I have a 93 Fire-chicken LT-1 A4 that is pissing me off. Okay quick basics - No opti (delteq conversion), full exhaust, Arizona CAI, broken engine temp sensor (read on you will understand). And no it's not the common "opti misfire", as I stated above I have the Delteq ignition system.

The Problem: The car starts up everytime when cold, and will run for about 10-15 minutes. After that point all hell breaks loose. Random loud *** knocks in the motor, sounds a little like misfiring/ blowing the hell up. Tach will jump around like crazy only if I touch the gas, which will also make the knocks worse. Then the motor will hiss as if it had lost all vacume and about 5 seconds later will die. If i let the car sit for approx. 10-15 min it will start up fine and run for another 10-15. Plugs, wires, and coils are fine. All vac lines are connected.
Note: One of the times this happened the motor died, however, there was an extremely loud backfire, that didn't really sound like a backfire. It was loud enough that my friend following me home, 2 cars behind me hear it, with all the windows up and music blasting.

Attempted fix's
1. It was 1k miles over due for an oil change, thought it could be a bad filter so i changed it. not results.
2. Thought it could have been bad gas. So I tried drygas and still have the same issue.

Possible issues I thought of:
1. Could it be a problem with the cooling system, stuck thermostat, or dead water pump?
2. Could it be a bad fuel filter or a dying fuel pump, or bad fuel injectors?
3. I used Seafoam about a week ago in the brake booster vac line. I heard that some people with high mileage have had issues with Seafoam eating away at gaskets, rings, and such. Anyone have any more information on this.
4. The car began leaking oil onto the driveway a bit ago and I have identified the leak as a rear main seal leak.
5. Could the Opti sensor inside the opti-spark, though not being utilized, cause a problem as bad as this?
6. Last possible issue. The motor is just tired and old and needs to be rebuilt.

If anyone has any ideas as to what it could be or could elaborate on any of the above issues that would be great.
There is a possibility that I omitted some information, if I did ill edit the post when I get home later since I'm at work.

Thanks

 

Which engine temp sensor is broken? The one for the gauge or the one for the PCM? If it is the one that feeds the PCM, then the computer does not know that the engine is warm so it continues to richen the fuel mixture which would explain why it runs good cold but when it warms up dies and sometimes backfires could be from loading up the cylinders due to the rich mixture. The timing could also be causing the knock...spark knock maybe???

 

Replace o2 sensors and see if that fixes it. And get a new coolant temp sensor if you say it's broken. Depending on which temp sensor is broken (1 of 2), it's gonna run pig rich and cause issues.

 

Have you scanned the car to see what that turns up? I don't know what would be causing the issues that you have, but that might point you in the right direction.

 

The odd thing is the car is not throwing any codes. The temp sensor thats broken is the one that feeds to the gauge. Could it also be the opti sensor went bad throwing the timing way off. So when the car switches to closed loop its reading that theres an error with the sensor and shuts down the motor... The bad timing would explain the tach freakin out and the backfires.

either way im going to fix the temp sensor tomorrow. If that doesnt solve the issue im going to replace 02's and if i still see no results im going to replace the opti sensor.

Thanks for the help ill stay updated. if anyone else has any other ideas please feel free to share.

 

1) If you have headers, I'd say it's clacking on the frame and causing false knock and your knock module or sensor is gone hay-wire and it's not working right
2) Same as above, minus headers, knock sensor/module have gone nuts
3) Temp, IAT and/or O2s have taken a crap and causing the ECM to think things are way off from what they are. Probably a combination of sensors dead.
4) The EPROM is dead and going into closed loop triggers the use of it and the ECM is getting all sorts of wrong signals and doesn't know how to process them.
5) (not too sure about this one) The ECM itself is dead and is giving bad commands to the fuel injection.

 

did you ever figure out the problem cause the same thing is going on with my car right now, and I honestly think its the opti, car wouldn;t start, put in a new opti, had a coolant line blow getting the opti all wet now it runs great for 10 minutes and then does exactly what your explaining, if the opti doesn't fix it im going to burn it to the ground, the motor that is...and put an ls1 in it...lol

 

Dido!!! Check my thread: Sh!!did I just kill my LT1??? I have been going through this same **** for weeks, but I haven't even got to drive the damn thing yet. I am almost positive it is the opti!! My problems sound exactly the same and I am pretty sure my fan is coming on so it isn't the Water temp sensors. Tried plugs twice (fouls them), wires, fuel regulator, checked the injectors all 3 ways, replaced the IAC, checked for ref signals, ohmed wires, cleaned the throttle body, new ICM, New coil, spacer mod, checked for vacuum leaks a hundred times. It runs good until it is warm, sometimes, and then it is a crap shoot. Boys I think we are going to have to face the opti head on, unless there are any more ideas.!

 

i just ordered my opti im praying this time... if its the opti I'm going to hopefully get the mods to made a sticky out of this or make a new thread because it seems like a lot of people are having this same problem...

 

Well i guess this is prime time when opti's like to hate there owners. Mine is also doing the same ****... once it warms up it will backfire and the tach is all over the place. Checked my coil and module and there fine so it had to be the opti as i was loosing injector pulse and spark. It did this for a couple tries and then eventually just wouldnt start at all. Pulled the cap and rotor off and i had alot of corrosion inside and on the optical sensor so it was done. Had a used one from a buddy of mine i said what the hell and try it out. Swapped it in and made no difference at all. So i was quite pissed earlier putting a used good opti in and its still not fixed. I ordered up a brand new opti and brand new cap and rotor. Started right up and no issues so i shut it down as i didnt it fully back together. I was happy for the moment so i left it alone and ill be going back at it tomorrow to get it back together see where im at.

 

Would follow these steps first, definitely some of my first thoughts and some i didn't think of

 

So to rule the knock sensor can I just unplug it? Wouldn't it act up on warm up too if that was the case? Can the knock sensor really change enough to not allow the car to start?

Sorry, I don't know how to make this a link maybe someone can help, but I found it tooling around if you read all the way through there is a great explanation of o2 sensors and how to test them instead of blindly replacing them. Worth a look http://www.afbforums.com/forum/index...howtopic=25170

 

That is cool! It makes it a link automatically.

 

Come drop the car off at my house i will have it running in a couple days.

 

let me drive across country for that with a car that doesn't run

 

To answer the questions. You CAN unplug the knock sensor and nothing should happen. What I believe will happen (can't say for sure) is that unplugging the Knock Sensor will basically tell the computer there is no knock occurring, and so no timing will be pulled. I don't know what year car you have Crooked, but if you have headers and they are clacking against stuff, you have the option to upgrade the knock module inside your computer, to the 96 Vette with the LT4, it's less sensitive. Us people with 93's can't do that, I mean I'm sure if we ripped the casing apart on the PCM's module, it would look like ours and we'd just have to solder it in place of ours, but that's just a theory as I don't have a 94+ knock module to tear open If anyone DOES have one, and doesn't need it, let me know cuz I'd like some pics of the thing with the plastic casing tore off

 

Thanks Formula 350, can't you also desensitize the knock count through tuning? I had a mail order tune done ($361 I think I might have got hosed), but they did not give a print out so I have no idea if they changed it. Would the knock sensor pull out enough timing to to not allow the engine to start when warm though? Well, it will start with the pedal to the floor and then miss and blow black smoke and dies if I lift, let it cool down for a night, go out fires right up, runs good (as many times as you want) until it is warm....then it all goes to crap...hopefully not opticrap, but I picked up a new one today because I think it will come down to that.

 

Well, I don't think it's with in the capabilities of the system to pull that much timing that it wouldn't make it start BUT it might be dumping far too much fuel since it's in closed loop (whatever warm is, I can never get that right lol). I still think IAT or O2s. They're cheaper and quicker to do than an Opti anyways.

And yes you can desensitize the KS via tune. I'm sure who ever did your tune has a file on what was done to yours, just email them. That LT4 Knock Module does just that, just not directly through tuning.

 

any codes?? sorry forgot to ask??

 

well if the problem is with your header banging and it detecting that much knock then the only solution is clearance the header or whatever is banging, or remove the knock sensor all together, which i wouldn't particularly advise to everyone. If its that much knock then desensitizing it through tuning, or an LT4 module will not solve the issue, thats much more knock. They are for rockers which clank a little, not that much noise. But yes you can pull the knock module and it just simply will not pull timing or detect knock.