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Discussion Starter · #1 ·
Some of you may have been following my progress in Brock's thread in the blowers and bottles section. Well, now I'm trying to troubleshoot another problem.

I have a 94 TBI, fully rebuilt with 2114 intake manifold, 2002 vortec heads, new pushrods, lifters, etc etc. I know my idle is a little too low right now, but that will be fixed soon.

My main problem is that when the engine is cold or it is cool outside, the engine bogs down and backfires in the intake upon acceleration. At higher rpms and when warm, it runs pretty well. I don't have a fuel pressure gauge yet, but I wanted to troubleshoot this problem as soon as possible. So...where should I start? I don't want to start replacing things until I'm almost positive of the cause. From the research I've done on the forums, here are a few of my ideas...

1)Possibly the plugs are gapped wrong? I have NGK's in there, but I'm not sure if the shop gapped them correctly.
2)EGR valve was removed since the new intake manifold has no provisions for it. Are there any other sensors or connectors that are EGR related that I can unplug/remove?
3)Could it be a bad map sensor? I'm not getting any codes, so I'm not sure. Like I said, I removed the egr stuff, so is it possible that this is giving it trouble?

any other suggestions/comments would be greatly appreciated!
 

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Discussion Starter · #2 ·
Would excessive running at low rpm foul up the plugs? I'm starting to think more and more that this is the culprit. This afternoon I'm going to remove a plug to see if it's gapped right and also see if it's fouled up. I data logged some information on how everything was running a couple days ago, and it says it's idling at 650, which seems pretty low. Man, I really need that new chip soon.
 

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Discussion Starter · #3 ·
I'm not sure if anyone is really even looking at this thread, but I'm still having trouble. I've checked the plugs and they look fine (just like brand new). I also just replaced the cap, rotor, and plug wires. Although this fixed some clicking noise I was getting in the radio, this didn't fix my main problem. I removed the rest of the EGR junk and plugged the vacuum lines that went to the EGR. No change.

I got the new chip and installed it, but to no avail. It still almost stalls out when I'm slowing down nearly at a stop. And it still backfires in the intake when it's cold and I'm accelerating.

Could this be a bad O2 sensor? I'm not getting any codes mind you. One thing I did notice when I first got the truck back is that the connector for the O2 sensor was just hanging down. Apparently they had forgot to hook it back up. I also noticed they broke the clip off of the connector. :rant: I tried pushing the connector back on, but of course it didn't "snap" in.

I guess my next to tries will be checking for vacuum leaks and replacing the O2 sensor and maybe the connector as well. Argh, such a pain!

And yes, I have a datalogging program & laptop, so any information on what I should look for in the sensors would be great.
 

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Static> Bags
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Mine was popping back throw the TBI and it was a vacum line off, hooked it up ran fine.
 

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Static> Bags
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i forget now, that was like a year and half ago when i was driving the truck.
 

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Discussion Starter · #8 ·
Ok, today I replaced the TPS per someone else's thread. At first it did seem to be running a little better, especially when coming to a stop. I thought everything was going to be fine and dandy. Then as I pulled into the parking space at my apt. it stalled out completely. :rant:

This is really starting to piss me off.

so far..new:

IAC
TPS
plugs, rotor, cap
knock sensors
ECM chip
 

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91 S-10 Pickup 4x4
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if its backfiring through the TB, then check your timing with a timing gun. When it backfires throught the TB< thats a sign of the timing being to retarded. On your truck you are able to adjust timming. Make sure you discinnect the brown wire under the dash first.
 

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Discussion Starter · #10 ·
91S104x4 said:
if its backfiring through the TB, then check your timing with a timing gun. When it backfires throught the TB< thats a sign of the timing being to retarded. On your truck you are able to adjust timming. Make sure you discinnect the brown wire under the dash first.
Yeah, I had the timing adjusted once before I had the IAC fixed. Later on when I ended up changing the cap, rotor, and plug wires I probably got the timing off a hair or two. I'll probably take it by a shop sometime tomorrow or this afternoon to get the timing re-set (don't own a timing gun). At least once i get it set, that'll be one more thing out of the way. Thanks for the reply.
 

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Gaaoooooo
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Changing the cap and rotor shouldn't have changed the timing I don't think, but it doesn't hurt to have it checked.
 

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Discussion Starter · #12 ·
MINTSICK said:
Changing the cap and rotor shouldn't have changed the timing I don't think, but it doesn't hurt to have it checked.
Ok, I had to remove the distributor because I couldn't for the life of me get the rotor off the top. It was stuck on pretty good. I had a little trouble when reinstalling it. I mean I doubt this is the main problem, but maybe it'll help me diagnose it. I'll let ya'll know how it goes.
 

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Discussion Starter · #13 ·
Alright, another update. I went and got the timing set. The mechanic advanced it a couple degrees. While we were looking back there we saw that the vacuum hose that goes to the intake manifold from the vac ball was kinked. It was an old hose and pretty brittle and had folded down on itself. I ran to Advanced Auto and put a new hose on there. So far the truck is running a lot better and not even pretending to stall when I stop. I'm a little apprehensive though, because it has done this before...ran fine for a few miles then gone back to crap. I'll make another update as soon as I've driven it around a bit more. I'm gonna be so mad if it was just that old hose...
 

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Discussion Starter · #14 ·
Small update...

Still running like crap and starting to get worse. Replaced the M.A.P. sensor today and it did nothing. Tomorrow I'm breaking down and taking her to the mechanic :( I need to go play some guitar or something. Argh! :rant:

I'll let ya'll know how it goes and how badly I get raped by the mechanic.
 

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Good Bye SonomaST
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do u have a loss of power?
 

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yes, that is a v6
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what cam are you running? dont you plan on running some boost one day? if so, i would buy a boost/vacuum gauge now and hook it up and see how much vacuum you are pulling at idle. it sounds like a vacuum leak to me. some of those plastic lines can fracture and its nearly impossible to see
 

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Discussion Starter · #17 ·
s10ls said:
what cam are you running? dont you plan on running some boost one day? if so, i would buy a boost/vacuum gauge now and hook it up and see how much vacuum you are pulling at idle. it sounds like a vacuum leak to me. some of those plastic lines can fracture and its nearly impossible to see
I'm running the Comp Cams 266hr. I'm leaning more towards a vacuum leak as well, but I don't really have the tools to check the vacuum pressure or anything. I'll let ya'll know how it turns out.
 

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Discussion Starter · #18 ·
Ok, here's the low-down. Took it back to the shop. No clogged cat or anything like that, O2 sensors seem to be functioning properly. No check engine light was showing either. I decided to check the codes just to make sure I wasn't really getting a code. Upon checking the code, I get a 28, which is Transmission Range (TR) Pressure Switch Assembly Fault . I don't know why it wasn't showing up on the SES, but it was in the trouble code. This fault makes a lot of sense now. The only problem is that I can't get around to taking it back to the shop till Monday. But at least I'm close to figuring it out and hopefully getting it fixed.
 

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Discussion Starter · #19 · (Edited)
Update for anyone who cares...

Brian at tbichips.com took a look at some of the test data I sent him and notified me that the O2 sensor was going haywire and wasn't warming up properly. I replaced the O2 sensor then checked my plugs. Apparently it was running pretty rich, b/c the plugs were coated in black. I replaced the plugs as well. I also got a new program from Brian (which I burned myself with the awesome stuff from moates.net) and it's running much better now. This is probably the best it has run so far. It's still a little buggy in the data, but I haven't given it much time to learn everything. I'm hoping it'll improve after I drive it around a bit. It's just nice to have a truck that runs decent now :)

Oh, and I cleared the transmission code and it hasn't come back so far, so maybe (crosses fingers) it was just a fluke.
 
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