All Big Six Hhmmm...

Relates to all big sixes

bubba22349

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Congrats you have made a good amount of progress, I think you are real close to finding out what else is needed for your truck to be running really great again! X3 you will need a working O2 unit and it's recommended to replace them at about 75,000 miles, maybe your other parts truck has a good one yet?
 

111JESUS

Active member
Congrats you have made a good amount of progress, I think you are real close to finding out what else is needed for your truck to be running really great again! X3 you will need a working O2 unit and it's recommended to replace them at about 75,000 miles, maybe your other parts truck has a good one yet?
It's pre o2 sensors. I know when I find it I'm going to be kicking myself. One of those things that's like trying to remember the right word for the sentence you are speaking... is it normal for the spout advance to jump the timing 12-14* on an idle soon as you plug the tab back in? Seems like it should maintain close to the 10* mark until throttle up. Yesterday I brushed the power wire harness going into the dist and the engine rpm's went goofy... so I start wiggle test and definite connection issue right where the rubber boot goes under the cap... new place to investigate. Not sure how this thing was running at all with all the issues I'm finding...
 

bubba22349

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It's pre o2 sensors. I know when I find it I'm going to be kicking myself. One of those things that's like trying to remember the right word for the sentence you are speaking... is it normal for the spout advance to jump the timing 12-14* on an idle soon as you plug the tab back in? Seems like it should maintain close to the 10* mark until throttle up. Yesterday I brushed the power wire harness going into the dist and the engine rpm's went goofy... so I start wiggle test and definite connection issue right where the rubber boot goes under the cap... new place to investigate. Not sure how this thing was running at all with all the issues I'm finding...
Yes that is normal for the timing to jump up the 12 to 14 degrees afterwards, once you have set the base setting to 10 degrees at the Idle RPM with the Spout Connector Plug pulled out that is perfect and your done with that part of the tuning. Next after you have repluged in the Spout Connector again the engines ECM takes full control of advancing the timing. Yes it sounds as if your truck had severial issues that should of kept it from running. Hoping those Distribitors wires won't be to much of an issue to repair but when they are that should make another big differance in how it runs too.
 

BigBlue94

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Mine only has an upstream sensor, no downstream.
Speed density only had one O2 sensor. Every ford back to 88 (some as far back as 85) had an O2 sensor. My 96 F350 mentioned above, is speed density. The O2 sensor in the speed density system has NOTHING to do with cats or emissions. Its sole purpose is to make sure the fuel ratio is correct. This is the case with every upstream O2 sensor. If it is not plugged in, you will be stuck in safe mode and you'll be burning more fuel than necessary. If you notice, when I plugged a new sensor back in, I picked up 20% in the mpgs.

The harness for said sensor usually comes over the top of the transmission.
 

111JESUS

Active member
Merry Christmas gentlemen, may the Lord bless you & prosper you.

Well back with further info on the ongoing 95 f150 300 4.9L issue.
Since we last talked I have received a new o2 sensor & rear tank fuel pump from rock auto. Got them installed and altho engine has responded with seemingly a smoother idle and better slow, low throttle increase response. BUT the snap throttle response is still to bog out accompanied at times with some backfires out exhaust. Exhaust has a strong gas smell to it, yet I tried something... during the snap throttle & during the bog response I hit the intake with a snort of brake clean... immediate engine rpm jump up (on the duration of brake clean only). When brk cln burned off bog returned while still holding linkage open by hand...

I then took my probe light w/ voltage read out... and proved inj wires for supply/signal etc. At idle one wire maintain 13.3-5 (this voltage stays consistent during throttle) the other's voltage varies 13.6-8 @ idle to 14.1 - 16.3 on the other wire, varying during snap throttle (same on #1 & #2) no access to other 4 being under the manifold.

I suppose my ? is; what is theory of operation re: ecm to inj... do I have the ecm derating due to no info from egr system (deleted everything & no ecm programming involved) or faulty injectors. I do not have the knowledge of normal voltage signal to injectors from ecm @ differing levels of rpm. During snap throttle the signal voltage changes seem to correspond with the throttle linkage manipulation.
 

sixtseventwo4d

Famous Member
Your ecm needs the feedback information that comes from the egr position sensor. This information directly effects the fuel and timing strategy/adjustments.
The voltage you're seeing at the injectors is correct. The injectors get constant voltage and the ecm only grounds them for a very short time (milliseconds) that you would only see while cranking the engine using your test probe; not while running
 

sixtseventwo4d

Famous Member
If the connector is still there for the egr sensor, it may be possible the get a sensor and connect it but then the ecm would be able to detect it as an inoperative egr which would set a code. It should however let it learn run strategies; provided there are no other missing components that the ecm relies on
 

sdiesel

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and with sensor connected , taping up the probe on the bottom sends a signal to ecu that its functioning. .in theory.
in my harem scarem life arounnd here i have a 351 truck that is exhibiting the same symptoms as yours. my solution? im gonna cut it up. the run rich thing with the o2 malfunction or egr or sooty plugs is a tail chaser. i began the horiffic process of guessing after proper diag. i quit while i was ahead - just. i came to conclusion that if every part was doing its job as noted then the complication must be in communication- the wiring harness. a bone far to big to pick for me and an old v8. nothing accessible, winter on the way. i have to say i cashed out . truck is coming apart. more useful in pieces.
especially considering the remoteness of my destinations and the spontaneous habit of it just dying on me.
is it too much to say that there is an end to li fe of mechanical parts? that they should be just let go of at some point? those eec 4 system was fantastic when new...but it aint no longer and ill grow older trying to nurse it along.
 

Frank

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Supporter 2021
His '95 is MAF, not speed-density, correct? Does that version still depend on the distributor for engine positioning like my '90, or have external position sensors been added? I ask because if the old style, his distributor may be clocked wrong, causing improper injector timing, which may(?) explain the engine operation.
If it is MAF, could the mass air flow sensor cause the lean condition? I've seen a bad MAF sensor cause this on a Chevy.
 

111JESUS

Active member
I believe it is map controlled. The sensor is located up on firewall not down @ air filter area.
Has vacuum line to it off vac tree.

I was thinking of plugging the old egr valve on the harness. I see someone said tape it up as well... what about the vacuum line...? Who am I kidding after the 3 stoogies show this thing has put m ed thru, I'm going to try whatever combination that might work...šŸ¤Ŗ
 

guhfluh

Famous Member
Have you tested MAP voltage readings?
Have you tested TPS voltage readings?
Make sure those voltages are correct and making it TO the PCM.

Your testing indicated excessive lean condition when the brake clean helped. Either the PCM isn't commanding the needed fuel, or the fuel isn't making it through the injectors. If the fuel pressure is correct and not dropping at the rail with throttle, then the injectors could be clogged, but I'd check the electronics first.
 

Frank

Well-known member
Supporter 2021
I believe it is map controlled. The sensor is located up on firewall not down @ air filter area.
Has vacuum line to it off vac tree.

I was thinking of plugging the old egr valve on the harness. I see someone said tape it up as well... what about the vacuum line...? Who am I kidding after the 3 stoogies show this thing has put m ed thru, I'm going to try whatever combination that might work...šŸ¤Ŗ
Ok, that's cleared up. My MAP ran perfectly @ 20 mpg with an aftermarket cam and every emission device removed. Stock ECM. AIR removed, EGR valve physically cut off the manifold, all Evap and Cat removed. Wires were cut and left, all vacuum lines plugged, no artificial signals to any of these removed sensors. If yours is MAP, the EGR signal is not causing this problem.
Verify the vacuum signal to the MAP sensor. You can test it by pulling the vacuum line off with engine running, engine should immediately go flooding-rich. If it doesn't, this is your cause of the lean open throttle problem. Be sure the distributor is clocked. The Hall Effect trigger is different for #1, and that is what tells the injectors when to fire. Be sure cap is mounted correctly, and #1 marked on the cap is going to #1 cylinder.
Best wishes. I still am of the firm opinion that you have either a fuel supply (pressure) problem, incorrect distributor orientation or a faulty MAP sensor. EGR and other emission controls affect timing and mixture, but NOT to the point of your stalling-lean condition.
 
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