307Yota

Newb here. I've used YotaTech as a guest many times in the past to help solve issues on other vehicles. I value this forum very much and I thank those that created the site. This time the search function hasn't delivered the results I'm looking for.

I am working on a friends 1993 Pickup. We rebuilt his engine because he dusted it badly. The intake tube just above the drivers side valve cover had a large hole in it. The compression was way down, but it ran, till the timing belt tensioner and idlers gave up, shucking the timing belt. We did the heads, rebuilt the bottom end, and assembled it as per instructions from the toyota manual. All of the sensors behind the plenum (coolant temp, bi-metallic switch, cold start timer) were replaced. Also replaced the ignitor at the same time as we had the ignitor code when it came in.

So now we have a freshly rebuilt engine that ran for about a month. As the weather got colder, the truck would not start. We couldn't duplicate the problem and it became a joke between us. If it's cold, I could start it. Not my friend. The cold start issue went away, and we heard that it was running better than when it was new.

A week later the truck will barely run once warm. I went out to pick it up (after searching here) and read about TPS sensor issues. Even though it was 30 degrees, the truck fired right up. As per prediction though, once warm, it wouldn't run very well. I pulled the TPS connector, and the the truck would run. Into the shop we went.

Pulled the throttle body, cleaned it, installed the new TPS, and adjusted it as per the manual. No change in how it ran.
Changed the Air Flow Meter, no change in how it ran, so it was returned.
Tested fuel pressure. Had 40 pounds (spec is 38-44) and it held as per manual's spec.
Tested the coil, found it bad, replaced it. No change in how it ran.
Replaced cap & rotor. No change.
Tested plug wires. Found most of them were over 200 ohms. Replaced the plug wires. Ran a little better.
Plugs were very wet. Cleaned them, and re-checked gap. Gap set at 0.031.

At this point, we made an interesting discovery. We started it with the intake tube disconnected. This shouldn't happen as the fuel pump circuit is tied to the air flow meter. Once started, the engine ran a little rough, but would idle. As it warmed up, we could slip the intake tube on and it would run even better. Almost like it should, except there was the occasional miss. Then if you pulled the air flow meter plug, it would die. Let it cool down and you could start it with the air flow meter disconnected. I assume this is due to the open loop/closed loop settings based on coolant temp. Once it was warm, I checked the fuel pump relay by manually actuating the door on the air valve. It clicks as I move it. We have constant fuel flow though regardless of door position.

At this point the stuff I've read here leads me to think that there may be a restriction in the exhaust (CAT) or the ECM is bad. Or could it be some other electrical gremlin?

Any ideas would be greatly appreciated. I can assure you that I will post back with the results as that kind of information has helped me in the past.

oldmandan

Curious about your beginning problem.Did it start out overheating and a blown headgasket at anytime?

307Yota

HG's were both good when I tore it down. it quit running because the bearings in the timing belt idler and tensioner pulleys came apart, causing the belt to come off.

307Yota

Messed with it again today. No real progress. Continues to start with the Air flow meter disconnected. Idles terribly. Won't stay running for very long.

Fuel pressure regulator tests ok.

Anyone have any ideas for me? I'm about to break down and either purchase or borrow an ECM and eliminate that as an issue.

307Yota

After much frustration and lack of input I finally visited the toyota dealer and spoke with the lead tech. He agreed with all that was done and laughed about some of the symptoms. Going to be a tough one to track down.....

He printed off a couple of wiring diagrams for me and wished me luck.

Started at the air flow sensor, tested it as per procedure in manual. Didn't pass. investigated further & discovered the pin-out we had was incorrect. found the right one, verified wire colors from new schematics, passed.

Tested ecm as per manual. Found two things. High resistance on the ground, and the coolant temp sensor readings were out of spec. Even though the sensor is new, it was bad. Verified by testing with a new one.

After we cleaned up grounds, the truck ran better.

Then we fixed an exhaust leak that was in front of the 02 sensor and the improvement was dramatic. the truck has never run this well.

thefishguy77

iTrader: (1)

Fantastic. I'm chasing codes as well. It's frustrating when a new motor runs great then starts to have issues.