Odd Acceleration Issue & Occasional Pulsing Idle

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If I had more information on which sensors the ECU is evaluating to determine when to trigger the FPR I could narrow down my search for the delayed acceleration issue. But this is all the FSM gives me
View attachment 2974547

Both banks tie in after the cats, I mean I can scope the O2 sensors and determine the A/F Ratio based on voltage seen, since Lambda is 450mv which = 14.7:1 A/F Ratio.
Well it sounds like a afm flap issue to me personally. In open loop it's running strictly off of the afm until the o2 warms up enough to work. Also check all your vacuum hoses.
The wideband will help in the future to tell if a fuel pump is going out or if you have a ignition problem or the o2 is bad or if the afm is making the motor run too rich or lean-stuff like that. In other words it will really give you accurate and important information better than narrow band will. I would weld a bung in each bank before the cats and just run it in one of the 2 banks and put a plug in the other bung.If a issue arrises you can swap it to the other bank and compare the 2. A lot of people are unwilling to do this. But on my personal obd 1 cruiser it's really helped me out find issues big or small and it's easy to do. Wide band kits are cheap these days. I got a ebay kit and it works great. It's hard to get accross how useful the afr is on a obd1 cruiser. I'm probably starting to sound crazy endorsing a wideband setup though so I'll shut up now lol.
 

SmokingRocks

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I really have a hard time believing it's the AFM since I recently ohm'd it, but I'll put it on the list to check. I guess reading the Diagnostic code section regarding the AFM there is a possibility of it not triggering a CEL yet still causing the issue.

So the 96 FSM gives some more insight as to the ECU's logic for controlling the FPR, now it could be completely different from the OBD1 93 ECU but usually, that's not the case, however due to the changes from the AFM to the MAF this might be off base. According to the OBD 2 FSM the Fuel Pump Control Circuit only shows the FPR being triggered closed (closed means low flow) when there is no STA (starting) signal and or the crankshaft position sensor providing the engine RPM signal to the NE port indicates idle speed or light loads engine speed.

But that can't be all the logic since the engine RPM's can be low but the load can be high....

DI-115.jpg


This is the diagram of the same circuit as shown in the 94 FSM, I'm curious as to what's going on with the logic in the circuit opening relay. Will need to study that a bit more.
Screenshot 2022-04-07 155656.jpg
 
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I really have a hard time believing it's the AFM since I recently ohm'd it, but I'll put it on the list to check. I guess reading the Diagnostic code section regarding the AFM there is a possibility of it not triggering a CEL yet still causing the issue.

So the 96 FSM gives some more insight as to the ECU's logic for controlling the FPR, now it could be completely different from the OBD1 93 ECU but usually, that's not the case, however due to the changes from the AFM to the MAF this might be off base. According to the OBD 2 FSM the Fuel Pump Control Circuit only shows the FPR being triggered closed (closed means low flow) when there is no STA (starting) signal and or the crankshaft position sensor providing the engine RPM signal to the NE port indicates idle speed or light loads engine speed.

But that can't be all the logic since the engine RPM's can be low but the load can be high....

View attachment 2974574
My thought was the flapper door on the afm was getting gummed up when cold. It sounds like your on the right track and will get it figured out pretty soon. Hopefully it's something simple.
 

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THanks, it's not a problem that is leaving me stranded, it's just annoying. I wish that I could find a schematic of the OBD1 1FZ-Fe ECU's circuits so I could trace the logic, the 96 FSM gives almost enough of this to be helpful but that didn't exist in the 93-94 fsm..

These rigs were built during a time when all this electronic control was pretty simple, it's just a lot of tiny relays (transistors), controlled by simple circuits.

Definitely wouldn't feel comfortable doing this on my A7


I think I'm just going to shotgun in some of my spares to see if there are any changes, that'll switch out the: Circuit Opening Relay, Fuel Pump Relay, ECU, TPS.
 
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The OBDI is definitely different. As you can see the circuit relay gets grounded through the AFM which is accomplished by the mechanical flapper door. OBDII as a MAF so doesn't have this feature .

However, the FPR in the MAF grounds as soon as the door moves. If that wasn't moving the truck wouldn't start at all. If you remove the AFM from the air cleaner you can watch it move realtime while the engine is running. Unless it's slamming closed it's not shutting fuel off. It will cause it to tapper off but that's how it works.

Frank
 

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Even a tiny movement of the AFM triggers the FP. Key on, move the AFM flapper, you should hear the hiss of fuel commence. If you install a fuel pressure gauge you should have the requisite PSI. If that hiss doesn't occur, the truck won't run. The FP itself is Boolean on/off with pressure controlled by the mechanical regulator at the forward part of the fuel rail. There is some vacuum modulation of the fuel pressure though I forget exactly how that changes it. If you start the truck, you'll see the flapper door move quite a bit and it will pulse with the change in idle as it should.

Note, if you do start the truck and the idle is surging, try manually moving the AFM door inward some. If the idle smoothens, at least you know you have a lean condition and we can work from there. The AFM is also easily testable and so I'd do that as well just to rule it out.

Frank
This is great info, I’m just rereading everything and realized I missed some important statements you made regarding how these circuits operate.

I’ll for sure try moving the AFM flapper next time to rule it out. Check off the low hanging fruit.

Also can you share your spreadsheet? And what scope did you get, pico?
 
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Shoot I forgot to upload it last night. We went to Journey and Toto so got a bit distracted. I'll do that tonight.

I picked this one up. It's a stand alone but figured since I don't always have a tablet or comp on the trail it might make sense to get a stand alone.

Amazon product

Frank
 
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Had to fix the hyperlinks but check it out and let me know if you find any errors or improvements. Maybe we can make this a living document for the benefit of all.

1FZE Troubleshooting Template
 

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So I took the IAC valve off to clean it and I ran the FSM's test on it as detailed below. The B1 --> S, S3 checked out ok at 26 Ω. The B2--> S2, S4 came in at 49 Ω, the test temp was about 72° F, so close enough. Well, I didn't think much about it and cleaned the rest of the valve and reinstalled it last night.

Went to start the rig today and its apparent that the IAC valve isn't doing anything. I even have my air compressor tied into the ECU to trigger the AC idle up feature which the IAC valve performs and it's completely unresponsive to that input now.

Screen Shot 2022-04-09 at 6.25.45 PM.png
 

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So I scoped S3 from the ISC Valve and I switched on my Air Pump circuit several times, which as stated previously triggers the ECU to bump up the idle via the AC input port. And in the scope, we can clearly see that the signal is being sent out to the ISC. I also checked continuity from the ECU to the ISC and it's fine, and both B1 & B2 have voltage when the key is on. So looks like the ISC valve is fubar'd.

Screen Shot 2022-04-09 at 7.30.40 PM.png
 
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What are those pulses? Are they to the ISC?
 

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Yea so this takes some explaining.

I don’t have A/c in this rig, and I wanted to add an idle bump up for when the air compressor is turned on to help the alternator get to an rpm where it can produce more. I read that when the A/C is switched on the ECU sees this and will bump up the throttle in response (it does this when you shift into gear as well). So I tied in my air compressor switch to the A/C on port in the ECU. And it’s worked fine for years.

So it’s an easy test to see if the ISC Valve is actually moving, the pulses on the screen are when I activated the air compressor switch and the ECU tried to idle up. I hit the switch twice, those two groups are the signals going out from the ecu to the ISC.
 
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Typically the ac won't turn on unless the pressure sensor reports enough refrigerant. However, when you start it, does it idle high and come down to a resting idle?
 

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I don’t have ac. I just used the A/C port on the ECU to trigger an idle up. So it’s an easy way to see if the ECU is sending signals out to the ISC, which it is.
 
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Good tip. Did you get a chance to measure the O2 sensor voltages, OX1 and OX2?

Frank
 
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Sounds good. I replaced my bad O2 sensor and it cured my truck... this time. It was a Denso sensor with about 1000 miles on it that went bad. I put in Delphis, found a good deal on 'em, the truck seems happy and runs much, much better.

Frank
 

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IAC (ISC) signal testing. Again the signals sent to the ISC valve are present and working. In this test I expect to see S1-S4 pulse to ground, and all do.

ISC 1 Blue
ISC 3 Yellow
ISC - S1 & S3.png


ISC 2 Red
ISC 4 Blue
ISC | S1 & S3.png
 

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