bluetruck

Hi all. Purchased this truck 4 years ago with a newly rebuilt engine and it has run great. Until about a year ago it started on half a crank. Can't recall when it began but it now takes four cranks, then ALWAYS starts on a half crank on the second try. Perfect every time, cold or warm, winter or summer. Once started runs great, except for intermittent rough idle.

So far: new plugs, cap and rotor; fuel filter. checked all fuses;
Engine starts ok and dies with AFM unplugged (does this prove AFM is ok? What's a good test?)
TPS tests a bit out of range, but why should that effect startup?

Fuel pump does NOT turn on with key in ON position (don't know if that's normal) so priming doesn't happen with key on for a few seconds, as has been sugggested.
It fires right up with jumper FP-B+ OR a shot of carb cleaner into the throttle body.

Would it be a horrible mistake to leave the jumper permanently in place?

Been living with this problem for about a year, Doesn't change much with cold/hot weather or when engine is warmed up.
Hope someone can help me understand what to test, how to test it and in what order.

scope103

The engine SHOULD die with the VAF unplugged, but the VAF does a lot of things, so that isn't a "test" of anything.

Normal.

Only if you worry about being burned alive.

This gets explained about 3 times a week here, so a little searching might have helped you.

The Fuel pump is powered by the COR (Circuit Opening Relay). The COR has two windings; one pulls it closed with the key to STArt (not just key-on), the other pulls it closed when a switch in the VAF closes due to air flow. If you get in an accident that breaks a fuel line, as soon as the engine stops pulling air the fuel pump shuts off. If you leave the jumper in (which bypasses the COR), the fuel will just keep spraying.

I'm going to guess you have a problem in the STArt-COR circuit. The COR doesn't close with STArt, but it does after you crank it enough to close the switch in the COR. Pull out the Starter Relay (or disconnect the solenoid lead from the starter -- the relay is much easier to get to) to keep the starter from turning. Put your multimeter between FP and ground (voltage). Turn the key to ON (you should get 0v), then to STArt (you should get 12v). If you don't get 12v, the problem is probably in the COR (or the wiring). Pull out the COR (behind the glove box) and test it: http://web.archive.org/web/201003261...96circuito.pdf (They're expensive; don't replace it just out of laziness.)

bluetruck

Looks like there's 12v in START and 0v in ON. Since it runs well it would seem that the FP circuit and pump are functional.
Seems to start somewhat easier since it's been dosed a few times with carb cleaner into the intake. It's somewhat dirty in there but the throttle plate and body looks clean. Hope nothing got hurt with spraying.
Starts better but still not back to it's half crank and fire.
Should get some time over the weekend to experiment. Will post follow up. Any suggestions welcome.
Thanks hugely for the help!

(Still weighing the question about being burned alive. Might be preferable to tracking down an elusive problem.)

RAD4Runner

As Scope suggests above...
Also... "1994 22re Pickup"...
Always indicate model-year-engine-TRANSMISSION-trim when you ask for help. Better yet, put it on your signature like I did.

PRIMING:
I think you can prime, by the following:
1) Transmission in neutral.
2) Foot off clutch, so clutch safety switch stays open so starter will not energize,
3) Clutch Safety Cancel switch NOT engaged so starter relay will not energize,
4) Ignition to START position. You will hear the C.O.R. click behind the glove compartment, this turns the fuel pump on. Wait a couple of seconds. (Experiment with how long to hold the key before step 5).
5) Finally, step on clutch OR activate Clutch Safety Cancel to energize starter relay and the rest of the cranking system.

MONITOR FUEL PRESSURE
To eliminate doubt on fuel pressure some of us installed fuel pressure gage piggybacked on the CSI

Thommo Thompson

It is true that the wearing out of the piston rings and or the cylinder bores increases (lengthens) the startup time. A good compression test result would rule this out.
Anything less than about 145 PSI and I'd be just saying it's just a bit worn out.
good compression really helps start a cold motor, and when cold, a worn motor suffers from it's weak compression the most.

wyoming9

iTrader: (1)

Don`t know about the compression my 22re I can turn with one hand on the crank pulley with the plugs in.

Starts right up.

I would check your Circuit Opening relay

Burning is not fun

bluetruck

UPDATE: Well, small progress, but progress.

Noticed it started better with the MAF flap held open for start. Improvement. Opened and cleaned the potentiometer with a cuetip.
Now fires well on the 4th crank.
Jumping FP-B+ seems the only method so far that gets it to fire on the first crank, as it used to. This appears to point somewhere, but it's unclear,

Timing seems good. Air filter is new (but it's a cheap one). New fuel filter.

Somehow I've misunderstood this. No pump noise with clutch up and STArt. Can hear a relay in dash near steering column. Same starting result.

Thanks to all for your insight. Will delve some more Sunday night.

yota tay

Battery or starter?

old87yota

Nevermind.

yota tay

Please tell me you have a new battery.

yota tay

What​​​​​​​ you say is true. But a weak battery can cause havoc. Been there.

Thommo Thompson

OK u may have an issue ith the pump not starting until tge vfm is really pushing on the switch.
I thi be there might be a bit of missinformation here, the fuel pump in this car simply doesn't turn on unless there is air being sucked by tge engine. There is no 3 -5 second timed priming relay in these things. It only gets power if 3 relays are on,
1. Switch in VAFM
2. EFI main relay
3. Circuit opening relay
I belive it never can turn on without the engine sucking air. That tells me it's likely that the switch in the vfm is just old and worn, or possibly just suddenly bent or snapped. Probably plastic involved seeing as the VAFM box is plastic.

Co_94_PU

iTrader: (-1)

Pushing the flap open does the same as the fuel pump jumper. Your problem lays in the pump relay, the wiring to the tank, or the fuel pump.

Check voltage drop at the tank, and current flow.

If you haven't done so already pressure test would rule out a bad filter, pump sock, and anti drain back valve.

Thommo Thompson

Co 94. Are u discounting what I suggested to be the potential cause? If so I don't quite understand ur point, can u please elaborate because u may have a good point but I don't understand it.

Co_94_PU

iTrader: (-1)

He says they swabbed/cleaned out the afm. It's possible they didn't clean this part, but it's not likely to pick up much or bend. More likely there would be a bad wire in the plug to the vafm, or a worn/dirty or spread terminal and just from unplugging and plugging it in it closed the circuit.

Anyway..

This is a simple Reed switch, it carries very little current, is in a sealed housing, and doesn't touch anything it's free standing in the housing with clearances on all sides. It's very unlikely to bend or collact any debris, it is also a cast aluminium housing.

In the case of these cor equipped Toyota the cor is the fuel pump relay, it has one high current feed for the pump and two control inputs, one is the vafm Reed switch, the second connects to the st1 signal from the ignition switch.

FP in the diagnostics circuit is spliced down stream of the cor.

So you test the startup and running current of the fuel pump, this identifies failing brushes, bad windings, clogged lines/filters, and may indicate bad wiring (high resistance) as the cause. The voltage drop test, which is easier/safer to do by the way, will rule out a bad feed wire, relay contacts, and bad grounding, leaving you pretty certain it needs a new pump.

They have reported no excess voltage on the positive side already (voltage reading on FP while cranking). So bad ground, ground wire to apron, or poor ground at the apron to battery. Or a bad pump.

​​​​​​​You still want to check the current, voltage and pressure before you recommend getting elbow deep into a fuel tank, cause that's a bad rabbit hole to go down you are going to find flakey rust scale, corrosion on lines, and corrosion on wires.

wallytoo

iTrader: (1)

wallytoo

iTrader: (1)

rancherman

This seems to be a 'timed' issue. OP states quite clearly that the truck takes several cranks to get it lit. AFTER IT'S SAT FOR SOME TIME. After it's run, restarts are 'normal'. Although, 4 revolutions to get any engine started, especially cold, doesn't seem too 'off'.

I'd lean on either he has a bleed back issue, from either a 24 YO pump, lines, connections.... huge vacuum in the tank @ last shut down... or has a lazy/sticky vfm. It might take an extra second to get it off the 'off' peg, and subsequent restarts are easier because it hasn't returned yet 'home'.
Put a gauge on to see how long it holds pressure after shutdown, and how quick pressure builds during the starting procedure

RAD4Runner

https://www.yotatech.com/forums/f199...l#post52312190

Thommo Thompson

Hmm I didn't read OPs post propperly. He said there was 12 v to pump when ignition was in start position, so that start prime system alone should override any issues with the VAFM switch coming on a bit late.
its sounding more and more just like there may have been some changes made to this trucks wiring. OP sais he can not hear the pump running when in start position, but when probed with a voltmeter it reads 12v+ going to the fuel pump when the key is in start position.
That kinda suggests maybe someone has put the negative side of the fuel pump through a switch or relay that connects the negative side to earth/ground only when engine is running. Or something to similar effect.
OP can u test that 12 volts again in the start position, with the positive probe on the fuel pump connector positive, and the negative probe on the negative wire in the fuel pump connector, but this time leave the starter solenoid connected and let it crank.
I feel either some rewiring may have been performed or the starter solenoid circuit might be shorting, or sucking lots of juice.
That is of course, if u have carefuly listened in the filler neck and confirmed 12 v at start position but no pump running.
if anyone disagrees with my analysis, they don't understand my point because I haven't been clear enough. So if that's the case, let me know and I'll try to elaborate further.

Also, side note, when I say the fuel pump can't run without the motor running, I'm not sure a valid argument against that is a test probe jumper.