I've put about 200 miles on my new 3mm apex seal, street ported motor. It is very difficult to start, particularly warm start. In fact it only starts with the throttle slightly depressed when cranking. Also, idle is very lumpy. The shop's explanation is that the motor needs 500 miles before it can achieve optimum compression. Is this for real?

 

whoa waltk88, i am haivng the exact same issue w/ my freshly rebuilt and ported motor... i've got about 250 miles on mine, 2mm seals but w/ a pretty aggressive street-port, and mine cranks up fine when it is cold but after getting hot from some driving it is much harder to start, and the idle is *really* low... i have to force gas into it to keep it going at some points, and have had problems w/ it dying altogether at traffic lights... i am worried as hell.

 

Anyone have any wisdom on this issue?

 

double-bump from me too... very fearful of my FD's health..!

 

From the symptoms described I would say that both the engines are suffering 'LOW COMPRESSION' which is definately not good if the engines were just rebuilt. Yes, it is true that during the first miles of a new rebuild, the compression is slightly lower, but that doesn't mean that it doesn't start when hot. It usually takes aprox. 500-1000 miles before you gain the max compression for the engine, due to all the seals "sitting" to their respective faces. It could be something else, but from past experience I am forced to believe that this is the cause of both your problems. Good Luck!

 

wow, terribly distressing thing to hear... would my vacuum level give any indication in either direction? when the car is idling normal (around 1000-1100rpm) the vacuum sits around 450-470... i was under the impression that this was a good sign w/ a new engine. whne the idle starts to dip out (about 580-800rpm) the vacuum sits at around 340-380. another thing i noticed today was that if i sit a while after my warm start, the idle will eventually level out back to its normal range... seems to take like 5-10 minutes though before it corrects itself. could this be related to me not having an air-pump any longer? this motor has 320 miles on it as of today, and i'm hoping for thousands more..!

 

Who rebuilt you guys motors??

 

Is it a Hayes Engine by chance?

 

Have you ever heard how a V8 with a wild cam idles? You are having the same type of problem. Low idle compression and high intake/exhaust overlap. Depending on your ECU, you might be able to alter idle igntion timing and fuel for optimum control. Then also adjust the idle air control with those two adjustments.

 

I have a Power FC. Can I mess with it to take care of the low idle compression?

 

i've got a Haltech E6k installed, but am running a fairly generic program as i have to break in the motor for 1500 miles... would the ignition idle setting have this effect, where there was a great disparity between the cold and warm idle?

 

I also have the PFC, you can not change the basic idle timing with this unit, not even with the maps, but you can change some other factors.

Idle O2 sensor control off or on, on runs leaner than with it off.
Idle timing control off and on(slightly varies timing for smoother operation).
Water temperature adjustment for additional fuel for warmup idle and acceleration. Also under here is additional fuel for cranking when cold.
Fuel map cells for P1 - P5 for N1 - N3.

You might also try minor changes to the primary injector timing.
Idle is also better with a hose going from the turbo outlet to the intake manifold pipe for the primay injector air bleed sockets. That was the original larger hose from the "Y" pipe outlet.