Calling all you Diagnostic Gurus | SOLVED Stumbling on hard acceleration THANKS EVERYONE

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White Stripe said:
I understand that, but it also tells the ecu where the timing is.
Click to expand...
Sort of.
There is no feedback to the distributor from the ECU. The distributor is simply supplying 2 sets of tach pulses to the ECU which it processes according to its programming. Timing will depend on throttle position, knock sensors (if so equipped), AFM input, etc., but it is all done by the ECU.
Again, the distributor does not change or alter timing in any way.

On the 3FE, the crank position sensor was one of the tach pulses in the distributor. On the 1FZ-FE (I think both US spec versions) there is a separate crank position sensor that the ECU uses to reference timing.

Check that, the ECU uses the camshaft position sensor (one of the tack pulses) in the distributor to reference timing on the 1FZ, just like the 3FE. The crank sensor monitors RPM according to the FSM.
 
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awesome said:
Check your knock sensors , there are two of them.
Click to expand...

The thought had crossed my mind, but there has never been a code indicating an issue with that circuit. I feel a knock sensor would certainly trigger a code.
 
Update:

Tonight I did the most important work towards finding the issue....I detailed the old girl, got down and dirty with the carpet, rubbed her belly and patted her on the head. Shockingly this had no effect on the issue. I know I'm as confounded as you all!

But seriously the plan is to do some part swaps with my buddy's cruiser this Saturday which should give us some good intel. I spent the rest of the evening rigging up and aiming the parts cannon at the engine bay just in case.
 
Midday update:
  • Swapped over distributor - NO CHANGE
  • Swapped over Ignitor - NO CHANGE
So to date, I've done the following:
  1. Cleaned all grounds and + terminals
  2. Swapped ECU with my Spare
  3. Swapped Wires, Distributor Cap, Rotor with my Spares
  4. Swapped Coil with my spare
  5. Checked the AFM per the FSM and it passed every test (see post for info)
  6. Set timing back to 5 degrees
  7. Tested Fuel Pump Voltage at the pump, noted it was low on high flow, hot-wired to get 13+ volts to it at high flow. NO CHANGE
  8. Check Engine Codes have not returned since the original post
With everything above checking out I think it's safe to say the issue isn't in the ignition side. Here's some more info that we noted while testing it today:

The stumble happens under 3/4 to full throttle (load) more noticeably / harsher at 2500 - 3000 then less harsh but still noticeable at 3000-4000, and not discernible above 4000 rpm.

My buddy who is a super secrete squirrel black ops UAV helicopter engineer/fabricator, who is also the dude that let me borrow his 80, said it felt fuel related to him. I've got a spare fuel pump and fuel pressure regulator in my bins that I'm going to bench test and throw in tonight, other than that I'm thinking injectors or wiring?

I'd like to get a data logging oscilloscope for my iPad so I can log when each of the injectors are getting pulsed during driving. But since it doesn't happen under light load through the same RPM I doubt it's a wiring issue. I'm thinking it's a sticking / failing injector since low fuel pressure would probably result in more noticeable issues at the top end rather than down low.

Oh, and I have a text out to my bud who I sold my old 93 to just to see if I can borrow his AFM and rule that out.

How does my logic check with you guys? Thoughts? Am I missing anything?

Whats my next diagnostic step?
  • Verify Fuel Pressure at the rail? I'd need a remote gauge so I can see it while driving
  • Buy one injector and just move it down each cylinder to see if I find the dead one?
  • Replace the fuel filter (50k on this one)
 
SmokingRocks said:
Bench tested AFM per the FSM, all tests passed except for the air temp test but it was JUST out of the ohm range. This wouldn't cause my issue because it still is providing a value to the FSM which is within range, so if anything it's just telling the ECU the temp is a bit off from what it actually is
Click to expand...


There were two error codes related to the AFM and your tests verify a problem. It seems kind of self defeating to ignore that and assuming is not the problem. By design error codes don't get generated for trivial problems.
 
True, I plan on checking it against my buddies. However, the codes for the afm have only come up once and it tested fine outside of a slight variance at 140 degrees on the IAT. Additional faults should throw a code, which it hasn't. That said I'm not ruling it out I just think it's less likely the root of the issue.
 
Fuel Pump and Fuel Pressure Regulator swapped with spares, No Change. I have a play date tomorrow at noon to try Ben's AFM.

Also my Water pump has decided to start leaking, so this is going well.
 
jonheld said:
Sort of.
There is no feedback to the distributor from the ECU. The distributor is simply supplying 2 sets of tach pulses to the ECU which it processes according to its programming. Timing will depend on throttle position, knock sensors (if so equipped), AFM input, etc., but it is all done by the ECU.
Again, the distributor does not change or alter timing in any way.

On the 3FE, the crank position sensor was one of the tach pulses in the distributor. On the 1FZ-FE (I think both US spec versions) there is a separate crank position sensor that the ECU uses to reference timing.

Check that, the ECU uses the camshaft position sensor (one of the tack pulses) in the distributor to reference timing on the 1FZ, just like the 3FE. The crank sensor monitors RPM according to the FSM.
Click to expand...
OK glad you have his issue figured out.
 
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You made mention you swapped rotor, cap, wires but did you change plugs? I have had a plug cause higher RPM misfires but I think a code would be present.

Did you check the fuel pick up sock?

I think the AFM warrants further checks. If the temp reading is off the fuel mixture cannot be correct. I don't know the answer but I would check and see where the AFM gets it's temperature signal from and check that out.
 
MoJ said:
Have you pulled the plugs to inspect?
Click to expand...
SmokingRocks said:
Midday update:
  • Swapped over distributor - NO CHANGE
  • Swapped over Ignitor - NO CHANGE
So to date, I've done the following:
  1. Cleaned all grounds and + terminals
  2. Swapped ECU with my Spare
  3. Swapped Wires, Distributor Cap, Rotor with my Spares
  4. Swapped Coil with my spare
  5. Checked the AFM per the FSM and it passed every test (see post for info)
  6. Set timing back to 5 degrees
  7. Tested Fuel Pump Voltage at the pump, noted it was low on high flow, hot-wired to get 13+ volts to it at high flow. NO CHANGE
  8. Check Engine Codes have not returned since the original post
With everything above checking out I think it's safe to say the issue isn't in the ignition side. Here's some more info that we noted while testing it today:

The stumble happens under 3/4 to full throttle (load) more noticeably / harsher at 2500 - 3000 then less harsh but still noticeable at 3000-4000, and not discernible above 4000 rpm.

My buddy who is a super secrete squirrel black ops UAV helicopter engineer/fabricator, who is also the dude that let me borrow his 80, said it felt fuel related to him. I've got a spare fuel pump and fuel pressure regulator in my bins that I'm going to bench test and throw in tonight, other than that I'm thinking injectors or wiring?

I'd like to get a data logging oscilloscope for my iPad so I can log when each of the injectors are getting pulsed during driving. But since it doesn't happen under light load through the same RPM I doubt it's a wiring issue. I'm thinking it's a sticking / failing injector since low fuel pressure would probably result in more noticeable issues at the top end rather than down low.

Oh, and I have a text out to my bud who I sold my old 93 to just to see if I can borrow his AFM and rule that out.

How does my logic check with you guys? Thoughts? Am I missing anything?

Whats my next diagnostic step?
  • Verify Fuel Pressure at the rail? I'd need a remote gauge so I can see it while driving
  • Buy one injector and just move it down each cylinder to see if I find the dead one?
  • Replace the fuel filter (50k on this one)
Click to expand...
Maybe a long shot, but is it worth confirming throttle position sensor input vs. output? Or swapping in a known good one?
 
No forced induction on your rig right? I devoured a brand new set of spark plugs in 4k miles, supercharged, with the timing advanced to 4*.
 
Similar issue in this post:
forum.ih8mud.com

Hesitation at 2000 rpm 3fe

forum.ih8mud.com forum.ih8mud.com
Intermittent problem
truck runs great nice power....then decides to start hesitating from 2000rpm to 2500 rpm sometimes a backfire..... then takes off like a rocket once it hits about 2500 rpm.
also when this hesitation starts it will start idling badly.
it will do this if cold or hot.....

things checked
1. TPS....ok
2. IAC....ok
3. MAF....ok
4. O2.....ok
5. all sensors on water pump replaced...
6. all vacuum leaks fixed.... (Ed: but maybe not)
NO CODES CEL flashes like it should with no codes
i have FSM and have been going through them one at a time.
when it wants to run nice it runs perfect like new truck.....

============

UPDATE:
Problem found and repaired
IAC valve has rubber 0 ring gasket
Gasket was hard and brittle not sealing causing a intermittent vacuum leak.
Whew!
My 3fe runs like new.
Such a great feeling. Thank you all for your very appreciated posts.
 
thanks but the IAC gasket would only affect idle, as soon as the throttle body is opened and the vacuum is dropped the IAC has no effect. Unless there is aa huge amount of unmetered air coming in, but if that was the case the engine wouldn't idle well, which mine does.
 
Check your grounds.
There are several in different places.
Like from valve cover to firewall, intake to firewall, battery minus to fender, coil (igniter) to engine block, etc.
If in doubt, run a temporary one anyway to see if it helps. Some times a bad ground can cause all sorts of strange things to happen.
If there's a cluster of ring lugs, remove the bolt/screw, clean lugs with scotchbrite, add dielectric grease and retighten.
Good luck!
 
blkprj80 said:
Check your grounds.
There are several in different places.
Like from valve cover to firewall, intake to firewall, battery minus to fender, coil (igniter) to engine block, etc.
If in doubt, run a temporary one anyway to see if it helps. Some times a bad ground can cause all sorts of strange things to happen.
If there's a cluster of ring lugs, remove the bolt/screw, clean lugs with scotchbrite, add dielectric grease and retighten.
Good luck!
Click to expand...

1st thing I did! ^

Is there any way I can lock the rig into open loop? This would help me ID if it's a sensor problem or mechanical issue.
 
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