rowdy235

Hi all, experiencing a little issue with my 78 hoping y'all can help. Mostly stock 78 pickup, 20r engine, 90% desmogged (only smog left is charcoal canister and EGR system). Sorry as this will be a particularly long post to get all the info in.

About three weeks ago I was coming home and the engine started to miss under load. Would run fine at idle, and up to about 1500-2k but if you pushed it higher it would act like it was dropping a cylinder (or two). I pulled over and found one of my plug wires had fallen and was resting on the header. Assuming that was the problem I rehung the wire and took off, but the problem persisted. I limped it home and once there began giving the engine a once-over, all to no avail. Finally out of desperation I re-timed it (just by ear) and the problem seemed to go away. I did go ahead and replace rotor, cap, and plug wires just to be safe as I had not replaced them since owning the truck.

Okay, so fast forward to yesterday. Went up in the woods to do some exploring, truck ran fine, good power, no issues, etc. Shut the truck off on the side of a slight uphill grade (no more than your average residential driveway), and went off for about 15 minutes. Came back and no start. Cranked over fine (more on that later) and in fact sounded like it was cranking over very quickly. I tried flooring it, pumping it, about everything you can do with the gas pedal and it never even popped.

Okay, here's where it gets weird. After rolling down to a flat area and trying unsuccessfully two more times to start it, I decided to have my wife crank while I checked for spark. I pulled the #1 plug wire off, stuck a screwdriver in the boot, and held the screwdriver against the valve cover. As she cranked there was spark, and then the engine started, like nothing ever happened (except it was running on 3, lol). I plugged the wire back in and we took off, all was fine.

We decided to head home and I was thinking about WTF the problem could be or could have been. And then, the unthinkable happened. After being stopped to put the gear away I (embarrassingly) stalled the engine when taking off. When I went to start it again, same as before, cranks good but won't fire. Luckily we were at the edge of a downhill so I got it rolling put it in 2nd and popped the clutch. We pry rolled 20-30' without anything happening and then the engine slowly came to life, but had a miss in it, especially when trying to go hard, just like the couple weeks prior. After another few hundred yards or so of driving/rolling it seemed to smooth out, and it was fine for the ride home.

Once I got home, I tried restarting immediately after shutting off and it fired right up. Did it two more times and no problems. Today I go out to start it and see if the problem is persisting and it cranked very slowly, like dead battery slow. When I let off the key, I hear the starter spin/disengage (short whining noise), hit the key again and cranked over quick and lit right off.

Prior to these issues, the only starting issues I had with the truck was occasional slow cranking (I always attributed to only driving once every couple weeks) and once in a while it was hard starting when warm, but would always start after turning over for a few seconds. I normally give it about half throttle when starting warm.

At this point I am torn between a fuel/carb or ignition problem. The symptoms to me tend to support the former but the fact that it started with one plug wire grounded and was missing when restarted the next time support the latter. For the fuel/carb, I'm thinking maladjusted float, carb leaking fuel into intake, or clogged fuel line/filter. For the ignition, I'm thinking weak coil, pickup going out, or maybe issue with advance (verified vac advance works sucking on hose). I have no idea if the slow cranking is related or not, but it seems to be something intermittent, as yesterday I probably cranked the engine for 2-3 minutes total (not at once obviously) with no hesitation, and this morning it wouldn't even crank hardly.

Starter is about a year old, plugs/wires/cap/rotor have recently been replaced, fuel lines and filter were redone about a year and a half ago. Carb has never been apart since it seemed to run good. Once running the engine always seems to do fine, idles at 900 smooth, good power, acceleration, etc.

Any ideas you guys have would be much appreciated.

WolfMann

Have you checked if the egr is clogged? You said it was still attached right? Is your charging system alright, 14v at the battery? How did the spark plugs look? Also what carb are you running, Is this a Weber or Aisin, has it been cleaned in awhile? Also wondering about the fuel filter, have you replaced it recently?

rowdy235

Haven't checked the EGR, its still hooked up but no idea if its working. I'll check that this weekend.
Volt gauge shows 14 or so volts while running, charging system seems fine. At times engine cranks over great, other times acts like battery is dead. Weird.
Didn't pull the plugs when all this was going on but they have looked fine in the past, I'll pull them (or at least one) this weekend and check
Stock Aisin Carb, never cleaned as far as I know. Just seemed to work fine so didn't see the reason to. Might be time too though.
Fuel filter was replaced about 2 years back, truck has maybe 1000 miles on it since. Looked at it the other day and looked fine, but will blow some air through it to be sure.
I also checked the sight glass on carb, weird shape, but if you picture it like )=(, the fuel was just above the bottom edge of the middle portion, which seems pretty close to normal to me.

Been reading around about potential of failing coil. Gonna run a test on the coil this weekend both cold and warm and see if it may be on the way out.

highonpottery

iTrader: (1)

On the battery comment - have you checked grounds?

Did you do the ignition conversion on this truck? I know my 75 came with points originally and the PO converted it to distributor with used parts off a donor. If you didn't do yours, the PO could have done the same and installed used parts, which could be a possible culprit.

rickc5

Same things I was thinking. A ground could be loose, which would be intermittent. Yes, I would also verify that all was OK & as it should be inside the distributor. Also check all electrical connections for the distributor. All this is free, just time consuming.

rowdy235

Good ideas guys. I'll check all the grounds this weekend, think I'm also going to clean up all the connectors on the distrubtor/ignitor/coil, hard to tell what a little corrosion could do in there.

I believe 78 was the first year of factory electronic ignition. Everything looked good under the dist cap last time, but I'll check again just to be sure this weekend.

rowdy235

Sorry guys got busy last weekend so didn't get a chance to work on the truck but I did get a chance today.

First thing I did was to clean up all the connections and inspect the grounds. All grounds looked good but my Negative battery cable is in rough shape (more on that later)

I fired up the truck and let it warm up, put my timing light on it and was right at 8° BTDC with the advance disconnected (guess my timing by ear works out after all, lol) I checked over for vacuum leaks and wasn't able to find any. I went ahead and went back to square one so to speak with the carburetor. I set all screws to factory settings and tuned from there. I believe my idle mixture may have been too rich- which could have contributed to the hard warm start (had been idling 5-10 minutes before shutting off each time)

Once I was satisfied with how the truck was running (better than ever IMO). I did a series of shutting off and restarting, trying to duplicate the issue. I waited anywhere from 5 minutes to an hour and each time the truck started within 2-3 revolutions. So I am hoping my issue may have just been flooding due to the rich idle mixture and idling for extended time prior to shutoff.

I did run the tests on my coil and it appears to have failed. Per my service manual there is supposed to be between 1.3 and 1.7 ohms between the + and - terminals, I got about 30 ohms. The same manual calls for between 6500 and 10500 ohms between the + and high-tension post, and I saw about 11,500. Whats odd is that it seems to run fine, but I guess this may be indicative of a coil on the way out? May replace it for peace of mind as its only about $13.

Also, slow cranking continues to be an issue. It seems to be rather intermittent. For instance, I had started the engine 4-5 times just fine and turned the key and won't even turn over. Hit the key again and spins over fine. My positive battery lead appears to have been recently replaced and in good shape, but the negative not so much. First order of business will be to replace that. Does anybody know where the - cable grounds to the engine? I keep seeing a 10" cable called for and mine is much longer- it runs down the fender and mounts ahead of the motor mount near the bottom of the block. Not sure on the length- but longer than 10" for sure. But in theory I should be able to ground anywhere (within reason, obviously) on the block, right? If still no improvement, I will probably start looking towards a battery or starter issue. Hopefully not the latter as the starter is only a few months out of warranty, although it would be my luck.

Thanks guys for the help and hope I can get the remaining issues resolved.

rowdy235

Looks like the reason my negative cable is different is because my engine has A/C and an Air pump, my buddies 20R has the cable attached to where my A/C compressor is mounted. However, I am a bit perplexed as to how toyota ran the ground. Basically the ground wire runs from the battery to the frame and then to the block. I cannot tell if there is actually a separate wire that jumpers the wire to the block or if its one wire.
(Battery -----------Bolt on Frame--Bolt on Engine if that makes it any clearer). The second link (between the frame and engine) is maybe 6".

I'm going to replace both battery cables just to be safe and the coil as well. What does everybody think of 2 ga vs 4 ga? I can get either, but seems like 2 ga may be a bit overkill for a 20r IMO. Thoughts?

Also, I think for the negative I am going to see if I can find a short cable with lugs on both ends and run my main ground wire from the battery to the engine, and then use the jumper wire to the frame. I don't understand why they would have run a huge wire down to the frame- nothing grounds to the frame itself I can think of except the fuel pump and rear lights. Everything else is grounded to the body or engine. Maybe because it was a motorhome? I am sure the starter is by far the largest draw on the battery so I think the main ground should go to the block. Thoughts?

EDIT: I am considering replacing my engine to body ground with a new 10 gauge wire. Does anybody see an issue with running a 10 gauge wire between the engine and frame as well? Seems to be should be fine seeing its a short distance.

L5wolvesf

I know the earlier model pickups are wired differently than the 84/5 and up but, the wiring and switches are still over 3 decades old. The first thing I thought was your intermittent start/no start issue seems a lot like mine and others here. Many of us had new starters and it didn't matter. The problem is full cranking power/amps is sent through the ignition switch. Many of their problems have been resolved by installing a starter relay - a very simple job for the later pickups.

But, like I said I don't know for sure if your truck would have the stock switch wired similarly to an 84 on.

I suggest you search starter relay on the 84/85 or 86 on forums. Look for posts by RAD4runner - he is the electrical guru here.

rowdy235

Interesting, of all the things I never really took the ignition switch and related wiring into consideration. Upon reading some of the later models took 12 amps to trigger the starter solenoid. That's truly shocking and honestly nothing more than a shoddy design IMO. Looks like they changed the starters in 84 so not sure if the later starters were different than the earlier ones. I've had several first gens and "pre-gens" and never had one with a starter relay, never seen an ignition switch fail either, and my 82 had 300k+ on it, but that's not to say it can't happen.

The earlier models are wired very simply, the ignition switch just feeds power to the starter solenoid when turned to start. It looks like Toyota added a factory relay in order to address the high amperage around 1984, but most posts I've found indicate the factory relay was essentially useless and most people replace it.

It would be simple enough to wire a relay in to an earlier model, which I may keep in mind if I continue having issues. I also have a push-button jumper wire made up I may try utilizing to see if there is any difference- as this would bypass the ignition switch.

I got all the new battery cables today on sale. Pry going to put in this weekend and will see what happens.

Thanks all for the help so far!

95yoda

My 82 only had a ground from neg post to inner fender about 8in of wire. Then it had a motor mount to frame ground also going in 2 directions, neither to the block.
I ran one not only to fender but also to engine block. It performs better now.

rowdy235

Replaced the battery cables with new 4 gauge cables. The old ones were in pretty rough shape. The ground actually had three lugs on it. To the fender, frame, and block in that order. The new cable runs straight to the block and has a jumper wire to the frame from the engine block, and the secondary lead I grounded to the fender.

Also replaced the coil which was pretty straight forward. The old coil sloshes when shaken which is a sure sign its bad.

Seems to start very good now. When warm, it doesn't even turn over a whole revolution before it fires. I drove around all weekend running errands and what not and never missed a beat. I'm chalking up the hard starting to a combination of weak coil and mis-adjusted carburetor causing flooding after idling. The slow cranking I believe was related to the battery cables but I also am going to have my battery tested in the future just to make sure its up to snuff.

Thanks all for the help!

95yoda

Glad it's sorted out. Yeah these trucks tend to fire in a millisecond. My last 82 did too.