Background on the vehicle.

209K miles, 54k on a new from GM motor.
New injectors due to plugged poppets
New AC platinum plugs
New wires
New cap
New Distributor (not rebuilt, was set to 0 deg)
New intake gaskets (leaking from lifter valley into cyl 5)
Fuel pump replaced recently with Delphi pump, pressure is excellent @ 66PSI Key on Key off, and 56-58 idling, spike to above 60 with a blip of the throttle.
Has JBA headers, no cats, Gibson exhaust (not that it matters)
No other part has ever been changed other than what was mentioned.

Problem is it has a hesitation at cruise speeds and the idle is slightly rough and does not hesitate when accelerating. It seems like it is cyclical, revs up down while maintaining constant speed. Seems to do it a little more as it warms up. While hooked up to my friends Snap-On Modis scanner it misfires on cyl 5 but is not doing it enough to throw a code. I forget how it does it, but it will misfire up to 16 times per cycle (I am not sure if I have that correct, I just know I saw 16 on the scanner, I have a MT-2500 with no OBDII packs and have never seen this done before)

We checked EGR function, IAC action, MAF readings, TPS, Crank Shaft Poss. Sensor, as well as checked the alternator output just to make sure it wasn't causing any issues. All are fine.

I have not replaced a single part that it was not in need of and refuse to just start throwing parts at it (although that is tempting at times).

I still need to do a compression and a leak down test, but it has headers and will require me removing them in order to gain easy access to the plugs.

I am just wondering if my thinking could be correct on the issue of cyl 5. Seeing as it was eating oil from the intake gasket leaking and fouling the plug. Is it possible that the valves are sticking in this specific cylinder due to the oil consumption? I am just thinking the heat from the valves more specifically exhaust would cause the oil to coak and cause a sticking valve condition. Or is it possible the piston is loaded with carbon/oil mix and is cousing the miss. If this is feasible, is there anything I can do short of a teardown?

Thanks,

:runaround:Chris

I would remove one of the heads and see if its all carboned up...carbon will wear an engine/componets very fast....why all this carbon deposits....something defective ???could be the intake or / blowby gases creating this condition....

I am going through a similar problem with my '98 Tahoe w/189,000 miles. After replacing ignition components, I still have a skip when passing gear is kicked in and it also cranks excessively to start. We have found that I have 3 leaky poppets.

What I have learned about the Central Sequential FI while researching my problem is that this type of system needs proper fuel pressure and volume. If my memory serves me right, you need about 63 lbs minimum to activate the poppets.

I have found a Sequential to multiport kit since due to my mileage, if I replace 3 poppets, others can't be far behind and they add up real quick at $62 apiece !!

Thanks for the replies. I still have not done a leakdown test. I think this will tell me what is going on with it. I am thinking I have valves sticking in the no. 5 cylinder.

Yes, the popets are expensive. If you have an Advance Auto Parts store local to you they carry the conversion injectors at a good price. I think I paid $350 or so.

Once I get around to working on it, I will post my findings.

Chris

Do not rule out camshaft retard setting being way off.
over 4-5 - or + degrees can cause missfires.