Engine mystery..please help (long description!)
 

Hey all. This problem may be difficult to explain but I will try my best.

Engine: D16Z6 in a 91 Si

OK. The engine idles fine (seems to dip down to 500rmp every once in a while but it has always done that) and it runs great above 3000rpm or the whole bandwidth when the car is cold (ie. morning driving).

Problem: when I am stopped and I try to accelerate the engine stops, it does NOT stall but just does not accelerate. I can hold the gas pedal down and the RPMs will try to go up but the needle just sort of bobs around 2krpm and grunts at me. If I launch carefully from about 3000rpm and am very careful when I release the clutch then I can launch.When shifting gears, if I go into 2nd in the low rpm range and try to press the gas, then again the engine just doesnt do anything.

It seems that I need to let off the gas and let it get back to idle speed and then SLOWLY press the gas(like barely pressing it until its gets up to 2500-3000) to get it to accelerate. Again, the car does not stall, i just need to let off the gas and go really slow.

I have 'floored' the peddle when this happens and the rev's just hang around 1500-2000 and the engine sputters for about 3-5 secs and then finally it catches and it shoots up to 6krpm.

The spark plugs indicate the engine is running lean (but it always has a little). I have replaced the plugs, wires and had the dizzy looked at and it is all good. I replaced my fuel filter and cleaned the injectors. I seem to burn through plugs in about 2 months. Im also not throwing any engine codes

It seems to me that there is no low end power because when Im cruising, and driving when the engine is colder, it runs fantastic. IT is just when I need torque that it does this. Being stopped on a slight hill (uphill) really makes this problem more prominant (again, I guess because no torque is required)

I had my Catalytic converter and full exhaust changed a few(maybe 8) months ago. I had a "hi-flow- cat installed. Now, I dont know too much about this stuff but my guess is that when the cat is warm maybe the exhaust gas is not getting through at low rpms so Im getting exhaust gas back into the engine and this may be causing this to happen?? Does this make sense? This makes the most sense to me but I could be way off. Or could it just be a fuel problem? I initially thought this but like I said the car runs great when cruising, idling and when cold.

Im apologize for the long description but it is a difficult thing to try and explain without seeing what Im talking about.

I would appreciate any help anyone could provide. I was thinking of hitting my muffler shop tomorrow but I wanted to advise first.

Thanks in advance

answer these questions first

how does it idle when cold? (first starting)

has it always been like this? or just recently started acting up

what ecu? conversion harness? converted any clips?

to me, o2 sensor popped into my head right away, but as I read on it doesnt really seem liek it.

when cold it idles really high, like 2k and then drops after about 1 min to 800 or so. It always been like this, although it has gradually gone higher over the years.

I have the stock 91 ecu with a swith mounted near the throttle cable activating vtec.

I had a new SRI(vibrant) installed about 1 year ago(not by me) and it does have a tube running from the crankcase to the intake pipe, this was not present on my old intake(which was just the stock piping with a K&N filter on the end). Could this be adding to the problem? if so, where do I do with that tube?

so you are using a non-vtec ecu with a vtec engine?
Ditch that switch setup and get a vtec ecu....NOW. When using a vtec ecu when vtec engages the ecu will switch over to the vtec fuel/ignition map (which have different fuel/ignition values than the non-vtec maps). But when NOT using a vtec ecu and just having a switch activate vtec, the ecu WILL NOT switch over to the vtec maps (b/c the ecu doesn't have any vtec maps to switch over to) and continue to run off the non-vtec fuel/ignition maps, which is an extremely ghetto way of doing it.
Now you have a few options, you can stay obd0, grab a PW0 or PR3 (dohc vtec) ecu and chip it with the d16z6 maps (which it'll probably be pretty hard to find an obd0 d16z6 program), or get an obd1 distributor, obd1 ecu (you can even use a stock p28, but a chipped p28 is a good idea) and obd0 to obd1 ecu conversion harness and run a p28. I'm willing to bet this will greatly improve the cars driveability (provided there isn't something mechanical wrong with your car) b/c you'll be using the proper fuel/ignition maps for that engine, not to mention be a hell of a lot safer than running a d16a6 ecu (the fuel maps are way different between the d16z6 and d16a6). I'm guessing the car runs ok when its cold b/c when the ECT (engine coolant temps) are low the ecu jacks the fuel up (b/c we don't have a choke on our engines to decrease the airflow that gets to the engine) to keep the engine safe, and while cruising/idling it runs ok b/c the engine requires such little fuel and will run "decent" under a wide array of air/fuel ratios.
But the first thing i would do is get the right ecu and wire up vtec properly....going through spark plugs so quick is the first sign that the fuel delivery isn't sufficient and that you need to do something about that.

thanks for the info. Unfortunalty I really do not have the time for this and frankly im getting rid of the car near the end of the year so I dont want to invest any cash in it.

I have had this swap setup for years(swap was done in 2002). Vtec was setup with a switch near the throttle cable (which I know broke due to my excessive flooring of the gas peddle.)

How much to get all the parts and have someone do this? the only time I have is on weekends and most shops arent open then. Can this be done in the driveway? do you know anyone that could help do it?

as andrew said.. get the proper ecu first, so that your car is running right. Guaranteed that will help a bit in the driveabitily.

Since you said you have a normal cold start-up, i would assume it may be a bad o2 causing your hesistation. Hook up a labscope to it. Or I dont know if zeeman can get the o2 readings on his loggger? Wait for him to chime in.

As for getting the right ecu and basemap, zeeman is the guy.. he does all the tuning, ecu chipping, conversion harnesses around here.

please PM me for any info about chipping/harness/work you may need.