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94 tbi issues.

C

chulisohombre

1/2 ton status
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Apr 11, 2002
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Location
Bangor,Pa
Having a issue guys. Seems like the engine is not advancing on throttle. Replaced map and tps. Knock sensor was broken so replaced that too. Any more than quarter throttle it wants to die open loop it runs awesome if I restart the engine. About a minute later starts to die again when it hits closed loop again. I'm going to get a aldl cable next and see what that says. But anything else I can look at. Egr tests good and fixed vacuum leaks I had. Injector pulse good and new fuel pump and tank few months ago as well as filter. Any help I'd appreciate it.
 
Yep tps is putting out correct voltage. I got some codes now. Showing iac circuit and map to high voltage. May still be from before I replaced it. Tried to reset computer but its still there. Have one bad sensor temp. So going to replace that next paycheck. Don't know if that the cause of it or not. It's broken off so no signal to ECM. Didnt notice til i was checking the wiring for shorts. Also code for lean oxygen sensor reading.
 
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Just the other day I had a 94 tbi that would start hard and cut out hard as soon as you touched the gas. Ended up being the temp sensor
 
Yeah temp sensor is on the list. I don't think the iac is working either. Is there a clear way to tell if its dead? I I just unplug it nothing really changes.
 
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chulisohombre said:
Yep tps is putting out correct voltage. I got some codes now. Showing ias curcuit and map to high voltage. May still be from before I replaced it. Tried to reset computer but its still there. Have one bad sensor temp. So going to replace that next paycheck. Don't know if that the cause of it or not. It's broken off so no signal to ECM. Didnt notice til i was checking the wiring for shorts. Also code for lean oxygen sensor reading.
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If it is the CTS up on the intake by the t-stat housing then I would bet that it being broke off is 99% the cause of the problem. It is most likely dumping way to much fuel into the engine to run.
 
dyeager535 said:
What is IAS?
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Iac sorry fixed it. I was combining the old ics idle control solenoid and the iac together from the old days. Haha. Unplugged iac and not much change. What's it supposed to do When I unplug it? Pulled it out and it was hard to Move the valve itself. Is that normal or should I be able to Collapse it and pull it out fairly easy? So cts will cause those issues? I hot wires it to see if it changed anything and it ran crappier with the two wires connected to the temp sensor. It was the one on the intake. Temp sensor for gauge works ok. The engine just feels like it is stuttering because its not advancing timing To The dizzy. When I shut it off and goes into bypass mode it's running perfect. But for only a minute until bypass ends. I wish I could Just kept It In bypass mode haha. It has all the power I need then.
 
You may have destroyed it. I'm pretty sure you aren't supposed to force those things at all, if anything hook it up while disconnected from the throttle body, turn key to run, let it extend fully.

I've never looked at them closely, but from what I understood, it sounded like it's geared or something like that and you will strip it forcing them to move.

On their own, I don't think they fail. I say that somewhat in jest, everything fails, but they don't seem to be problematic at all...I've never used a new one, so every one I've dealt with is at least 20 years old, with that much use on them. If you aren't supposed to force them, all bets are off. Still "testable" I assume.
 
The cts on the intake is a separate sensor than the one for the gauge, that is in the drivers side head. If it's the same thing I had the cts was shorted and telling the computer the engine temp was like 350 degrees and therefore not giving it nearly enough fuel. If you have an ohm meter it's an easy check.
 
Replace the coolant temp sensor FIRST! Also check the wiring at the plug for the CTS carefully, the wire can break off inside the insulation. Don't waste your time troubleshooting anything else until you're sure the CTS is working.

There's a chart somewhere that shows the resistance vs temperature of the CTS. Maybe somebody here has it.
 
I didn't force the iac to move. It just seemed like it took a lil more force than I though it should. I was reading online blog about cleaning it so I did and it said to collapse it first when putting it back in to reset it so you don't break off the pin if its pushed out too far when reassembling it. Cts will be replaced Monday when I get paid then.so it's a normal resistance sender Much the same as the one on the head for the gauge. It definitely stops putting out fuel somewhat I think. Won't stay running unless I feather the gas like a old carb engine until It warms up. More like retarded timing and can't handle the fuel that's being Dropped until I turn the key off and back on. Then full power is restored. Does the iac reset in bypass mode? Because it idles fine again and runs perfect until closed loop starts. Is it Like a limp mode I'm in now since its Not Getting the right signals? Appreciate the help fellas. Hipefuly fixed on Monday when i get the cts replaced.
 
Some of the codes will trigger limp mode, but IIRC that will be open loop all the time if that's the case. I'm not certain that's true, "limp mode" is a bit of a generic term, and it's more complex (at least with some ECM's/applications) than limp mode being just on or off apparently.

CTS is actually a thermistor as I recall, that's not what the coolant sender is. ECM puts 5V to one wire of the CTS (called the reference voltage, same thing for TPS, MAP, IAT, etc) , and due to the resistance based on temp the sensor is reading off the engine, the voltage going back to the ECM on the second wire will be somewhat less. That difference in voltage is how the ECM "tells" what temperature the engine is running, assuming it's all working correctly. :)
 
What is bypass mode?

It's not your CTS or it would happen when Closed Loop or Open Loop. It's very easy to check CTS.

If you get a CTS error code or suspect it to be bad it can be tested with a multimeter set to OHMS. Here's the readings, it should match the outside tempreture if the engine is cold.

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.
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Have you checked for error codes?
http://coloradok5.com/forums/showthread.php?t=240425

If you think it is timing what is timing at idle? Warmed up should be around 20*. The proper way to set timing is to disconnect bypass wire and set timing to 0*. Then turn off engine and reconnect bypass wire. Also disconnect batt or pull ECM fuse to clear codes because it will set a error code when setting timing. Check for error codes first or they will be lost.

Also disconnecting Batt will loose all stored BLM (Long Term Fuel Trim) data, so it should run better at first. When you go Closed Loop and the ECM is using O2 sensor feedback it is fueling from learned BLM data, in Open Loop it is fueling directly from what is programmed in ECM.. Fuel VE table.

Running bad in Closed Loop is a weird one but how is O2 sensor? This would be a more likely bad sensor then any others with your symptoms!

If it runs so bad in Closed Loop you could just disconnect O2 sensor and run Open Loop always.
 
The cts is broken. The connector snapped off at some point. I had it hot wired to the two prongs on the connector since they were still intact. Just the top of the plug broke off. It ran worse when I had it hooked up. So I know I need a cts. I read that bypass is when you first start it, it will run the ECM codes through the ignition module in bypass or open loop until it reads the sensors and gets a baseline reading. I set the timing a few months ago when I did a full cap rotor and plug change. Ran real good for a couple months and has dropped off since. Pulled plugs and they still look good. I regapped them anyway and put them back in. It was a slow drop in performance and now just can't really be driven without shutting it off and on to reset the computer so it runs Normal every minute. I have the battery unplugged right now and will check codes again when I get home. I tried already to clear codes by pulling the fuse and that didn't work so I'm leaving the battery Off overnight now to see if it will clear. I was hoping you would chime in eagle mark since you are the guru on this stuff. The o2 was showing a lean engine condition. It still seems to be working ok though. I've tried unplugging things one at a time to see if it helps but not a lot of change. It did set up codes for the things I unplugged. Will check that after sitting all night off battery. Hopefully clears some of That since I have replaced some of the sensors. Thanks guys. Seems like I'm at least getting somewhere instead of trying to watch YouTube and reading Blogs on what problems others had and how it was fixed.
 
Couple new things done with it running worse. Put a new cts in and now will barely run. Noticed also coil was shorting on itself. So replaced that. Now it's giving me a code for fuel cal-PAC code52. The exhaust manifold were glowing red when I got to work 3 miles away as well. It will still run semi Ok if I unplug the cts. This is so frustrating. Is it possible the ignition module is dieing after the 30 second initial warmup sequence? Thanks again guys.
 
Manifolds glowing red is a big clue that it is running lean, I wouldn't be looking to hard at the ignition system.
 
What is your fuel pressure? A new pump, tank and filter means nothing if you only have 5 pounds of pressure due to a failed pressure regulator. Unplugging the CTS the engine defaults to -40F which means it pours the fuel in for "cold" operation. Since that is improving it's operation I high suspect you are low on fuel pressure or have fuel delivery issues.
 
^ X2 !

But ignition still needs looked at to make sure timing is set properly!
 
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