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I just had a pro rebuilt engine installed in my 2000 Jeep Wrangler 4.0 automatic. It now shakes and wants to die at idle speed but is 100% perfect at all other RPM ranges and has good power overall.
When coasting down to stop at a stop light it will shake pretty bad and possibly die, it has died 3 times at stops this week.
I am no expert in diagnosis but i`ve spent the past few weeks watching videos and testing everything I can with my laptop scan setup and also my cellphone with OBDWiz or whatever its called. I also have the factory service manual.
Fuel trims at idle are typically around negative 18% – anywhere above idle, even 900 RPM and things go completely normal. Before the new engine it was consistently at 4-6% positive fuel trim. The engine was replaced due to a broken piston skirt.
So my big concern is whether or not this is a coincidence or something worse going on inside the engine. Here is what i`ve tested or swapped from my good running 2000 XJ parts:
- Fuel pressure: 45 PSI, completely within spec according to all procedures in the FSM.
- Cam timing: My scanner just says “in-sync” but i`m waiting on a DRB III to get here so I can fully verify – although I did flip it 180 out and even unplugged it with zero change.
- MAP: Numbers look fine, plugged in a spare known good one with no change
- Coil Rail: Swapped to known good with no change
- Injector balance test: The old Siemens injectors were out of range by about 3 PSI across the group – swapped to rebuilt Bosch 4 holes with no change
- IAC: Was a little dirty, so put in a known good one that is nice and clean, no change
- Vacuum: Unplugged and capped off everything with no change
- o2 Sensors: Discovered one wire that had a bare spot & one with a cracked plug – changed both upstream with new OEM, no change
- Discovered 180 thermostat from shop who did install, put in new 195 and a new temp sensor, no change (now runs at 210~)
- Adjusted throttle valve cable for auto trans
- Replaced new champion plugs with correct Autolite APP985
Things I have not yet done:
Compression test
Verify good cats – the engine runs so well with such good power that I don`t really suspect these
Fully verify cam/crank sync – though I doubt this is an issue, since i`ve messed with these quite a bit and never had these symptoms due to that sensor – i`ve also carefully aligned it all with the toothpick and TDC method, including 180 out. This will be verified soon with a DRB 3Observations:
SInce this is happening on both banks, I believe it must be something external .. like MAP, IAC, IAT, who knows?
On first start up before entering closed loop, there are no symptoms at all
In my mind this is a simple issue of the computer pulling fuel for whatever reason, and thus causing the rough idle and possible stallI am 100% open to testing anything anyone suggests, and following through with the final solution here. A year ago I went through the same thing, except for a random misfire which ended up being a non Mopar crank position sensor, that was a huge relief to discover.
I have driven it pretty hard for a few hundred miles since the new engine – just to break it in and so on.
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[quote=”relative4″ post=195210]Sounds like you may have some leaks in one or more of those places as well. Once you have the main problem fixed and a nice 20-21″ vacuum, I’d reconnect each of those hoses one by one and see what loses you some vacuum. First things first, smoke and compression.[/quote]
Working on finishing my smoke tester next. When I do the compression i`ll also double check that the DIS is precisely in time, as far as you can without the cam-sync function in the DRB 3.
What would the mechanical timing issue look like? Off by a tooth? Others i`ve seen who have been off a bit cant even get their 4.0 engine started.
Compression test results: 135 to 150 psi across the 6 cylinders.
Was not able to verify mechanical timing but did reset the DIS again just to be sure everything was exactly in sync with the timing mark on the pulley. No change.
The Jeeps of that vintage are known for developing cracks in both the inlet manifold and in the exhaust manifolds.
You’re seeing negative fuel trims (rich condition) on both banks at idle. Whatever it is, the problem is unlikely to be bank-specific such as leaky injectors.
What happens to fuel trim at higher engine speed? Do long term fuel trims go back toward zero? If so, this would be consistent with a bad fuel pressure regulator. You can check this.
You mentioned fuel pressure was within spec. Was this while the engine was running or with key-on-engine-off? If the latter I would try getting a reading with the engine running.
Specifically, I’d check fuel pressure while the engine is running, both with the regulator vacuum hose attached and without. There should be specs for both states.
Are your readings for both within spec?
[quote=”civvy” post=195266]
Are your readings for both within spec?[/quote]Yes, all fuel numbers are within spec at all driving speeds and ranges.
Today I was able to set the cam sync to spec using the DRBIII – it of course made no change, vacuum is still very low at idle – driveability, vacuum, and fuel trims are excellent under load at all rpm ranges above idle.
Here is a screenshot of the DRB fuel trims – not that it matters. I will be opening up the timing cover this week and seeing if everything lines up. I really don`t know what to think about that .. 1 tooth off is like 13 degrees, that may be excessive for it to run so well.
Also, smoke tested this weekend, could not find any vacuum type leaks anywhere.
I finally got into the engine and pulled the timing cover. I set the harmonic balancer mark to the peg that sticks out of the timing cover, and this is what I found… As far as I can tell this is dead on. Next i`m pulling the valve cover and looking closer at where the cam actually is. I also have a degree wheel setup but this timing set isn`t adjustable. Last resort i`ll set that up and see exactly where we are…
Any other ideas?
Hey, I’m familiar with these cars. I’ve seen timing issues before with them, and that chains looks slightly loose, but nothing I could be concerned with. However The symptoms really indicate internal engine issues. However, if you swapped the engine, did you replace the intake manifold gasket? This is extremely crucial if you didn’t.
Once I pulled the valve cover and turned the engine over by hand, I was able to see that the compression stroke is when the cam is 180 degrees from where the marks line up. In other words, when the marks are lined up we are right at the end of the exhaust valve closing. No idea what that is all about, but I went ahead and redid the DIS timing with a .073″ pin gage lining the pieces up, and stuck it back in .. it ended up being advanced by one tooth (on re-install, meaning it was retarded). All of these are good signs, but i`ll have to wait til tomorrow to button it up and try starting it, then re-setting the timing with the DRB III.
If it still doesn’t work i`ll drop it off at the shop that did the install. My reasons for investigating this rather than making them do it are too long for this thread …
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