Walrus

Long time listener, first time caller.

I bought a 1987 4Runner 22RE last year on the cheap for a father and son project and 4x4 rig. Got it running good, and drove it around for about 1000 happy miles. Threw on new tires, manual hubs, CB, and was getting ready to hit the trails. Four days before my first 4x4 trip, it dropped a valve guide. Needless to say, my trip was cancelled. I saved for a few months, and bought a new head and rebuild kit from engnbldr based on reviews on this forum (GREAT parts and customer service, A+ all the way, Thanks Ted and Todd). I honed the cylinders and replaced bearings, pistons, rings, head, cam, oil pump, water pump, and gaskets all following the FSM. Got the motor stuffed and got it running about a month ago and it ran great for about 300 miles. On an evening ride it started hesitating and acting like it was fuel starved. Any time I gave it more than ¼ gas pedal, or if it was under load, it would stumble and provide no power. It progressively got worse, and we limped the rig home at about 30 mph. I started troubleshooting, and so far I have done the following:
1) Changed fuel filter
2) Jumped the fuel pump to verify operation per FSM
3) Checked cam chain to verify it didn’t jump a tooth (it didn’t)
4) Verified the distributor was installed correctly
5) Checked all vacuum lines for proper routing and connections
6) Checked all wiring for connections and routing
7) Checked all grounds
8) Checked primary and secondary ignition coil resistance
9) Checked spark plug condition and gap
10) ISO HEET in the fuel tank
11) Swapped ECUs (had an extra)
12) Checked intake for leaks
13) swapped coil
The problem has continued and it will happen at no specific driving condition or mileage. At startup, I have always had to “prime” the fuel pump by turning the key to start and running the fuel pump (same as jumping the maintenance terminals). After a few minutes, the truck runs great. Then, about 15 mins later it starts to lose power. The truck will progressively get worse, to the point where it is providing no power at all. I pull over and shutdown and sit for a few minutes. Sometimes it starts right back up, and I can drive for miles; sometimes it acts up again right from the start.

I am kind of stumped here guys. Any ideas?

BTW, thanks for a great Forum; I will be posting more for sure. The amount of great info here has been very helpful.

Gamefreakgc

You're pretty thorough. In most cases, you would have found the issue by now.

The fact that it only shows the issue after 15 minutes of driving makes me think it's one of two things: overheating issue, or bad sensor (when engine gets hot, sensor fails).

Overheating is pretty easy to figure out. Does you temp gauge EVER move past half? Does it linger in the low range until 15 min and then start to move? If yes, you could have old/bad coolant, thermostat stuck shut or blockage.

The second possible culprit would be a sensor. Our truck's ECUs won't throw codes for half the sensors installed, so they can fail and you'd never know, you'll just notice a difference in how the truck runs.

Here's a diagram from the FSM that shows all the sensors involved in the MFI system (multiport fuel injection): http://personal.utulsa.edu/~nathan-b...23descript.pdf.

You'll need a multimeter to check the sensors accurately, as described in the FSM. If you haven't already, take a look at the MFI section: http://personal.utulsa.edu/~nathan-b...sm/engine.html.

The most likely culprit would be your Engine Coolant Temp. Sensor. These are known to go bad and cause a host of issues and it's hard to trace it back. Just pull it out from behind the engine (it's the smaller of the two identical plugs, the other is your Cold Start Injector Time Switch), I think it'll either be grey or green in color. Check it for corrosion, loose connection, or bad wiring. Mine broke in half when I went to check it. Make sure you do the multimeter test when the engine is cold so you can accurately measure it.

Other possible bad sensors would be your VAFM. The intake air temp sensor located inside could be failing.

There's others, but those are your most likely causes. Hope this helps ya.

gennro

Check your fuel pressure regulator on the fuel rail near the firewall. You will need a pressure guage of some sort to test it, but sounds like it is failing from you saying you have to prime the fuel pump to get the truck to start.

orbital02

X2 on gennro's comment. I also thought your knock sensor maybe bad... Have you verified your check engine light is working? The knock sensor is the only sensor I know that will put the truck in "limp" or "fail safe" mode.

wallytoo

iTrader: (1)

are those pages for an '87 that you linked to? i ask because my '87 doesn't have the same features. my ECU terminals aren't the same at all, either in terms of connection locations and # of terminals in the strip.

there are other differences, too.

87 seems to be a transition year. they have a lot of similarities to the 85 (same ECU terminals/arrangement), but have the diagnostic box on the inner passenger fender, which the 85 doesn't seem to have, but the runner for the above link does have. many of the resistance/voltage specifications are different between the two, so the correct data would be useful for diagnosing problems.

wally

Walrus

Thanks for the replies. I forgot to mention in my first post that I replaced the fuel pressure regulator. I am wondering if the vacuum line from the 4x4 VSV that operates the regulator is bad. Couldn't I just run the vacuum straight off the manifold to the regulator (I have manual 4x4 hubs)? If the vacuum is working to the regulator, how else would I be losing fuel pressure with no leaks in the system? I will check the knock/coolant sensors with the meter; all the wiring looks good.

I have asked around a bit at work, and some guys are thinking the fuel pump may be going bad once it heats up. Does that sound plausible?

I really appreciate the advice. I hope to troubleshoot more soon; work, family, and home projects have taken all my time lately.

xylicon

Interesting problem you said it starts losing power at 15 minutes and then gets progressively worse, have you looked into fuel vapor lock? Is your fuel tank venting properly? / Is the charcoal canister working properly?

Mr.Cheekers

Check the O2 sensor. I was having similar problems. I checked everything VAFM, coil, injectors , ECT. I got to the O2 and it ohmed out bad, lots of green corrosion in the connector. I am short on cash( new baby boy 10 days) so I cleaned the connectors with vinegar and soaked the business end in seafoam, wire brushed and blew it all out. When I replaced it and got extremely noticeable results ( night and day type).

I also swapped the coil injectors and the TPS with little to no effect.