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Multiple issues, need help diagnosing 4.7 V8 (1 Viewer)
- Thread starter gthoman
- Start date
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There is no IAC on these motors; the ECU controls the idle via the throttle body.
Random thought: Did you check your throttle body for contamination? There is a cooling circuit that goes through the throttle body that, if broken, leaking, etc could introduce coolant to the engine. Would show trace amounts in exhaust. A new throttle body is WAY cheaper than a new engine. If the leak down and compression tests show good, it could make a hell of a lot of sense. Also, no sensor on that for leaks, so it wouldn't throw a code.
alia176
SILVER Star
I think I horded a throttle body from a wrecked 4.7. I can check if needed. The OP can borrow it to rule out one possibility.
Ahh, thank you for that!
- Thread starter
- #65
Thanks everyone, going to try to do the compression test tonight, don't have a leak down tester, but will see if I can borrow one. Not sure if I will get to it tonight since I'm in the Raleigh, NC and looking like Florence might get closer than I hoped and will need to get all things flyable out of the yard, 
but will keep updating as I find more info....
but will keep updating as I find more info....
stay safe out there!
Glad you got some diagnostic results and sounds like you are headed in the right direction. Compression tests by the way are one of the first diagnostics to perform for many possible problems. That’s why several of us asked about the compression testing as it really fit as a possible. Remember, from the earliest internal combustion engines to the current fancy ones all require the same three things, air, fuel, and spark. As half K said, start with the basics and then narrow to specifics. Low compression can cause a misfire and throw a code as well as poor performance including idle. All that said, I am very curious to see what type of numbers come back from the compression test. As Onefast said, stay safe out there, sounds like a bad storm...
A compression test will be a quick and simple check for most DIY mechanics. The leak down test is by far the better of the two. You can have issues and still get passable compression numbers. With the leak down, if you are getting compression into the water jackets, you will actually see it when you pressure up that cylinder.
I would say all things are pointing to a failed head gasket. The cooling system coming apart is almost a dead giveaway. You now have a positive block test, there's strike two. A compression or leak down will isolate which bank and cylinder/ cylinders. Soon you will be able to come up with a game plan based on some facts. Your on the right track now.
I would say all things are pointing to a failed head gasket. The cooling system coming apart is almost a dead giveaway. You now have a positive block test, there's strike two. A compression or leak down will isolate which bank and cylinder/ cylinders. Soon you will be able to come up with a game plan based on some facts. Your on the right track now.
alia176
SILVER Star
This might be useful to the OP. How does one do a compression check with DBW engines? In the old days, you open up the throttle valve wide open, crank the engine few revs then take the compression gauge reading. Will these DBW engines allow the operator to open the throttle valve wide open while cranking?
Yes, you can hold the throttle body wide open while cranking. An easier way would be to just remove the TB altogether.
- Thread starter
- #71
Finally got some time to do the compression tests. To get the compression test I put the gas pedal to the floor and turned over the car for the count of 5. From what I found, if your standing in front of the car cylinder 1,3,5, and 7 are on the right(driver side) and 2,4,6 and 8 are on the left(passenger side)
cylinder1: 170
cylinder2: 60
cylinder3: 170
cylinder4: 40
cylinder5: 90
cylinder6: 70
cylinder7: 80
cylinder8: 160
Not good...
cylinder1: 170
cylinder2: 60
cylinder3: 170
cylinder4: 40
cylinder5: 90
cylinder6: 70
cylinder7: 80
cylinder8: 160
Not good...
So what do these numbers mean?
Head gasket? Or rebuild pistons and cylinders?
Wow. Both banks??? Did you already verify the timing belt didn't skip?
That's crazy...5 bad cylinders?!
I'm calling it as a timing belt tooth jump or improper install. With numbers that low it would have never run right.
I'm calling it as a timing belt tooth jump or improper install. With numbers that low it would have never run right.
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That's what stands out to me as well. Both sides having issues with numbers that low don't make sense overnight. Not that we have compression numbers prior to install, but still highly suspect of a timing belt issue.
- Thread starter
- #77
I have not double checked the timing belt, but also felt the numbers were off. I'll check the timing belt and get some pictures over the weekend.
alia176
SILVER Star
I concur with others, the low #s are pointing to the valves not fully closed when they should be. Timing does seem to be the prime suspect.
I'm enjoying this troubleshooting experience and learning quite a bit, at the OP's expense unfortunately.
I'm enjoying this troubleshooting experience and learning quite a bit, at the OP's expense unfortunately.
Agree with Dan. Typically when a headgasket goes it might affect 2 or maybe 3 cylinders, but not 5 cylinders and both banks. I am still leaning towards some timing issue.
Could be part of it and interested to see what he finds on the marks. OP states in post 47 that his symptoms are similar to when this whole thing first started. Unfortunately, he still has a positive test for combustion gases in coolant. If timing belt is off, I would still repeat the compression test after proper alignment.
