The car is a 1986 Monte Carlo SS, L69 (305ho) with a 86 - 88 tune port fuel injection from an F-body. It is the 9th injector MAS system wired with a painless wiring harness. All relays, sensors, ESC modules are new GM units. I am using an F-body TPI fuel filter that is mounted just after the tank above the heatsheild where the fuel lines go into the frame. The fuel pump is a Walbro 255LPH intank pump. The injectors are factory GM 350 cu in injectors. I think 21 lb per hour. I have the GM coil-in-cap distributor. I have longtube Flowtech non-emission headers with a 4 wire GM heated O2 sensor mounted in the collector of the left (driverside) header. The EGR is the only emissions that is functioning. The engine is original with 107,500 miles. The TPI conversion has been operational since 105,100 miles

Sysmpton:
At idle (about 650 in gear) the car will stumble and then the SES light comes on. As soon as I take off and get up to speed, the light goes out.

Scanner Info:
Plugged in to a scanner to see what was going on. Scanner shows that in closed loop mode, at and idle of 650 to 700 rpms, the O2 sensor is showing only 4 to 8 milli-volts indicating a lean mixture. When the SES light comes on, the computer defaults back to open loop mode until I accelerate, then it returns back to close loop mode. On the road at any speed, the O2 sensor indicates 510 to 650 milli-volts(depending on how far the accelerator is pressed) indicating that everything is normal.

Fuel pressure: at idle is 40 to 41 psi
at WOT is 45 to 46 psi
TPS is .54 volts at fully closed throttle

Operating Temperature is 190 to 220. The fans come on at 220 and go off at 180.

Out side temperature is 95 to 100 degrees during mid-day.

When I changed the plugs, I noticed that all the plugs looked pretty good with light tan almost gray deposits on the electrode except no 7 plug. It was blistered! The plugs that were in when this situation began were Bosch platinum BP9. These were the plugs that were in the car before the TPI swap. I am now running Autolite 24's.

The car seems to run very strong. No other codes are stored.

What should I do to remedy this?

 

Bad o2?

HEader leaks near or pre 02?

Vacuum leaks that would make it think its lean?

Check the basics and work from there?

Does it have headers or manifolds?

later
Jeremy

 

Flowtech longtube non-emissions headers. I just replaced the header gaskets this weekend, just to be sure that was not the problem.

 

Could be one or more plugged injectors causing the lean condition. If the engine has a knock sensor the stumble at idle is probably causing the SES light.

 

todd, we met at the cruise at DQ a couple months ago and i THINK i remember you saying that the ECM you had was out of a manual car and your car is an auto. i've read something on here about issues arising from using an ECM meant for a car with a different tranny could cause stumbling because the ECM has to have some signal from the VSS. i'm nowhere near being an expert on this, would anybody care to elaborate on the subject? once i fix all of the stuff i broke last week i'll need to know this info too because my ecm came from an auto car.

 

I swapped chips in the ECM for a 5.0 TPI with automatic. My other chip is for a manual tranny without the ninth coldstart injector. It would not even start on that chip, because in 1989, GM did the coldstart enrichment through the existing 8 injectors and did away with the 9th injector.

 

Check your intake manifold bolts (the ones you can get to) for tightness (45#). If you find any loose it may pay to do whatever disassembly necessary to get to the hidden ones.

 

Headers?

Try running an AFS 74 heated Delco sensor.

could just be the 02 running too cold and not transitioning and cross counting.

later
Jeremy

 

I suspect that the reason it would not start was not because of the CSI, but because of VATS enable in the 1989 PROM.

 

I had the same problem yesterday, found a vacume leak at the cold start injector... slobbered it up with some rtv seal and jacked up the fuel pressure to about 48 psi, no more code 44.

 

if injectors leak or whatever like 0-rings failing. woudlnt there be fuel leaking onto the valve covers or intake manifold or spitttign whereever it pleases?