I have a rebuilt engine in my Astro van that runs rough when the engine starts cold. When the computer goes into closed loop, the engine runs fine. Any ideas on what to look for? No check engine light on. Thanks.
Doug,
You didn't say what year or injector type (TBI, CPI). Assuming this is a 92 thru 95 VIN "W" CPI (aka CMFI or Vortec) motor, it sounds like the classic problem of the CPI injector leaking fuel past the pressure regulator inside the intake manifold. Sometimes the fuel lines (aka nut kit) under the manifold develop pinhole leaks and cause the same symptoms.
In open loop, the injector pulses are based on a lookup table for air temperature and throttle position. With raw fuel leaking past the pressure regulator and into the manifold, it runs rich. Once the computer goes closed loop, it leans out the injector pulse and all seems OK. It is actually amazing that these things run as well as they do closed loop with raw fuel dribbling everywhere.
Connect a fuel pressure guage to the fuel rail, you should get about
60 PSI with the key on, pump running, and engine off. It should maybe drop to 58 PSI with the pump not running, but it should hold pressure for a long time. If it leaks down right away, you have a leak in the regulator or in the fuel lines. You can also take off the manifold tuning valve at the top of the manifold and look inside, it should all look black. If it looks clean (gold) on the passenger's side, it means the regulator is leaking.Linder Technologies makes a replacement regulator, but you are probably better off replacing the entire injector and the fuel line "nut kit". All of the plastic lines under the manifold get brittle from heat and age.
As long as you have things apart, the EGR valve is in the open and a cleaning of the valve and installation of the TOMCO #2-1357 gasket with a screen is really easy to do. These EGR valves are prone to getting stuck open with carbon and it causes really bad idle and no vacuum for power brakes. I found the gasket at NAPA.
Shop around, and see if you can talk a GM parts counter guy to wholesale you the parts. I think I got out the door for about $415 for all the parts. You can probably do better online.
As I remember, the injector lists at GM for $480 and the nut kit lists for about $80, $15 for the gasket.
I think Autozone has a new aftermarket CPI unit available for $360. There are some rebuilt units available, I think Advance carries them for about $280. I have no idea about the quality.
You'll also need a upper intake gasket. Part numbers are in the links below.
This is not too bad to do yourself on a S-10, Astros look pretty tight under the hood.
Good luck.
Ken G.
See:
http://216.239.57.104/search?q=cache:7GrCX1o2dnIJ:
http://216.239.57.104/search?q=cache:7GrCX1o2dnIJ:
Ken, Thanks for the info and you are right - I didn't give enough information. The van is ab "88 with TBI. From your point of view, how does this change things. I should also mention that the TBI is an aftermarket from NAPA. TIA, Doug
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