Disco Keeps Dying
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Disco Keeps Dying
jkid
4/23/2008 5:26:17 PM
Hey guys. I installed my new MAF today after getting the PO734, PO171, PO174 codes for a while. My son then took it on a short trip and about 5 miles later it died on him. He was low on gas, so we figured he just ran out. We put in a gallon or so and a short while later it wouldn't start when he filled up at the gas station, I figured maybe he got air in the line on the way there. Then when it died a mile or so later I put the old MAF back in. 5 miles later it dies again and with a little bit of cranking it starts up again and we made it home. I got codes PO734 twice (once with PO171 and PO174) and then the last time I got just PO171 and PO174 with the old MAF back on.
Can a bad/wrong MAF keep causing it to die and be hard to start again (like it had no fuel). It seems more likely that the fuel pump might have been toasted when he ran it dry, but I'm not sure if it would work intermitantly again or if it would throw those codes? It look a lot of cycling the ignition/starter on and off to get it going each time, but once it caught it was fine. The timing of it seems like the MAF but it could just be a coincidence. Any ideas?
Disco Mike
4/23/2008 5:34:23 PM
No, it won't cause the engine to stall.
Possible crank sensor, is your drivers side v/c gasket leaking oil?
jkid
4/23/2008 5:37:53 PM
My drivers side v/c does seep a bit of oil, yes. Not enough to get to the ground, but def. seeps. Is the crank sensor right below that?
jkid
4/23/2008 5:58:42 PM
I went outside and looked. I looks like the sensor is just below the exhaust manifold with a heat shield over it?? The wire down delow is covered in oil, but the sensor is actually really clean.
Should I be able to hear the fuel pump turn on with the ignition? I listened for it through the filler neck one of those times it died, but I didn't hear anything.
jkid
4/26/2008 7:52:10 AM
^^ I was looking at the knock sensor.
Anyways, I haven't had a chance to test anything yet other than yesterday when I started it up to see what exactly what it was doing. Basically, I runs for about 10 minutes, than shuts right off, no sputtering or anything. Before I tested the fuel/spark/vacuum or anything, I decided to pull the crank sensor out while the exhaust was still cold. Last time I saw a magnetic sensor like this covered in metal shavings it didn't work. Is this most likely bad? It seems like electronics start to show their problems when they get hot and that is when the truck decides to shut off. No codes by the way.
Spike555
4/26/2008 8:27:01 AM
I would suggest the fuel pump. It is weak and cannot provide a sufficient fuel flow to keep it running.
After it quits running check the fuel pressure. I think that you can put a fuel pressure gauge on it and check it while it is running and then see if the psi drops off while it is running.
jkid
4/26/2008 9:26:34 AM
I'll try the fuel pressure next, but I can't find a valve to hook a guage up to. The RAVE seems to show a schrader valve behind the engine somewhere but I don't see anything, it's pretty tight back there.
I cleaned the crank sensor off and the truck ran for about 20 minutes now rather than the usual 10 before it quit. It wouldn't start again and I found that there is no spark. Does the sensor control both injectors and spark?
roverguy7
4/26/2008 12:02:04 PM
crank sensor only controls the spark, cam sensor takes care of the injectors. when it dies, does it just crank when you try to restart? if so, does your check engine light go off when youre cranking?
jkid
4/27/2008 12:08:54 PM
It just quits after 15 minutes of idling. It cranks over fast when you try to restart it, there just doesn't appear to be any spark. The service engine soon light stays on when cranking. I've gone through this about four times just sitting in the garage and it has not given me any codes. BTW the o ring that seals the MAF at the airbox was missing, that couldn't have helped my MAF any.
Spike555
4/27/2008 12:16:34 PM
OK, try this. Let it run until it quits. Remove the air intake tubing from the throttlebody, have someone crank it over while you spary carb cleaner into the t-body, if it runs then you have spark just no fuel.
That is how one of my customers drives cars that have bad fuel pumps into the shop, his helper drives the car while he sprays carb cleaner into the engine.
I am still betting that you have a lack of fuel.
The CEL will be on while you crank, that is normal.
A fast crank usually means no fuel, if there is nothing to compress in the cylinder then there is no resitance to the piston which means less work for the starter which means it will turn over faster.
jkid
4/27/2008 12:36:18 PM
Good idea, I meant to try that.... Nope, sprayed starter fluid into the throttle body. Nice fast crank, but no ignition. I'll most likely just order a crank sensor on Mon. Seems like a good preventive measure even if it's not the problem, but it sure seems like it!
Spike555
4/27/2008 12:39:00 PM
Well, it was worth a shot.
roverguy7
4/27/2008 8:09:23 PM
its youre crank sensor. the check engine light will extinguish once the ECM receives a good signal from the crank sensor, hence if it stays on when it wont start, the sensor is bad, or at least the connection to it is.
jkid
4/28/2008 3:18:44 PM
Well, the dealer had 1 crankshaft sensor in stock today. I swapped it in and let the truck idle for 30 minutes before I was satisfied and shut it off. Until it tells me otherwise, I'm calling it fixed. Between the metal shavings on the sensor, the rust and the burnt looking housing I think the old sensor was pretty well shot. While I was waiting I topped off the coolant bottle and looked for leaks. I found it leaking from the throttle body and down onto the valve cover. I've been trying to keep it topped off for the last month or so. So lets see, the coolant leaks onto the valve cover, pools up and runs down to the back of the engine and drips down onto the crank sensor causing it to fail. Far fetched, but maybe! What bad timing with the MAF replacement though, I hate coincidences. I wonder if my cranksensor could have been giving me my codes afterall?
