fuel pump relay or cam sensor

windpirate · Post by **windpirate** » 04 Oct 2011, 16:27

Hi folks... after a bunch of testing, I am at an impasse...How do I determine if my fuel sensor relay is bad or if my cam sensor is the problem? The car stalled suddenly and wouldn't start again , I've ruled out the fuel fump and fuel filter, and I appear to have spark. Thanks for any help in advance. Brian

Post by **erikv11** » 04 Oct 2011, 16:48

If you are not sure about the fuel pump relay, here is a copy-paste of a previous reply by Ozark Lee:

Try jumpering the fuel pump relay and see how it behaves. The relays start to get intermittent when they begin to fail. To jumper the relay out of the system remove relay 103 from under the fuse box cover. On the bottom of relay 103, molded into the plastic next to the terminals, are numbers 31, 31b, 15, and 87. Put the jumper wire between the socket positions associated with pins 15 and 87.

However, in your post do you mean the car has fuel pressure at the rail? If that is the case then there is no issue with fuel supply, relays are doing their job. Move on to looking at cam or crank sensor. Sorry I don't know how to troubleshoot those ...

windpirate · Post by **windpirate** » 04 Oct 2011, 17:04

Thanks It appears I do have fuel at the rail. I read the codes. And they were P0172,p0171, and p0422. I'm not sure what this is telling me.

Post by **erikv11** » 04 Oct 2011, 22:18

p0171 fuel mixture too lean
p0172 fuel mixture too rich
p0422 O2 sensor or catalytic converter

Possibilities:
- bad MAF sensor. Test this by unplugging it, see if the car runs. Note this may set additional codes.
- bad front O2 sensor. Seems unlikely.
- bad ECT sensor, the little brass unit that plugs in at the coolant thermostat, the ECT has 2 wires coming out if it. If the wires look scaly or like there is coolant coming out there, then it is likely bad. They definitely go bad, if it has never been changed I might try that. Can you get a used one from the junkyard and try swapping it in?

ECT actually seems the best bet of the ideas I list here, because p0172 and p0171 are "opposite" codes as if a sensor is really malfunctioning not just broken.

windpirate · Post by **windpirate** » 08 Oct 2011, 09:37

well I gambled a bit and put a new Cam sensor on it.... it still doesn't run. How does the fuel relay and the coolant sensor figure in. Will it not start if the temp sensor is bad? How much pressure should I have on the fuel rail?

Post by **erikv11** » 08 Oct 2011, 11:13

The ECT (coolant sensor) tells the ECU what the temperature is, then the ECU tells the engine where to put the air:fuel ratios. If the ECT is giving screwy signals (which is common when they fail) then the engine gets all kinds of wrong information at the ECU, and can run both too rich and too lean. That explains the weird thing about your codes, that you are seeing codes for both too rich and too lean. And too rich can give that p0422 code, too. That wold explain all of your codes. Yes a bad ECT can lead to no-start. It can lead to all kinds of bizarre engine behavior so a good possibility.

The fuel pump relay doesn't really explain the codes, it is just a common cause of no-start. But if you have fuel pressure at the Schrader valve on the fuel rail, when the car is on, likely that relay is OK. Fuel pressure is supposed to be like 40 psi I tihnk - do some searching it has been posted about recently on this forum.

Is it possible the codes were already there from before, or did they show up when it went into no-start?

The other common no-start is the crank sensor.

Here is what I would check, in this order:
(1) spark. Do all of your plugs spark? pull each boot and see if they spark to the head when you crank it.
(2) fuel. I tihnk you checked this already.
(3) compression. maybe not likely but keep this in mind - is it possible the car is simply flooded? search "lawn mower syndrome" on this forum. Do a compression check if you have a gauge.
(4) unplug the MAF, try to start it. There is no harm in this, it will tell you immediately if the MAF was the problem.
(5) get an ECT from the junkyard and swap them. If you can't get one send me a PM I can mail you a used one on Monday for cheap. But then you have to wait to check it out.
(6) crank sensor, again I would go with one from the junkyard for troubleshooting purposes.
(7) back to the drawing board.

windpirate · Post by **windpirate** » 08 Oct 2011, 11:57

Erik - thanks...It is totally possible the codes were there from before. I just put a brand new cam sensor...thatts different form the crank sensor correct? I changed the ECT last year. Gonna check each plug. and other stuff.

windpirate · Post by **windpirate** » 08 Oct 2011, 12:47

New code 335 ?

Post by **erikv11** » 08 Oct 2011, 12:52

Correct, crank sensor is different, it mounts like into the top of the transmission. Below the distributor.

Where did the ECT come from? If aftermarket, it could be suspect. If Volvo, then likely not the problem. Do you still have the old ECT, did it at least run the car? You could swap it in.

Aha new code, you may be getting somewhere, crank sensor code:

http://www.obd-codes.com/p0335

windpirate · Post by **windpirate** » 08 Oct 2011, 13:16

Thanks again Erik...how can I be sure this is the problem...I'll buy a new one if i'm sure thats the fix. Can I test the one in the car somehow?