Rough Idle after Engine Rebuild, No CEL

[duke16]

I've just had my engine rebuilt and now I'm getting a strange idle issue. The revs will bounce up and down from around 800-500. Also, the engine seems a little harder to start. It also seems like there is a lack of power, but that could be in my head. What kind of things could cause this without bringing up the check engine light?

Is it possible to get any diagnostic codes without a CEL?

I know there are tons of threads on rough idles, and I've found many possible culprits (for instance IAC, fuel pump pressure, injectors, coil pack), but I'm looking for something that may have happened when reinstalling the engine (and that also doesn't produce a CEL).

Thanks.

 

[duke16]

Turned out the place that installed the engine either didn't time it or timed it incorrectly. So apparently, bad timing will not cause a CEL.

 

[ThePhoenix]

i thought it was electronic timing on our expy's

 

[duke16]

Wouldn't that still need to be set though?

 

[Turdle]

Wouldn't that still need to be set though?

Nope-
But they "might" have had the cam position sensor out of synch-

The ignition timing is controlled by a fixed position sensor-feeding a signal to the PCM
the only way to adjust ignition timing is through a reflash of the PCM ( tuning)

 

[wolfnutts]

is their only one way to put on his timing chain j-t ?? could that be outa whack a tooth or some thing ive not seen the inside of a more modern v-8

 

[Turdle]

is their only one way to put on his timing chain j-t ?? could that be outa whack a tooth or some thing ive not seen the inside of a more modern v-8

If they rebuilt the engine-they would have installed a new timing chain-yes.
If they installed the timing chain mis timed-they are idiots. However-it would have taken quite a bit of time to fix this-
I'm assuming they had the firing order wrong.

 

[duke16]

Nope-
But they "might" have had the cam position sensor out of synch-

The ignition timing is controlled by a fixed position sensor-feeding a signal to the PCM
the only way to adjust ignition timing is through a reflash of the PCM ( tuning)

Well that's interesting...how do you "sync" the cam position sensor?

 

[duke16]

If they rebuilt the engine-they would have installed a new timing chain-yes.
If they installed the timing chain mis timed-they are idiots. However-it would have taken quite a bit of time to fix this-
I'm assuming they had the firing order wrong.

Well it was actually two different people. The guy who rebuilt the engine I trust (Bill's Speed Shop for anyone in the Raleigh, NC area), he did put a new timing chain on and I have no doubt he did it right.

Now the guy that installed it, that's another story. His guys left header bolts loose, and routed the spark plugs wires so that they melted on the headers(which he wouldn't refund the money for because I re-routed them myself, and that voided his warranty).

If the firing order was wrong, would I have noticed that while driving? Because it felt fine during normal operation, it was only when the truck was idling that things were all out of whack.

 

[Turdle]

Ask them how they adjusted the "timing"

 

[aldive]

Turned out the place that installed the engine either didn't time it or timed it incorrectly. So apparently, bad timing will not cause a CEL.

They couldn't time it; timing is controlled via the PCM.

 

[MadExplorer93]

Did you replace the spark plug wires that were melted?

If so, then it could be a fuel filter issue or weak fuel pump.

ALSO: The IAC could be dirty and the MAF too or either one.

 

[duke16]

Did you replace the spark plug wires that were melted?

If so, then it could be a fuel filter issue or weak fuel pump.

ALSO: The IAC could be dirty and the MAF too or either one.

It was doing it prior to melting a wire. Replaced the fuel filter, doubt it was the pump otherwise he would have said so.

Cleaned MAF, had no effect.

I'll give him a call when he gets back from lunch, now I'm really curious as to what he did to solve it.

 

[aldive]

It was doing it prior to melting a wire. Replaced the fuel filter, doubt it was the pump otherwise he would have said so.

Did you check the fuel pressure?

 

[duke16]

Did you check the fuel pressure?

No, but like I said.. if it was a fuel problem he would have said so when he fixed it.

 

[aldive]

You sure have a lot of confidence in "your mechanic".

Good luck ....

 

[duke16]

You sure have a lot of confidence in "your mechanic".

Good luck ....

It's nothing to do with confidence, it's money. If it was fuel related then he would have charged me for the fix, he did not. Whatever the solution was to the idle, it was included in the initial price he charged to do the engine install.

 

[MadExplorer93]

The mechanic without testing fuel pressure would not know if it was a fuel pressure issue which can translate into a weak fuel pump, yeah the pump will pump gas, but at how much pressure?

Also such a surge can be caused by a weak pump or clogged fuel pump filter the filter on the pump.

The surging can also be a fuel rail gasket leaking or damaged or the plenum gasket leaking or damaged, maybe the bolts and nuts need to be retorqued since it is a rebulit engine.

It can also be a plugged fuel RETURN pressure line.

It can also be a vaccum leak, a line leaking in air or the throttle body gasket is leaking or damaged ... so many things can cause this to stall and idle rough.

We here on the forum can only diagnose to what can cause such an issue.

 

[duke16]

We here on the forum can only diagnose to what can cause such an issue.

Yes I know, and I appropriate it. But like I said, I know it wasn't fuel related.

I just gave him a call, and he said the cam position sensor was out a few degrees. So I guess it was minor enough as to not produce a CEL, yet enough to make the idle really bad.