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'88 350 TBI Running Extremely Rich in Closed Loop!

K

kp texan

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Corpus Christi, TX
*PROBLEM SOLVED, POST 12*

My '88 K5 started to run erratically a few months ago so I just parked her until yesterday (she's my beach vehicle). I had a hunch that since the tank was pretty much empty and that the gas was old, my trusty Blazer just needed some good gas in the tank. I poured 5 gallons of fresh gas into her and, with a fresh charge on the battery, she started up with minimal fuss. It idled fine and seemed to rev okay too. I was thinking: problem solved!!! I let my K5 idle for a bit and then went inside to wash my hands. I heard the idle speed kick up when I was inside the house so I came back out and realized that at was running extremely rich. When I tried to give it some gas, it started to bog and there was a very strong smell from the exhaust (it was actually next to my fence and unburned fuel was spraying all over it). After trying to rev it for a few more seconds, it finally bogged and shut itself down. It appeared to me that it started running badly in closed loop so I had a spare O2 sensor and changed it out. Still didn't fix the problem. The next thing I'm going to take a look at is the coolant temp sensor because I've seen in the past that it can make an engine run too rich. Could you guys please give me pointers on other areas I need to be looking at??

Thanks so much,

Wes
 
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The check engine light was on and then it went back off. I pulled my negative battery cable off after installing the new O2 sensor so it probably erased my codes.

Thanks,

Wes
 
It might be an ignition problem, if you are getting raw, unburned fuel coming out of the tail pipe.
 
Whats odd is that it seems to run just fine in open loop. That tells me that it may be a sensor issue. Are there 2 coolant temp sensors on the 350TBI or just one? If there are 2, which one is linked to the computer?

Thanks,

Wes
 
Should be just one coolent temp SENSOR, and a coolent temp SENDER, if you have a temp gauge.

Are you sure it was raw fuel coming out of your exhaust, or just moisture that smelled like fuel from a rich condition?
 
I'm fairly certain that it was raw fuel since the exhaust started burning my eyes. It was wet and soot was hitting the wooden fence as well. I suppose it could be some condensation. Like I said, the odd thing is that it ran fine when I first started it and it could be reved normally and everything. I would think that would indicate that its firing on all cylinders.

Thanks,

Wes
 
i would take off the air cleaner and look at the spray pattern. maybe clean the throttle plate and the IAC. looking at fuel pressure wouldn't hurt
 
go through these voltage checks if you can.

http://www.binderplanet.com/forums/attachment.php?attachmentid=28690&d=1192805191

also check fuel pressure at idle and under load. If the check engine light comes on again find out what code it is throwing. (theres a thread on here somewhere about how to do that)

It only takes a few minutes to go through those voltage checks if you back pin the ECU with a T-Pin or similar. With that info and the fuel pressure you can usually get a clear idea of what is going on.

without doing the proper diagnosis work you are just gonna be guessing. With the time it took to swap the 02 sensor you could get the voltage checks done.
 
if it was running roough, this would be a sign of missfiring, and the only way raw, unburned fuel can make it through the engine without burning is if the ingnition system does not burn it.

If too much fuel was dumped into the engine, this could cause fouling plugs, and a misfire. Open loop would not feed enough fuel to the engine to foul the plugs, but a bad fuel injector could.
 
I paraphrased this from a previous post of mine

I had a broken lower injector o-ring once. It would run really rich, as much as blowing strait carbon out the tailpipe, and a lot of black smoke. Barely any useable power. It would run fair when it was cold, but when the engine was up to operating temp, it would drive terrible.

I tested things for days and couldnt find it. I used my timing light to show me the injector patterns, and thats when I saw the fuel droplets. With the TBI, the fuel cavity fills up with gas, then the injuector sucks the gas from that pool and shoots it into the intake. Without the lower o-ring, all of the gasoline runs strait into the throttle body.
 
Looks like my problem is solved!!!!! When I got home this evening, I cranked up the old Blazer and she started running rough as expected. It bogged and stalled out which made the CEL come on. Used a paper clip to check the fault code and I got a 15: low temp indicated at ECT sensor. Long story short, I threw a new ECT sensor in there and a new thermostat for good measure and she started up a bit rough but then began to run normally. Drove her around the block several times and she ran like a champ! Now the idle has settled back down to normal and you can floor it without any bogging. Thanks for all your suggestions and help!! I just happened to luck out and it was a simple solution.

Thanks,

Wes
 
I had the same deal with the 90 Blazer I recently bought. In fact one of the reasons it was cheap was the seller couldn't figure out what was wrong, and didn't want to pay someone to fix it. After asking a few questions here I took a coolant sensor, a TPS and a coil with me. TPS and Coil went in first and it did run better, but as soon as it warmed up it went full rich and died. I added the coolant temp sensor, disconnected the batt to clear codes, reconnected and it fired right up and ran better than ever.

The CEL light went out, and a couple of days later it went through E-testing with flying colors. I think the seller is still scratching his head...:haha:

Rene
 
I had a complete TBI 350 sitting on the garage floor that I drove home, it was out of my Crew Cab. For me I just robbed a few sensors and spent about 10 minutes swapping them into the 90.

The funny part was looking around inside the '90 I saw a Q-jet and older HEI distributor sitting on the floor in the back. It was pretty apparent the previous owner was so frustrated he was about to swap to a carb...yet thanks to CK5 I had it running perfectly in less than 10 minutes, then drove it 40 miles home. :D

Rene
 
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