Calling all you Diagnostic Gurus | SOLVED Stumbling on hard acceleration THANKS EVERYONE (1 Viewer)

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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SOLVED: The problem traced back to an intermittent ground issue with the main engine harness, I built a temporary bypass harness for the fuel injectors until I can get a new main engine harness.

Read the entire thread for the diagnostic journey. Oscilloscope diagnostic techniques were used to track down this issue. I highly recommend getting one, this
Hantek 2 in 1 meter is an excellent unit and has the added benefit of being a multimeter and an oscilloscope. Beware of the cheaper units, it's almost impossible to get a quality oscilloscope for under $100.

Rig
Heavily modified 1993 FZJ 80
50,000mi on fully rebuilt engine
250,000 on chassis
PAIR removed
EGR disabled

Issue:
Over the past half a year (2,000mi) I have noticed a hesitation, like a misfire, between 2000rpm and 4800rpm, under full load. It's more noticeable in the higher gears when the engine loaded and taking longer to get through that rev range. At first, I thought it was detonation so I added premium fuel and when home checked the timing. The timing was still at 8 degrees advanced (no change from rebuild).

Then I checked the codes (the CEL was not illuminated during normal mode):
13 RPM signal lost when the engine revs above 1000rpm
24 Intake Air Temp Sensor Fault | Open or short in THA circuit for more than .5 seconds
31 Volume Air Flow Meter | Open circuit between one of two circuits in the AFM below 1500rpm

So straight away codes 24 and 31 shouldn't affect off idle running based on my understanding of what these sensors are providing.

What I've done / Checked:
  1. Removed the AFM, Cleaned all connectors thoroughly
  2. 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.
  3. Tested the resistance between the AFM connector and the ECU <0.4 Ω
  4. Cleaned all of the connectors on the distributor
  5. Tested the resistance between the RPM signal wire from the distributor to the ECU <0.9 Ω
  6. Replaced the distributor cap, rotor, wires, and plugs
  7. Replaced the ECU with my spare
So obviously since I swapped out the ECU the codes are gone, however, after a short drive, the issue is still there. So what am I left with?
  • o2 Sensors? | They aren't that old and that would probably trigger a more direct code right?
  • AFM is truly bad | Hard to believe
  • Problem with Fuel Delivery | more likely than the first two, probably wouldn't trigger a CEL code, BUT after 4800rpm the issue clears up (or perhaps the speed of the engine begins to hide the symptom at this point) additionally if it's a delivery issue wouldn't it get worse at higher RPM?
  • An issue with the ignition side/control | Low hanging fruit has already been replaced by denso/ngk stuff. Could be the Coil or control module???
The last thing to note is that when I checked my timing tonight I noticed my timing light was 'misfiring'. I had never noticed this happen before with this light, but I've heard of it happening so I guess I'll cross-check it on one of my other cars tomorrow. But it was like: blink-blink-blink-blink-_____-blink-______-blink-blink-blink-blink-_____-blink-blink I tested close to the cap, the pick up was pointing the correct way.

Really trying to figure this one out, so I'm calling on you guys to help me out!
 
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Under full load you should be running off of the afm in open loop power enrichment mode and not the o2 sensors. This also would put a heavy load on the fuel pump. You said you have 50k on rebuilt engine and issue has only been happening for 2k miles or so. So it's unlikely a issue with the rebuild and more likely an issue with a older possibly original component. I am not super familiar with obd1 1fz motors. But my gut feeling from what you tell me makes me lean toward the distributor is an issue and the timing isn't being advanced correctly. Perhaps the magnetic pickup isn't working right in the distributor or their is some shaft play. It is my personal belief that with pre OBD2 vehicles that installing a wide band air fuel ratio gauge can come in awfully handy when issues pop up. Also being able to monitor ecu live data is helpful to see what the ecu is seeing.
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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Thanks @White Stripe. So I have already replaced the cap, rotor, and wires. I guess I could check the shaft for play and make sure it's correctly oriented.. What else can I check?
 
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Thanks @White Stripe. So I have already replaced the cap, rotor, and wires. I guess I could check the shaft for play and make sure it's correctly oriented.. What else can I check?
I believe some of the toyota distributors don't advance correctly when they malfunction, I don't know why, but just trying to help point you in a direction of research. The AFM's are pretty finicky, doesn't take much for one to cause issues as well. You could try adjusting the clock spring in the AFM richer to see if that helps.
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
Joined
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Messages
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I believe some of the toyota distributors don't advance correctly when they malfunction, I don't know why, but just trying to help point you in a direction of research. The AFM's are pretty finicky, doesn't take much for one to cause issues as well. You could try adjusting the clock spring in the AFM richer to see if that helps.

Good info I'll take every drop! The AFM was within spec for all of the bench test noted in the FSM (below) with the only variance being the intake air temp.

I tested the intake air temp resistance (Test 5-7 below) with a hair dryer and a fluke temp probe placed right in front of the AFM probe.
The results were:
2.67 kΩ @ 68*F
1.35 kΩ @ 104*F
0.875 kΩ @ 140*F

Thats close enough to chaulk up to margin of error.
1607472366379.png


Today I tested the voltage at the Fuel Pump while driving, the results were interesting.

7.3-8.08v @ Low Flow
11.3-12.1 @ High Flow

It idled right at 8v then on tip in it would drop to 7.3 - 7.5v, I'm curious how many amps the pump is drawing. The high voltage seem waaay low, that should be pretty much alternator voltage right?!

The power path at full flow for the pump is this:
15a EFI Fuse --> EFI Main Relay --> Circuit Opening Relay --> Fuel Pump Relay --> Fuel Pump

I'm going to clean the grounds, battery terminals, alternator terminals and retest it. Might even put a bypass test line in that I can hit with a button to see if it affects a change. Low flow actually fits the symptoms.
 
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The timing light misfiring is a huge clue. They are silly simple tools and voltage though the plug wire is what trips the light to strobe.

Does the strobe misfire on cylinders other than 1?
Obviously you can't take a timing reading, but just point it at the ground and see if the blink is regular or if it picks up gaps on the other plugs too.

Could it be a flaky igniter ground?
 
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SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
Joined
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Messages
3,432
Location
Colorado
The timing light misfiring is a huge clue. They are silly simple tools and voltage though the plug wire is what trips the light to strobe.

Does the strobe misfire on cylinders other than 1?
Obviously you can't take a timing reading, but just point it at the ground and see if the blink is regular or if it picks up gaps on the other plugs too.

Could it be a flaky igniter ground?
I must have been crosseyed last night because I had the pickup facing the wrong direction, contrary to what I said. I've retested the light with the pickup facing the right direction and it flashes uniformly now.

That being said, I MAY HAVE FIGURED IT OUT and it has to do with the fuel pump voltage. Standby got to clean up the shop and take a shower then I will share my findings.
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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Ok, so tonight I wanted to see what my fuel pump was up to, so after monitoring the voltage at the pump (listed two post up) I noticed that both voltages were pretty low. On high it was regularly in the 11.5v region, way off the 13.8 the alternator was chugging out. I found this article which was very interesting in regards to the output of fuel pumps when they are not getting full voltage.

So I took the battery out, wire-brushed all the terminals and grounds, body grounds, frame grounds, I removed the center console and wire brushed that ground (since that's where the fuel pump grounds to). I also cleaned the positive terminals all the way to the alternator.

The result of the cleaning was:
8.03 - 8.88v Low Flow (Improvement of about 1 volt over last test)
12.11 - 12.67v High Flow (Improvement of about 1 volt over last test)

Test drive demonstrated the hesitation was still there, perhaps less noticable but still there. So I went back to the garage and rigged up my fluke to monitor when the low to high switch happens and I wired up a "Turbo" switch so I could send direct battery voltage to the pump when it went into high flow mode. 2nd Test Drive Results:

8.03 - 8.88v Low Flow (No change)
13.5-13.7v High Flow (2+ volt increase over baseline)

The hesitation was no longer present while I was in turbo mode, if I turned the switch off the hesitation would return. I don't like to claim an early victory, so I will need to test this more but it seems like I may have found the issue. Now I need to backtrace the circuit and figure out why there is such a drastic voltage drop through the positive side. If nothing comes up and its just a factor of being an old ass rig then I'll consider wiring in direct battery power to the Fuel Pump Relay since I know thats new and the pathway between that and the pump is low resistance.

Heres a fun photo of my "testing rig" and sweet shifter mounted "Turbo" button.
IMG-4019.jpg
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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Problem persists. This is why I try not to get excited when I think I’ve figured something out.

so now I know the fuel pump is pumping, I guess I should check the fuel pressure to verify the health of the pump, which I’ll do, but it’s looking like the problem is back on the ignition side, unless it’s an injector.

need some ideas on what test I should preform next.
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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Thanks, my tank is squeaky clean. Checked it last night.

I just got home from a job walk and rechecked the wires with my timing light. And one and two were blinking twice as fast as the others. So it looks like they are arcing out. These NGK wires are less than a month old so I just assumed they'd be ok, maybe I don't have the proper separation in the run?

I'm going to feel really dumb when I find out this is the issue...
 
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Thanks, my tank is squeaky clean. Checked it last night.

I just got home from a job walk and rechecked the wires with my timing light. And one and two were blinking twice as fast as the others. So it looks like they are arcing out. These NGK wires are less than a month old so I just assumed they'd be ok, maybe I don't have the proper separation in the run?

I'm going to feel really dumb when I find out this is the issue...
Wait until it's dark, then drive your truck until it's good and warm. Remove the spark plug loom covers on the VC.

Go to an area that is VERY dark (If you do this inside your garage, you must have a vent for your exhaust) and run your engine. Many times you can see the plug wires arcing to the block or to each other during the conditions you are describing. It is more likely to occur when the wires are warm and the resistance is higher. It also does it more under load and higher RPM.

This was my first thought based on your description, but I discounted it based on the fact that you said new cap/rotor/wires. I assumed Toyota, but they are not.

My LC is the first vehicle I have ever owned that spits out aftermarket parts like cap/rotor/plug wires. It does NOT like them. I went back to OEM and problems disappeared. I thought it was BS too, but I've seen it with my own eyes.

It's worth a shot.

I have done this a lot on old cars and trucks to eliminate ignition problems.
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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Thanks guys,

Yep, I'm very familiar with how these rigs reject cheap replacement parts, I figured since NGK did make factory parts for toyota that they'd be fine, guess not. I've got shelves full of spare parts so I just pulled out the set of wires I had on it when it blew the HG. They are either OEM or Denso and for some reason, I'm missing one of them.....

Tonight I'm going to swap those wires on and swap the cap with one from my parts bin. If I can find anything else ignition-related in there I'll probably swap those in too, this is why it's good to keep parts replaced as PM.

I'm also going to run through all of the on-vehicle checks listed in the fsm section attached. At this point, I highly suspect the distributor and to a slightly lesser level the igniter / Ignition Control Module.

Since one of my codes was related to the distributor it seems to be more probable.
 

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SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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The saga continues.

Tonight I swapped the wires, ignition coil and distributor cap with my spares after bench testing them per the FSM, made sure to install the wires with the routing per the FSM as well. Everything was within spec. I pulled the distributor and bench tested it per the following:

1607576885599.png

Gap test:
NE pick up had the outter edge at 0.4mm and the gap got larger as it went towards the back of the casing
G1 Pick Up: 0.32mm
G2 Pick Up: 0.4mm

There was some varnish on them from misc. oil leakage over time so I cleaned them up and reinstalled the unit, warmed the engine set timing to 5* advanced (pulled it back from 8*)

Next test:
1607576788719.png

Cold Resistance Test, all readings were within tollerance.

Test Drive: no change, heistation is still there. I've dropped a line to my good buddy who I sold my other 93' to just to see if he's around this weekend. If he is then I'll go to his shop and pull his dizy to see if it solves the issue, if not then I'll move to the ignigter. If it's none of those then I need to look back on the fuel side of the equation. Am I missing anything guys?
 
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I think swapping distributors is a good idea. Testing fuel pressure also I think is a good idea. How old are your injectors?
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
Joined
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I think swapping distributors is a good idea. Testing fuel pressure also I think is a good idea. How old are your injectors?
Injectors are original I believe. When I did my HG engine rebuild I had them cleaned and flow matched. They mentioned at the time that all of them leaked down.

this one has been a frustrating diagnosis because I’m so torn on which leg of the combustion triangle I need to focus on. AND how I can test them accurately.
 

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