

Notice the spark tester in this video. This is the only type I trust 100%. You can see and hear the spark and it's loud enough to hear over most stock engines. In a pinch you can make an effective tester by clamping a ground wire to a spark plug and opening the ground strap to .100" (that's 100 thousandths of an inch). The voltage test is the same but you will not hear the spark like the professional tester. It takes 30,000V for spark to jump this gap so if you put it inline with a spark plug you're causing the system to create 50k to 60k volts. If there is anything wrong in the system it will show up here.
http://www.youtube.com/watch?v=z47TliL4OJ4

Finally, if the spark test doesn't show a problem you might check for AE pulses when the throttle is snapped. If the TPS is failing the ecm may not be delivering correct pulses. TBI Injector pulses can be viewed by shining a timing light at the injectors while the engine is running. Often times, disconnecting the TPS and allowing the ecm to set a code will be enough to restore some driveability if the TPS is failing.

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"On a side note, if you're having trouble selling a tune up on a car with faulty plug wires you can use a spray bottle of 90% rubbing alcohol to sparingly mist the engine while the customer watches. The resulting ball of flame is guaranteed to dislodge cash from wallet.

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:laugh:

I may have to try this for kicks, but my Osiliscope works with much less flare!

Farmers didn't trust the oscilloscope. Thought I was trying to sell them something with that high tech machine. But a ball of flame! Now that's something they understood.

Wow, now thats pretty funny! I never thoght about trying that to trace down an arcing plug wire. I can get my hands on a scope! I may just go that route. I did make some progress today though. I changed out the plugs, wires, cap and rotor. The plugs were pretty funky looking. I thought for sure I had it. The truck runs 1000 times better but I still have a small miss that comes ond goes. It runs really good up top, but down low when I lug it, I get a small miss. I do have an extra coil, I may stick it on before I spend anymore money. The wide band does seem to go nuts when the miss/flutter happens, like you said it will not pick up the un-burnt fuel and show as lean.

I have a nice timing light too, but I did not think about moving it around to different wires.

I still think my Dizzy may be suspect too. Summitt has a nice billet replacement and a set of 8.5 wires that may be comeing its way. Then I will just take the other stuff back.

I went ahead and started over on my tune this weekend. I think I had 2 things going on. The cap, button, wires, plugs, module, and coil got rid of the miss. But, that lean pop was still there. I logged the truck with my LM1 running through my Autoprom and pin pointed some lean spots along with the help of the BLM's and the Datatrace trace feature in Tunerpro. I have to say that is really cool. That was the first time I used it and it was a big help. I also went ahead and modded the FPR and now I have a solid 15 PSI fuel pressure. I think that really helped the idle quality, its really smooth now. I do not ever remember the truck idling this smooth since I put the motor in.

I think some of the lean pop is coming from not enough AE, I went back and looked through some of my old tunes and I was using a lot more AE so I am going to give that a shot. But, I am getting closer.

It turns out that all my problem was in the tune. Truck is running great now. I ran it with the AC on yesterday and was feeling a little something so I logged it again. I need to work on my decel enleanment tables some more.

Hard to have a good tune with all the issues you've fixed? Glad your going the right direction!

I'm sure the billet distributor with melonized gear will be fine. But as far as aftermarket EST/ICM there are huge differences in timing it produces. Sticking with a GM AC unit is by far best choice. Get one that is 369, not 048. Good read:
http://www.thirdgen.org/techboard/di...ncy-table.html