Typical idle sensor readings.
 

Hey guys,

I'm trying to track down a rich engine condition. I datalogged 5 minutes of idle once the motor warmed up. My results are below:

This is on an '87 L98

MAF: 8-9.5 g/s
BLM: 108 most of the time
INT: 90-125
Fuel Trim: 0 - 1
TPS: 0.51V
IAC: 40-90 counts
Injector PW: 0.7-2
Injector DC: 1-2.4%
O2: 800-850mV the whole time
Spark Advance: 25-26 degrees
CTS: 177-183 degrees
IAT: 136-138 degrees

These results look pretty normal to me except for O2 voltage and BLMs. Agreed?

The motor is spitting out rich black exhaust. I've tested the injectors and they are not leaking, including the cold start injector. I've run a series of test and determined that the fuel pump isn't holding pressure. The fuel rail and pressure regulator will hold pressure if the fuel supply line is pinched. I am only getting 25 PSI at the rail while idling. But I'm not sure how this could give me a rich condition.

The computer seems to recognize the engine is rich, but is doing nothing about it.

Thanks,
John

Re: Typical idle sensor readings.
 

BLM- low
TPS- little low
IAC- I like lower nbrs but for a stocker its ok
O2- high should bounce between 200-800mV (approx)

The ECM sees its rich and tries to compensat (BLM) but cant compensate enough (BLM = 108)

Done any changes lately?

Fix the Fuel pressure problem, then see how its doing. Depending on results maybe a newO2 is the next step.

/N.

Re: Typical idle sensor readings.
 

First I should mention the details on the motor.

350TPI
24lb injectors - injector constant adjusted in prom
Trickflow 195's
Headers/exhaust
Edelbrock intake manifold, AS&M runners
ZZ4 cam

I'm not to worried about the IAC counts because I'm sure the wild rich condition is causing idle problems.

I'm actually not with the car right now. I will be next week. So I'm trying to formulate a game plan. I know I need a new fuel pump, but would this cause a rich condition?

This is the latest in a line of problems I've had with the car. 4 weeks ago I replaced the water pump because of noisy bearings. After this install, the car immediately starting running really poorly. It was bucking/stumbling to the point of being undriveable. The bucking would occur at any throttle input. It would idle ok. The car has a Moates G1 adapter with the stock memcal attached to maintain 'limp home' functionality. While trying to diagnose the stumbling/bucking I noticed that I could not datalog, I could not get a connection with the ECM. When I removed the stock memcal from the G1 adapter, the bucking and stumbling went away, and I was able to data log from the ECM. Therefore the car was running fine on the aftermarket PROM but poorly with the stock memcal attached. I also tried running the car on just the stock memcal with no G1 adapter and I got the same bucking/stumbling. So I concluded the stock memcal somehow broke and was forcing the motor into 'limp home' mode. Right now I am running the car with just the G1 adapter + aftermarket prom.

So the motor ran much better without the stock memcal but is running extremely rich. Now I'm diagnosing that problem. Seems strange that the stock memcal would break during a water pump install, I did removing the negative battery cable during the install. It also seems strange the fuel pump would break at the same time. I can't help but think these issues are related.

Thanks for the help.

Re: Typical idle sensor readings.
 

I am interested in this answer because when I am using the EBL my BLM sits at 108 at about 55 MPH and 1800 RPM. This started when I changed to larger injectors (55# to 68#). I did crank the FP down from 16 to 12 (55# @ 16 = 61, 68# @ 12 = 65). I changed the plugs and O2, but I think I need to crank the FP down some more because it is going into asynch mode at idle. I think the 55# injectors were not actually putting out 55# - I was going static at WOT. It is confusing to me, however, why the BLM sits at 108 at cruise. The LO5 I have was supposed to have 61# injectors and I have some mods so I would not think setting the 68# injectors to put out 65# would cause a problem. I am on the road and will not have an opportunity to back down the pressure until this weekend.