i recently did a head cam swap and I cant seem to get the car started right. when i turn the key on i can hear the fuel load into the fuel rails. Presure is at 45psi. I crank it and it starts and stumbles at 400 rpm then dies. Next time around i turn it on FP primes itself and the car starts revs to 1200 and dies really fast. 3rd time the car starts right up and idles form 1200-1100-1000 and down like normal then it'll jump from 500 to 900 then give it 3-4 minutes. It'll go into closed loop and the car will idle smoothly at 750. vacume is at 12hg's with the new cam. 112 lsa i sprayed the whole car with carb cleaner and no leaks. i put my thumb on the pvc valve and it almost sucked my finger in lol so I know i'm getting good vacume. timing is at 8* and all the wires, coil and everything is brand new. EVERY sensor is new MAF , knock, mat,CTS, all new maf relays, new egr valve and temp probem. No codes what so ever. Thanks

 

Mkos,

When in open loop, the ECM will use the block learn fuel tables from the PROM until the oxygen sensor becomes active. Since you have made modifications to the engine, these fuel parameters may not be optimum for your engine any more. I'm also presuming that you had the battery disconnected while much of this modification was happening. This means that any learned data was erased, and the ECM was operating on the base tables. Until the intgrator can write the new learned data to the block learn tables, there may be some problems running in open loop. The full compliment of new sensors isn't helping either, since the new sensors probably don't operate in exactly the same ranges as the old ones - they never do. The best solution might be to write a custom PROM if the cam profile is significantly different from the original. (And why else would you change one?)

My guess is that the ECM doesn't like the low vacuum, even though your '89 shouldn't have a MAP sensor. The overlap that is creating the low vacuum is also causing a lean mixture in open loop. Once the O2 is active, the ECM takes full control. Eventually, the ECM integrator may adapt to the new engine parameters, but it will probably not be anywhere close to the desired 128 count baselines in the programming. You may have constant symptoms until you adjust the fuel delivery or write a new PROM.

It is possible that larger injectors at the OEM cold pulse widths would satisfy the ECM, but it would take a scanner to monitor the injector pulses and determine if they are extended beyond the stock programming timings and by how much. That would be a good basis for determining what flow rate would be appropriate.