Ok, just got the MAF sensor in and installed it. It does read better then the old one, around 3.2g/sec vs 5.2 at idle and it seems to help a little it was not the issue. It stil has zero power and refuses to rev above 4k.
A clogged cat is a possible issue I suppose given the issues but the exhaust is all rusted and not sure I can even check it without breaking every bolt and without a welder I have no way to put things back together if that happens.
Guess I will start soaking the bolts in penetrating oil and give it a try at some point as I can’t think of anything else to try beside throwing parts at it and it is not worth that.
I am open to anything at this point, much more and I will be forced to give up on it and put my time and money into getting the 4runner back on the road.
How can you adjust the tune on the ford? If I could do that I should be able to track down the issue via trial and error.
I am spoiled by standalone / piggyback ECU’s where I would simply datalog and adjust the tune to figure out the issue fairly easily.
I was getting a strange issue earlier where when free revving it at around 30% throttle it would hit 3k RPM and then start stumbling and basically refuse to rev past it for 30-90 seconds until it finally got above 3k, then it would do it’s thing up to 4k.
It was repeatable and very odd, if I went WOT it would not do it, only at part throttle.
While stumbling I watched all the sensors I could and could not find anything unexpected, really annoying.
Unno, a lot of it still sounds like an ignition problem, the dreaded “weak spark”. Might idle fine, get to some low-stress rpms, but under any load the mix just “blows out the spark”.
My old Cav had a plugged cat. Loss of power that just got progressively worse ’til it could only go a quarter-mile or so ’til it stalled. Like a banana up the tailpipe. Letting it sit a while, it’d “deflate” and let me go another quarter-mile, maybe more if I was able to just putz along with a barely-cracked throttle. Fun fun fun on the 495…
Still loved that car. Ran lean’n’clean, and for years before that with a hollow cat, and still passed smog ’til NYS literally halved max emissions one year.
But yeah, that cat rang like a bell if you’d hit it. Much much much better when hollow, than when the working replacement got plugged.
Yeah, spark issue is still a possibility, I have not had time to go get new plugs but honestly I don’t have a lot of hope in that, the issue just started too suddenly for me to see that being the issue but anything is possible at this point.
I would gladly just gut the cat if I could get in there. On my 4runner I built a box that tricks the ECU into thinking the cat is still in place, it is fairly simple, just a few resistors and a diode to reduce the readings on the 2nd cat and thus make it looks like the cat is working. I would think it would work on the ford as well, just might have to play with the resistance some.
A plugged cat would happen rather slowly, but a blocked muffler, if the baffles break off and block the hole, can happen suddenly, but you’d probably notice a change in the exhaust note.
Insulation in the coil or a coil wire could break/split and let the spark “leak” outside vs at the plug, or a loose connection could increase the resistance and limit the voltage, anything. Would be at something in common to all, vs just one plug or plug-wire.
Nowadays OBD sniffs both before and after the cat, and if the readings track too closely, it throws an error (supposta be a bit of lag, not instantly tracking).
Yeah, that is how my 4runner works as well. I forgot the exact layout of the box I put together but it had some resistors, a diode or 2 and possibly a cap/inductor. I built it over 10 years ago and have not touched it since lol.
It worked though, never threw a code and passes inspection every year.
People gave me a hard time back when I built it as well saying it would not work, 10+ years later it is still working lol.
Watching the O2 signals it delayed the response and reduced the readings slightly.
The real issue on the ford would be the temp sensor would have to be tricked as well or it would not read high enough.
Yeh, before the cat bounces up’n’down fairly quickly as the fuel-trim is adjusted, but after the cat has all kinds of lag which “smooths” the output. RC network would work well.
Well that’s a significant difference in readings, but a plugged exhaust that’s getting worse would also reduce your readings. Did you recheck the old MAF readings the same day as the new one?
Two diagnostics is recommend are 1: a vacuum gauge test and 2: watching the run engine in the dark.
The vacuum test should help point out the potential exhaust back pressure issue. If you could rent a back pressure gauge and tap into the o2 sensor that would be ideal…
The reason for viewing the engine in the dark is for watching for ignition system shorts. I’ve caught bad plug wires arcing this way before. Free and easy…
About the engine in the dark, yeah check both when cold and when good and hot.
Had a 1970 Ford panel van with 6cyl. and it got down on power where you had to slam it into 2nd gear (3 on the Tree) to make medium steep grade hills.
Pulled the dog house one night and all the wires were glowing and arcing.
Next day replaced wires and ran like new engine, had to lower idle down even. Taught me to test for that on all cars since. Also have had a bad ignition wire when new, it does happen, so when people say well the wires are new OK but are they performing correctly.
Don’t think that is the problem here as his truck seems to go bad like someone is throwing a switch.
Where I live there are cheap Pull Your Own junkyards and I would be tempted to just go get the main computer if it is cheap enough and see what gives.
Had one take a crap on a Jeep, had lots of random electrical gremlins, replaced it and wala:)
Sadly with a coil on plug setup you would not be able to see any of the high voltage ignition areas so that test would not help much I am afraid.
Indeed, it will run normally sometimes and then run bad again a second later like throwing a switch, which is why I am basically positive it is an electronics issue but nothing shows up on the OBD scanner.
The ECU is something I have considered a few times but the cheapest I have found one is $50+, that is a lot to waste on a longshot like that, particularly on a car only worth maybe $500 in it’s current condition.
Vacuum seems normal according to the OBD, it reads in absolute but gets down around ~3-4psi at idle which sounds about right.
I would recommend checking the vacuum with a manual/analog gauge, as the refresh rate often hides the more subtle behaviors.
I was going to suggest the same thing as Muto with going to a U-Pull-It for some random sensors etc…
Crank and cam pos sensors primarily.
BTW, does your OBD readout have a knock count? This is an issue that should surely trigger a DTC, but I am curious if it somehow its detecting knock and pulling timing/richening A:F
It did have a knock readout of some kind but it never triggered even when I could hear it pinging. I tested the knock sensor when the intake was off and it seems to be good, so this is another reason I suspect something deeper then a basic sensor error. That or the knock detection sucks on these ECU’s.
In my 4runner the knock detection is really good, you can get away with an amazing amount of abuse because of it lol.
I might toss a mechanical vacuum gauge on it and see what it reads, although so far everything has checked out as matching the OBD readout so loosing hope.
Going to try putting in my old spark plugs / coils today (have not been able to bum a ride to the parts store) to see if it shows any improvements, the plugs worked fine when I replaced them.
After this, sadly going to have to put it out to pasture for the time being so I can work on the 4runner, I am out of ideas for the Ford outside of the ECU itself.
Well, just swapped to the old coils and plugs, no change. I would of expected some kind of change if they were the issue.
The really strange part is that once again, it runs perfectly for the first few seconds after a cold start when still in open loop. Then it goes into closed loop and the issues start.
Pretty much rules out any mechanical, fuel, clogged exhaust or timing issue as those would effect open loop as well.
Just replaced the MAF. I could not find my vacuum gauge but the readings seem on point for the MAP sensor or at least close enough to not cause this big of an issue.
Anyone else have any bright ideas?
Only thing I can figure at this point would be the ECU itself but that is a lot to spend on a long shot. I have replaced the ECU in a few cars in the past with strange issues and it never worked before.
Hard to say exactly as I have not timed it, ~15 seconds or so I would guess today from a cold start. When it is already hot it is shorter.
I was watching the OBD at one point when it left open loop and the instant it did is when the issues started.
I have noticed this since I got it, just not as pronounced. When I would first start it up in the morning it would be really peppy and drive great until I was at the end of the block, by the time I took off from there it would be back to it’s old down on power ways.
Okay. Well let’s try and force it to stay in open loop for an experiment. Try disconnecting coolant temp sensor and see if that keeps it OL. If not, then disconnecting the upstream O2 sensor should. These will obviously cause a CEL but this can really point us in the right direction
EDIT: if it only took about 15 seconds from cold, then it’s likely the heated o2 sensor determining the switchover point. Coolant temp may not help
Interesting idea, I was wondering how I would go about forcing it into open loop but I worked with standalones or tuneable ECU’s for so long I never really learned what would cause a stock ECU to do that.
I will try the temp sensor first, assuming I can get at it. I remember disconnecting a plug next to the tstat when doing the intake manifold and not sure I can get to that plug with the manifold in place.
