Have a question that I am trying to figure out. I am resurrecting an 86 l98 4+3 and it is going better than I ever expected - but....
When first started the engine idles fine but completely boggs with any throttle input. When it is completely warmed up it runs much better. It has tons of power and it is great to be back in a Vette (used to have a 79 L98). It seems to take an eternity to warm up also but that is another story. Regarding the components in the engine - I have no idea. From my detective work it appears that the engine was worked on. All the bellhousing bolts were loose (sounds like rods knocking if anybody wants to know) and both motor mount bolts were almost completely undone. Inside the engine is very clean from what I can tell (had the oil pan off yesterday). Also it is an early 86 but I have the aluminum heads ??? VIN is #103666

So far the fuel pump has been replaced and using the pressure gauge it reads 45psi when I turn the key on (it holds that for several hours) and is at 37-39 when idling. I checked the TPS and it reads .54 at idle and 4.7 at WOT (I did not check the smoothness of the readings though). I did a compression check and they are all between 140 and 150. I changed the throttle body gaskets and cleaned it. I checked the IAC and cleaned it but did not check the measurement of the pintle.The idling on the car is a little off at times but mostly it is good. I have the cold start disconnected (electrically) - it seems to make no difference. EGR is there but not working (wont hold vacuum) but spraying carb cleaner does not make a difference in idle - also sprayed down everything else and replaced all the vacuum lines. Replaced the MAF and both relays (was getting that code when I finally got it started). Removed all the AIR system components.

Could it be the injectors? Contacted Jon from FIC and getting ready to order a set anyway. They ohmed out fine - all about 16.5 - hot and cold.

Just put long tube headers on it with a heated O2 sensor that are currently all there is (damn its loud) - so no restricted exhaust.

She has come a long way from the sight unseen 77,000 mile "project" that I purchased for 1500. All of the usual "non working" components actually work (after chasing down the wiring problems) - anybody ever seen the main harness that goes under the brake booster get caught in the steering column? What a mess. The body is straight (hood needs adjusting - PITA) but the third paint job is garbage (all complete color changes too - gold to red to black). The interior is gutted now - but she is coming along nicely. The original seats are faded but no cracks or rips - unbelievable.

Anyway, sorry for the long post and you folks have been an unbelievable resource to my project. This forum is incredible. Thank you all but I could not seem to find this problem by searching so here it goes....

 

What's an eternity in real seconds/minutes....

Closed loop/ open loop

 

I haven't actually timed it but it hits 180 at about 5-7 minutes and things get better (I can actually hear the idle change) and then when it hits 200-220 it is running very good. I thought that maybe the thermostat was removed but feeling the upper hose - it is soft until about 160 or so - I need to change that also. I put a reman ECM and the stock chip in it.

 

One more the thing - I have looked all through the FSM and I have yet to find an exact way to determine if I am in Closed or Open loop.
Also I am not currently getting any error codes - just 12. It was a happy day when I could drive around the neighborhood (no license plate or insurance yet) and not have the Check Engine light come on.

 

I belive code 12 is a test code that lets you know the system is working properly and no codes are save or stored in the computer. my 88' idles wierd when i first fire it up and is in closed loop, it still idles funky for about 30 seconds when it goes into open loop... i know i have a leaky injector that might be my cause

 

Be happy, mine runs great when i start it, then about 20 secs later it idles like a dragster, which would be fine if it were a dragster.

 

With all those loose bolts, I'd really check the ecm ground bolts on the back of the head(s).

 

Doesn't sound like injectors to me. I would continue to look elsewhere. I would also see if you have a thermostat and if it's working. Some people put 160* stats in a L98 which is dumb. Stock is 195* and 180* is as low as I would go. Also, if you disconnect the battery the ECM will need some re learning time so drive it a while after you disconnect.

 

Since you hear the idle change AND since the injector ohm out correctly, I'm inclinded to agree that injector funtion is not a problem. OTOH, if this has been modified, you probably don't know the injector size and/or if a (computer) tune has been installed.

Sounds like you don't know (or aren't sure of) the history of this motor. The first thing I'd do is get TunerPro and an ALDL cable to learn what this motor is doing. Because it improves upon warm-up and you hear the idle change, I'd bet you're hitting closed loop. From a cold start, it occurs after 5 minutes. That's when O2 sensor feedback starts sending feedback to the ECM -- which can adjust for a (somewhat) poor fuel mixture.

Another possibility is the prior owner didn't know how to -- or did not do any kind of a computer change. It could need a tune or be flat out wrong. For the peace of mine, I wouldn't own an ODB1 engine w/o knowing the history and/or scanning what's going on.

 

IIRC there is an lt1 intake on it...if the oem 22 lb injectors are still in use and stock ecm chip calling signals, the added air flow with the lt1 intake vs tpi will result in 'lean bog' until the ecm goes 'closed loop' and learns/adds more fuel...24.7 lb oem lt1 injectors are the 'ez' cure for this.

 

Hey everybody,
Just to clear a few things up - this was from a year ago when I first got it to start and run.
Fast forward to now - 385, WC T5, modded LT1 intake, 30 lb injectors and custom tuning by mseven.

The only thing still the same is the block and oil pan.

But thanks for caring and for using the "search" function.