thedrewski86

Hey, so I took my 94 p/u to a muffler shop at lunch today to get my new o2 sensor put on. I was going to do the work myself but the bolts were rusted and the studs were mostly broken off so I figured I would have a shop with a welder fix it up.
Figured it would be pretty quick. The dude told me $45 bucks to put it on so I waited during my break. 1-1/2 hrs later they tell me it's done but it won't start! I take a look at it and figure they flooded it after I can't start it. I tell the guy I'll be back after work to pick it up.
I come back and it still won't start. They have no idea what's wrong. I've never had this problem before. Right before my buddy picks me up I tell them to check the fuses. It seems like the engine is starved for fuel since it cranks but only runs for a second so I figure maybe the fuse to the fuel pump blew when they were welding. Is that possible? What else could cause this?
I'm almost ready to cut my losses and have them tow it back to my house so I can fix it (at no charge obviously). I just want to make sure they didn't somehow fry my computer.

James Woods

iTrader: (1)

Check the Efi fuse in the fuse box under the hood, should be 15 or 20 amp fuse. If the O2 sensor wiring is shorted it will blow that fuse and not start.

thedrewski86

Excellent suggestion! I will check that in the morning.

abecedarian

If the EFI fuse is blown, it won't start at all since the ECU won't have voltage to trigger the injectors.

Current from arc welding will take any and every path available to ground. If they welded on it and had the ground electrode clamped in the wrong spot, or welded with the O2 sensor in the bung and plugged in to the harness, it's possible the ECU and/or O2 is damaged since the they could be part of the path to ground. Not saying they did that though....

Maybe try disconnecting the O2 and see if it will start- if it does, the O2 is fried and affecting the ECU. If it doesn't start, any one of dozens of things could be wrong. You could put a jumper between the Fp and B+ terminals in the diagnostic connector to make the fuel pump run and see what happens. If it runs then, the next thing would be to check the circuit opening relay by the ECU.

thedrewski86

Okay, so I'm going to check all the fuses, disconnect the o2 sensor and see if it starts and then check the fuel pump. If the pump runs, what is the procedure for checking the circuit opening relay by the ecu?

I don't know if they welded with the o2 sensor connected but I do know they didn't disconnect my battery cable (which made me nervous). Aren't you supposed to before you weld on a vehicle?!

bone collector

shouldnt the shop have to fix whats wrong with your vehicle since it drove into their shop but wont drive out?? i really hope you get it fixed quickly and easily but arent they responsible for the damages?? if they deny any wrong doing or responsibility im not sure i would take it back there again.. just my .02

thedrewski86

Hey man... NWI! Don't ever go to Amerimex on Kennedy!! I just talked to the dude and he won't fix or tow my truck w/o charging me. They don't know what's wrong with it but they claim this was pre-existing. Total BS since it rode fine before.

Oh well, I've got towing on my insurance so it should be getting dropped off at my house in an hour or so. At least I don't have to pay for the tow, I just wish these guys were paying for it instead of my insurance.

bone collector

Hammond is about an hour n half away from me, but never to far for a yota!! lol hope you get your truck running soon. Document everything, takes lots of pictures and get receipts for parts. then take it back to the shop and demand some compensation or you will turn them into the BBB. I smell a rat there, they screwed up and are trying to get out of it

wyoming9

iTrader: (1)

There are pros and cons about removing the negative battery cable while welding.

I tend to always play safe and disconnect the battery cable. Because sooner or later it will bite you in the butt.

I have found most automotive shops do very poor welding and have really pos welders.

Something is not right you drove the truck to the shop and got it towed home sad fact is there is really no proof you drove the truck there it would be your word against the shop.

Good Luck

thedrewski86

Well it's home now. I'll diagnose it later, busy weekend ya know. My gut tells me fuel pump relay as there is no fuel pressure (it does have gas!!). Even if they did fry my ecu I can get one cheap on fleabay. Good thing I don't need this for a daily driver or I might be getting REALLY pissed at these guys. I already yelled at him and told him he was full of $ hit. Oh well, I would feel better if I stayed cool and just fixed the problem.

bone collector

good plan.. keep us posted

abecedarian

One other thing to consider is the O2 sensor wiring itself. It has 4 wires- two for the heater and two for the signal. If the wires are crossed up, that may be an issue, but that's only if it was one of the universal O2's where you have to cut and re-use the old plug.

meCANic87

it sounds like they have messed up when installing the o2 sensor i bet it was one of those universal ones and they wired it wrong, and not giving signal to the ecm, but when u said their was no fuel pressure that threw me off, that sounds like the weldor grounded out to the chassis and fried the comp or blown a fuse, jump the connectors and see if the fuel pump comes on, check the relay and all the fuses, and take the o2 sensor completly out and see what happeneds, really just a troubleshooting issue, guys at the shop could of done this and i dont see why they didnt, u need a wiring diagram to see if the o2 sensor is wired right, if everything checks out, i would get an o2 sensor with the adapter not the universal ones where u have to splice the wires, and install that yourself it really easy, if that doesnt work then your comp is fried

thedrewski86

I bought the o2 sensor myself and it is the 4 wire one. I already tried to start w/o the sensor hooked up with no luck. I did try to jump the terminals to make the fuel pump run and it won't run, this is what makes me think it's a relay or fuse or something. Hopefully I can check it out tomorrow after work.

jerry507

As far as I know the O2 sensor isn't even used by the computer until the temperature comes up to the point where the engine can run closed loop. The voltage from the O2 sensor doesn't even make sense until they heat up; they just read min.

Obviously check the wiring for the O2 sensor, but given that you can run without one entirely I doubt that is specifically the issue. Disconnect it just to be sure.

If you can't get past cranking, you either have no spark or no fuel. Excluding a wiring issue, you can check the fuel pump voltage from the diagnostic connector. You can draw a spark from the main high voltage wire to the engine block during cranking to test for spark. One of those will yield a starting point I bet.

thedrewski86

Just got a chance to look at my truck. My place to start was going to be my fuel pump relay (after searching other threads). Please tell me if my reasoning is sound here:

I jumped the Fp and B+ terminals in my diagnosis box and turned on the ign. I didn't hear the fuel pump come on. Tried to start, obviously it didn't start.

From other threads I thought the next step was relay (after fuses which I couldn't find any damaged). Now, the fuel pump relay is directly above the ecu behind the passenger speaker right? I found a 12v relay up there above a 20 amp and 10 amp pair of fuses that said "heater". I've got the thing out and it looks good. I checked continuity on the terminals and got it with one of the two large flat ones on the bottom and the thin middle one on top. I have no idea what that tells me.

What next? Somewhere I'm not getting power to my fuel pump and I hope this is step 1 in checking it out.

Crap, is it the efi main relay I'm looking for in the engine comp fuse panel?? When I turn on the ign I can't hear it clicking...

myyota

Did you check the fuses with a meter ?, sometimes a fuse can look good but be bad. Try unplugging the wiring harness at the fuel pump, hook up a meter and turn the engine over and see if you get power to the fuel pump, if you do then the fuel pump is bad. If no power to the fuel then the problem could be the AFM or the cor relay.

thedrewski86

Just checked the fuse w/ my voltmeter, it's good. I doubt the fuel pump is bad since this all started when this mechanic started welding on my truck. Because of that I think it's something electrical... could that have actually done something to the pump itself?

Also, where is the wiring harness? I looked around, is it on top of the tank?

thedrewski86

Is this the one you're talking about?

myyota

The wiring harness should run along the frame to the top of the tank and plug into the fuel pump. That could be it, did it looki like it plugged in around the sending unit ?.

Considering all the late model vehicles with all the electronics that they have that have exhaust work done on them with no problems, I think that what has happened to your truck is just a coincidence.

Keep checking and let us know what you find.