A little background first. Owned since new, 1992 SR5 Xtracab 4X4 pickup, Japanese made, 198+K miles. At around 100K miles, I had a Toyota dealership change the timing belt and new water pump. I replaced a fuel pump around the same time. In the last year and prior to current issue, truck started and would run. After driving a couple of minutes, it would just fall on its face, no acceleration. Sometimes it would come out of it on its own, sometimes I would have to pull over and restart it. After that it would run good for a long while and might or might not repeat the stumbling acceleration. I would also have problems with the starter until if finally just refused to start anymore. I replaced the starter and it works. Replaced starter, fuel pump, fuel filter, plugs, wires, distributor cap and rotor plus most of the vacuum lines. Wouldn't start. I checked the fuel pressure with a gauge and only had 30 psi and would go to zero immediately after shutting the fuel pump off. Replaced the fuel pump and now I have 45 psi and holds pressure after the fuel pump is shut off.

Right now it will crank but not start. All of the fuses check good. I hooked up the fuel pressure tester and showed 45 psi when I used the key to crank it. No start. Removed the #1 spark plug and cranked it and it had spark. Looked in the spark plug hole with a boroscope and the top of the piston was wet with gas. The only thing that I adjusted was the idle speed adjusting screw when it was previously running. Didn't determine where it was before I started adjusting. Idle had been high so I had reduced the idle speed. I've tried to start it with screw all the way in out to five turns out, trying to start it at each turn out. No start. Any suggestions on the idle screw setting?

Am I correct in stating that I don't have a VAF/COR circuit problem since I have fuel pressure on trying to start it with it with the key? I checked the distributor coil and ignitor coil and both checked good for ohms according the the FSM, thus a good spark. I checked the VAF for ohmic values, all checking good except for VC-E2 which measured about 900 ohms. But the truck ran previously, so I don't know about that. Haven't checked the throttle position sensor yet. Again, the truck ran previously.

Any suggestions on what to do next? Thanks in advance.

 

Remember that the COR has 2 halves to it. One half runs the fuel pump when cranking, the other half runs the fuel pump once the truck starts.
The second half is operated by the VAF vane being even slightly open. There is a switch in the VAF that applies ground to the COR to allow it to run the fuel pump. But only while the engine is running.
One thing you can try is to put the jumper in the test jack on the side of the engine fuse block, to run the fuel pump, and try to start the truck. If it starts and runs, the problem could be the "run" half of the COR, or the switch in the VAF. You said you ohmed that out, so my bet is the COR being bad.

You might also check the wiring between the VAF, and COR and ECU.

Definitely check the TPS alignment. There's a good chart of the ohm values that should be read out from the TPS in the FSM. There's also a very good "how-to" about the TPS alignment procedure.

Good luck, and keep us informed how things go for you.
Pat☺

 

Thanks, Pat. Same first name. I tried the jumper at the fuse box area, B+ to FP. No joy. Got run inside by thunderstorms. Hopefully I can get out there later or tomorrow AM and ring some of those wires out that you mentioned. No real trouble for 29 years so I guess it's my time in hell. Lucky that I have other vehicles for daily drivers.

 

I took out the COR and tested it on the bench with a 12vdc power supply. Both sides of it work correctly. When power (from start relay) is applied, the coil is energized and the contacts close to apply power to a load (fuel pump). At the same time power (from EFI main relay) is applied to the second coil (holding coil) in the COR and it is grounded through the VAF switch. When the start relay opens and removes power from the first coil, the holding coil continues to keep the COR contacts closed. I'm convinced the COR is not the problem.

I read out all the wires involving the VAF to the ECU/TPS/COR, the TPS to the ECU and VAF, and all of the COR pin-outs. All checked good.

I couldn't get to the pins of the TPS to read it out with the connector disconnected. I left the connector attached to the TPS and took my readings from the disconnected ECU connector. I got 0.847K ohms from VTA to E2. IDL to E2 was open at all settings. With the throttle wide open, VTA to E2 1.28K ohms. Didn't check VC to E2. I just ordered a TPS. Should get it early next week. Maybe it's just the adjustment, maybe not. At least I will have a new one. I plan on taking the throttle body off to install and adjust the TPS. Any tips about the water lines going to the TB. I wonder whose bright idea it was to run water to the TB.

 

Best tip I can think of about the water lines is: REPLACE THEM. Replace them ALL while you have the TB off. Think about how old they are. Rubber doesn't last forever. Most of them are pre-formed, and can get a little expensive, but think how long the originals lasted. Don't try to just run standard water hoses, like off the shelf lengths of hose cut to fit. You'll get kinks that block the flow.
When you go to remove the old hoses, you may need to cut them off. A cut lengthwise along the hose, where it's on the barb. Don't cut deeply enough to score the metal of the barb. The barb's metal is rather thin, and a score line could cause it to rupture in the future. Just down close to it, then peel the hose apart to remove it.
Clean the barbs they go onto thoroughly. They will probably have corrosion on them, and may need replacement. When you go to put the hose back on, coat the barb with a thin layer of Vaseline, or the silicone dielectric grease. It will let the hose slip on much more easily, and tend to prevent the rubber binding to the metal of the barbs as it's prone to do.

As to the TPS: The IDL - E2 being open at all settings. That's a telling problem. It might just be the TPS's adjustment. In any event, even with a new one, you will need to adjust the tps for the IDL setting. It's an important setting. Just need a feeler gauge to set it correctly. The procedure is in "THE Book".

Good luck!
Pat☺

 

It's almost certainly the adjustment.

Don't freak out about the feeler gauges and 3-digits of precision resistance measurement. All the IDL contact does is conduct with the throttle closed, not-conduct with the throttle open. But what's "open"? Toyota just defines it as more than 0.80mm. What's "conduct"? Again, defined to be less than 2300 ohms. http://web.archive.org/web/201108151...93throttle.pdf 9 times out of 10 you can just hook up your meter, and inch the adjustment back and forth until you see the resistance jump when the throttle is opened.

Ah, cmon. While I'm not an Automotive Engineer, it sure looks like the real engineers who designed your truck felt that drivability was improved by warming the throttle body. If you're smarter than those engineers, you can figure out a modification.

I don't see where you've checked the ignition timing (you'll need to get the TPS adjusted correctly to hit "base" timing). I also don't see that you've checked the ECT sensor.

 

The ECT sensor read about 1.9k ohms at OAT of 85F. Chart is not that accurate. I don't know how to check the timing without the engine running.

I'll try adjusting the TPS without taking the TB off.

Thanks for the help.

 

Ended up taking the TB off. Cleaned it up and tried adjusting the TPS. I got the IDL-E2 adjusted. Even used a feeler gauge since I had the TB off. VTA-E2 was 0.847K ohms. When I opened the throttle wide open, VTA-E2 showed an open as did VC-E2. The new TPS should be here by Tuesday.