Rides smooth as heck but only 8 to 9 mpg
 

Bought 2000 Blazer 4wd with 134,000 miles. Rides smooth but only getting 9 mpg. I put new air filter, cleaned MAF sensor, new generic Autozone ignition coil, new generic Autozone wireset (about $28). generic distr cap and rotor, AC Delco Rapdfre Plat sprk plugs and all three AC Delco oxygen
sensors.

Guy who sold it to me said he had taken distributor out and put it back in
but that maybe I would have to have timing done at a shop. Not sure
what that means.

What do you recommend to improve mileage?

Getting access to a scanner would be nice. To check fuel trims and what the O2 sensors see. You may not be getting closed loop. Thermostat could be stuck open or ECT may not be working. That would keep the engine in open loop ( running rich )
If the distributor was in wrong it would throw a code and run like crap.
Timing is not adjustable. The computer controls the timing based upon readings from the sensors

Your PCM drives temp gauge. What does it say the engine is running at?

What is fuel trims? What is closed loop? Which thermostat could be open?
What is ECT? Sorry but I have no clue what those terms are.

One thing is I have not changed fuel filter. And I dont get any check engine light.

I dont know what PCM drives temp gauge mean. When you say whats the engine running at, are you talking about temp gauge on panel?

Sorry too techincal for me. Thanks anyway.

You'll need to get a hold of a GM factory shop manual, (not Haynes or Chilton) for your vehicle. It will help you with terminology, diagnostic and repair procedures.

Here are a few things that will affect fuel mileage, without turning on the SES light:

First of all, get rid of the Autozone distributor cap and rotor and the AC Delco Rapidfire Platinum spark plugs. Use an AC Delco distributor cap & rotor and AC Delco spark plugs #41-993 with a gap of .060" and put a dab of silicone dielectric grease on each terminal, both inside and out, of the distributor cap.

If the distributor has been out, camshaft retard could be off as much as 25 degrees and NOT set a DTC in memory. This would result in a substantial loss of fuel mileage with no SES light. If camshaft retard is off by 20 degrees, it limits the PCM's ability to control ignition timing by 20 degrees. For that reason alone, it would be a good idea to at least check camshaft retard, (done with a capable scan tool). Adjustment requires rotating the distributor. Spec is zero degrees + or - 2 degrees. If it's off more than ~25 degrees, P1345 will set in memory and turn on the SES light.


With the engine at idle, transmission in park, 2WD selected: Check vacuum at the 4WD actuator under the battery tray. Vacuum should be zero. If vacuum is applied in 2WD, no dash lights will indicate a problem but the front axle will be engaged and fuel mileage will drop significantly.

If fuel pressure is low, or leakdown is excessive, it will affect fuel mileage, and not set a DTC in memory or turn the SES light on. Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off.

He may as well take it to a shop.

I am pretty sure 25 degrees is going to throw a P1345.
He is not going to be able to scan that PID with a generic code reader. If the cam retard is out that much that distributor gear needs to be changed due to wear.

Captain you gave EXCELLENT advice but i believe you may have wasted you're time as he doesnt even know what fuel trims are. No offence to the poster,as alot of people arent mechanic savvy like us.

Poster, take the blazer to a reputable shop and tell them to heck the timing,and to reposition the distributor. They should NOT charge you more then a hours labor.

There are 13 teeth on the distributor gear, each tooth accounts for approximately 27.69 degrees of distributor shaft rotation. If the distributor gear is correctly meshed with the camshaft gear, P1345 will not set. If it's off by one or more teeth, the DTC sets. Which means the threshold is greater than 27.69 degrees. In other words, if camshaft retard if off more than 27.69 degrees, P1345 will set. Elongated wear of the distributor bushings, or a worn gear, will skew camshaft retard readings and affect engine performance without setting P1345.

Thanks Capt Hook, Burned, Chris015. And all others too. Am gonna replace the cap, rotor, spark plugs with the ones suggested here. Maybe the wire set too with
AC Delco 746T. Then I'll take to a shop and have them check the distributor.