So literally overnight my 97 Blazer 4x4 went from 22mpg hwy to roughly 11. It bogs very noticeably under light to moderate acceleration. It's been ongoing about a week now. Before this occurred I have rebuilt the spider injector (o-ring replacement), replaced spark plugs, ign. wires, dizzy cap and rotor, air filter, fuel filter, and the fuel pump. I am also running 2WD rims with 29" tires, but had been running the setup for about a week before the issue.

I have done a fuel pressure leak down test and driving test, here are the results.

Key on: 60 PSI
Key off for 10 minutes: 60 PSI
Key off for 4 hours: 20 PSI (possible gauge leak issue)
Engine on at idle: 55 PSI
Under moderate acceleration: 60 PSI
Heavy acceleration to WOT: 65 PSI
Back to cruising: 55 PSI

I also have live data values at idle with the engine warmed up to 199F in closed loop. The RPM jumps between 570-700 and the spark advance seems a little high at 18-21 degrees, but not really sure if that's normal range.

-Mass Air Flow: 0.64lb/min
-Short term fuel Bank 1: -2.34%
-Long term fuel Bank 1: 9.38%
-Short Term Bank 2: -0.78%
-Long Term Bank 2: 5.47%
-MAP: 12.11hg (Isn't this low?)
-02 B1S1: 0.82v STFT -0.78%
-02 B1S2: 0.1v STFT 99.22% (WTH?)
-02 B1S3: 0.28v STFT 99.22%
-02 B2S1: 0.8v -1.56%

I will try to get some Min and Max variables on my way to work tomorrow. Any help is appreciated.

 

• 30.00 barometric pressure - 12.11 MAP pressure = 17.89 vacuum
• Long term FT is positive - this means extra fuel is being added to the factory calibration - engine is trying to run lean and is being corrected. Generally ±10 is considered OK. Your bank one is on the edge.
• Short term fuel trim and O2 sensor voltages are worthless unless you plot them so you can watch them cycle.
• Spark advance data is worthless in this case.
• Fuel pump pressures seem normal for the things that you tested, as long as you have the upgrade MPFI injectors. If not, then your fuel pressure is too low.

Plot short term fuel trim (not display current digital value). If worse (away from 0) at idle, then you may have a vacuum leak or a fuel problem of some sort.

Find a OBD2 scanner that will display cam sensor retard (rotor position). This should be 0 ± 2.0°. If not then you have danger of misfiring inside the distributor.

My 4x4 blazer gets 14 - 21 mpg. 21 only on straight level road at 55 mph with A/C off.

Good luck and best wishes for a successful repair

 

I can't believe I didn't even notice that number! It was 2am however and the 99% through me for a little loop.. and this has gotten me frustrated.

I've actually been meaning to replace my vacuum lines being I found them rotten and unhooked in the engine bay. However, the brake check valve is capped off. Which is another thing, aren't these 97's still vacuum actuated for the 4WD? Because mine locks in and out fine.. odd.

I'm running a stock spider assembly. My Haynes manual said the key on pressure and idle pressure should be fine, but is that so or how should they differ? I have no idea what the driving/load pressure should be. Can't seem to find it anywhere.

I'm working with my new OBDII software for the laptop, TouchScan. I'm in the trial run because I want to try a few different ones before I make a purchase, hopefully beats buying another Solus for 4K, which was nice with the programmable options and solenoid/valve operations, but had to sell her when I was down on work. But that was one thing I did notice last night, was that there wasn't an option for the CSR nor MAP and MAF voltage readings. If you know of some decent software let me know man.

However, I will get some log data running on the way back to the house from work and review it once I get home and post some feed back. I'd rather do this correctly rather than sling parts I don't need. Thanks!

 

So I have snapshots of recording at an idle for STFT and LTFT Bank 1 and 2. They begin at the 30 sec. mark and span over a minute period. Stayed steady at 6.3 on LTFT Bank 1 for quite some time, which isn't too bad I presume.

I also have a recording of highway driving at 75mph for 15 minutes, the rest city. I take this way to work everyday, and the road has a decent amount of hills. I'm still trying to squeeze it down if you think it would make a difference with you helping me review it as well.

 

Well something on Bank 1 is making the LTFT higher than the fuel trim at idle. Idle STFT is very close to zero so I think that rules out vacuum leaks and EGR sticking.

So what is STFT of bank 1 doing at 75MPH in the clip you already took.

I would be interested in looking at a Bank 1 STFT clip of steady idle, and then holding steady speed around 2500 rpm in 3rd. Maybe 30 sec each. Do the same for Bank 2.

Also look at the individual misfire counters - they count up quite fast if you have a misfire that would affect fuel efficiency.

 

I know of two fairly inexpensive softwares that will do a good job on a 97 Blazer (96/97 is different from 98+). They are both from the same company (Palmer) and both do cam sensor retard. Neither does crank sensor relearn.

First one is Dash Command for Android (or iPhone I hear). Uses Bluetooth OBD2 adapter. $10 base + $10 each vehicle for extended PIDs. Use BAFX OBD2 adapter from Amazon ($22) - so total is about $42

Second one is Scan XL Pro for Windows. Will use same wireless OBD2 or inexpensive hardwire USB from Scantool.net. ~$150 and does not require extra for each vehicle extended PIDs. With the cheap hardwire USB OBD2 this is lightning fast in reading PID data.

If you want to do crank sensor relearns and have bidirectional control, you need software such as EFI Live, HP Tuners, and Autoenginuity. These are all windows based, start at about $350, and include the OBD2 interface. I think oen of the mods Swartkk (sp?) has an Autoenginuity for sale. I have HP tuners, but have heard especially good things about Autoenginuity.

 

I will get those posted up for you tonight man. Laptop's with me, but no wifi at work lol. I did another recording today that's not as long I can easily trim down.

Just to make sure, may be a dumb question, but you want me to ride third gear at 2500 rpm or just rev at idle for the 3rd clip? Reason for asking is I have an automatic, lol.

STFT on Bank 1 looks relatively the same. It doesn't cross zero as much, but it doesn't go to far past -3.9 or +3.9.

I was actually looking into Scan XL. I've seen a lot of good reviews on it and I think I'll give it a shot. As far as Autoenginuity and HP tuners, I'll take your word and do some research into it. I have a plan to build an engine for this next year, and I'd like something with a little more performance monitoring and adjustment options for sure. And I'd for sure rather run a windows program. USB connection always seems to read quicker than Bluetooth.

 

One other thing. Since the STFT at idle is staying close to zero for Bank 1, and that rules out a vacuum issue, would it also rule out compression? I was originally worried my issue may be from a blown head gasket. Vehicle runs warm when sitting still. Probably clutch fan, but I'm going to be replacing the entire cooling system due to antifreeze being against the previous owner's religion.

I will do a compression and leak down check on bank 1 just to be safe. But, with a shot head gasket, wouldn't it be trying to run so lean that STFT would be heavily compensating? I could be wrong, but I would imagine this is the case.

 

yeah, how about STFT at 2500 in 3rd going steady down the highway (keep from going into OD to keep the rpms up a bit). That should be under 70 mph.

 

I believe a misfire of any kind would leave extra oxygen in the exhaust and this would be interpreted as being lean - so STFT would go positive as it tries to richen the mix to compensate. Make sense?

What about reading live misfire counters when going down the highway steady? Any luck with that using your current scanner?