Highway power loss

[HyundaiAbuser]

So on a hunting trip yesterday i was driving my 94 mazda B4000 on the highway when suddenty it started slowing down. I floored it but the engine would rev very slowly and slowed to about 1.2k rpm and 40 mph. Then after a minute or so it went back to normal. This happened 4 more times as i drove it home. When i got back i scanned the codes (ford obd1)
181 HEGO (HO2S) sensor fault unable to switch/lean during part throttle
185 Mass airflow sensor below normal
186 Fault in fuel injector pulse width circuit / high
189 which reads the same as 181
114 air charge temperature sensor higher or lower than expected voltage

All of these are new codes along with a 327 EGR valve position circuit below minimum voltage which has been there awhile without problem.
Something interesting extra to note is when filling up i have noticed sometimes gas spills from either the tank or the filler tube.

Any and all help would be appreciated on this im looking to pressure test the fuel system soon if i can.

 

[HyundaiAbuser]

could this be as simple as a fuel filter?

 

[Propflux01]

My thinking as well.The codes being a result.

 

[sloinker]

Unplug the MAF and see if it helps at all. Cheap easy check. Also note if the vehicle runs OK while cold and then gets erratic after it reaches operating temperature. This also indicates a sensor problem. Free checks before you start throwing parts at it.

 

[ctechbob]

Broken up cat can cause similar symptoms as well. Easy enough to check.

 

[HyundaiAbuser]

Originally Posted by ctechbob
Broken up cat can cause similar symptoms as well. Easy enough to check.

how might i check a broken up cat?

 

[HyundaiAbuser]

Also i am certain it is long overdue for a fuel filter so i was planning to do that anyways.

 

[aquariuscsm]

I was thinking MAF sensor as well.

 

[AntsinmyEyes]

Originally Posted by HyundaiAbuser
Originally Posted by ctechbob
Broken up cat can cause similar symptoms as well. Easy enough to check.

how might i check a broken up cat?

 

[Superflan]

Fuel filter, air filter, MAF...

 

[CELICA_XX]

I tried to order a fuel filter for my LS400 at the Lexus dealer while I was diagnosing a similar problem.

The parts manager said... "I don't know what your're trying to fix, but I guarantee you don't need a fuel filter."

He proceeded to tell me that in all the years he worked at the dealer, not one LS400 ever needed a replacement filter.

He was right... It was spark plug wires.

 

[mk378]

The fuel filter will first be noticed as it starves for gas at high rpm and wide open throttle. Back off a little and it should start going OK again.

Likely the IAT and the MAF are inside the same unit here. When the PCM decides a sensor has failed it goes into a compensatory mode to run as best it can without that sensor so you can get home (or to the nearest dealer). This is probably why it picked up and ran better.

 

[pschnahc]

+1 on Check the MAF and associated wiring

 

[HyundaiAbuser]

i just cleaned the maf sensor however due to snowy conditions i havn't driven or really tested it yet. I will drive it to work tomorrow morning and update you guys on the situation.

 

[red7404]

my dad had the habit of saying check the cheapest and easiest things first.

 

[ctechbob]

Originally Posted by HyundaiAbuser
Originally Posted by ctechbob
Broken up cat can cause similar symptoms as well. Easy enough to check.

how might i check a broken up cat?


Sometimes you can get away with smacking the cat with the palm of your hand and listening for lots of little rattles. Will usually sound like chunks rattling around in there. Don't beat it with anything like a hammer or you might cause the very thing you're looking for.

Or if the bolts aren't seized and there's a flange there, you can split it and look into the cat. Little more work though. The SMA pressure test is good as well if you have the means to do it.

 

[clinebarger]

Restricted exhaust concerns aren't normally intermittent unless the substrate has come loose & banged around enough to turn sideways.
Same goes for Fuel Volume/Pressure concerns. As in a clogged filter is clogged. But you could have a temperature related issue with the pump itself.....
*Install a Fuel Pressure Gauge & watch for pressure drop.

DTC's 185 & 186 are related......MAF signal voltage is out of range when compared to TPS signal voltage & Engine RPM. Granted Low Fuel Pressure/Volume and/or Restricted Exhaust can cause the MAF signal voltage to be lower than expected.

Testing EEC-IV MAF signal/output voltages......
*Check the signal/output voltage of the MAF on the Light Blue/Red (LB/R) wire. A typical idle reading will indicate 0.7-1.1 volts. During a quick and hard snap acceleration of the throttle, the voltage of the MAF should react quickly and reach at least 3.0 volts.

*If the reactionary output of the MAF is sluggish and/or does not reach 3.0 volts during the snap acceleration of the throttle, the sensor should be replaced.

*Clear the PCM's adaptive memory during the MAF replacement so that the PCM clears its fuel control strategy back to base. If this is not done the engine may run rich after replacement.



I say replace....Because if this is intermittent....Cleaning it will have ZERO effect

You can also use the above voltage values to Wiggle Test the harness & connector! The Red (R) wire is the Power Feed from the PCM Relay & the Black (B) wire is the Ground.

MAF EEC-IV systems don't really have a good back-up strategy for the MAF, Unplugging it is a fool's errand in my opinion.

 

[HyundaiAbuser]

Ok so after cleaning the MAF sensor and driving my 30 minute trip to work along with the trip back, the only check engine code thrown was the 327 EGR valve position circuit below minimum voltage code which has been there since i bought it. I have also noticed the truck sits about 400 rpm lower to go the same speed on the highway (65). Although its not a confirmed fix since it is intermittent it seems as though this could've solved it.