Can no 02 sensor cause the pcm to fry?

 

There is the distant possibility the heater circuit could short to the signal circuit, but extremely rare.

Why?

 

I built the engine in my truck and it has fried 2 pcms. Given they were used and not the original ones. The one that was originally in it came out of an f350 dump. I have a 92 f150 4x4, 351w e40d. But it fried that computer and I didnt want to spend extra money on a new one so I had one from a 96 f150 with the 5.8. It was 2wd but the computer matched an e40d transmission too. It fried that one after about a week of breaking the engine in. So now I bought one with the numbers that matched the vin and calibration code and i am scared it will fry this one too. And the only thing wrong with it right now is theres no 02 connected because I have no put exhaust on it yet, just open headers. I just put it in tonight and it's getting exhaust done tomorrow. It is my senior project for school and I dont graduate if I dont have it finished. I have to present it in 2 weeks and i want to make sure theres nothing else that could be frying my computer. I put a bigger cam in it, I called comp cams and got a cam that is compatible with my computer. Deleted the smog system. Put some resistors on the plugs for the vacuum sensors that matched the voltage the sensors would give to the computer, to keep it from throwing a code. Which before the computer fried it didnt throw a code for those. Also deleted egr, but I plugged the vacuum lines, and I bought a good rated simulator to fit the plug, which i dont remember it throwing a code for that either. The only codes the computers were throwing was transmission not detecting park, which i know why that is, put a new detent cable on it and havent completely adjusted it out yet. And o2. So I am curious if not having an o2 would somehow backtrack into the pcm.

 

Not sure why not having an o2 sensor would "fry" the PCM. I didn't use one for a bit, also open headers, and didn't have any problems. The PCM out of the '96 F-150 should have been OBD-2, so almost no way your truck would have run very well, if at all, without a lot of repinning and major modification of the wiring harness. How did the truck run with that computer?

 

it ran just fine it was an obd1 computer. Same 60 prong connection and everything. I think some of those trucks had it and some didnt. I'm not sure. But it ran just fin up until it fried. It fried while I was driving it. But i still drove it home, 25 miles an hour on the bypass, but it got home. I just dont know what would be causing it to fry like that. I opened them up and the resistors were burnt or looked like they had been leaking. But the one out of the 96 was in perfect condition. Truck had low miles on it.

 

Check the voltage at the battery with the engine running at idle and again at ~2000 RPM. High output voltage will fry electronics including the PCM. So can an alternator with a bad diode. Causes a lot of ripple in the output.

If that tests out good then you need to verify you have those resistors wired in properly and the correct value.

 

a hair over 14. I ordered 75ohm 5 watt resistors. And that's what's on it I tested it before I put them on. Those sensors require at least a 5 watt feedback I believe. I got the exhaust done yesterday. O2 put in. And it is running pretty decent. But it was running decent before I did that. Also it seems like its sending fuel out the exhaust. Still running pretty rich.

 

On occasion i have heard of the solenoid pack in the E4OD shorting internally and killing the PCM. Something else to look at beside the O2 sensors if they check out ok

 

5 watts is a power rating, the 75 ohms is the impedance of the TAB and TAD solenoids. That is what the computer is looking for. Ensure those resistors are insulated so they do not short to ground.


Did we ever get the full specifications of the cam you installed? Too little LSA can/will throw off the computer.

 

 

The specifications look compatible with Speed Density so that's a good thing. Now that you have the O2 sensor hooked up and measuring real O2 content in the exhaust I would suggest to reset the computer by removing a battery cable for a few minutes, if you have not done so already.

If the exhaust still smells rich I suggest to check the fuel pressure and inspect the fuel pressure regulator for signs of fuel in the vacuum port. A leaking FPR diaphragm allows unmetered fuel into the intake.

 

I have reset the computer and checked the fpr. The fpr is new too. But it is using alot of gas and running pretty rich. Also it will backfire a little when its idling. Not when I'm driving if I'm going down a hill and let off or anything. Only when it is sitting and idling or if I stop at a red light. Doesnt do it all the time either its random.

 

New does not necessarily mean good. It's sad we cannot trust new parts anymore. Test and verify is your best ally.

 

not smelling any fuel on the vacuum line on fpr. Check engine isnt on. Just checked the timing. Running good fuel. Iac is working. Map is working too I believe. Checked plug wires they seem good. I'm gunna pull plugs and make sure they arent fouled. Because it's running way too rich and using way too much gas. I've used about 2 tanks in 2 days.

 

Please define that statement


How do you know?


Good idea to inspect the plugs. Depending on city versus highway driving and other factors (very short trips) fuel consumption may not be out of line.