Thook, I got the speed sensor off without too much blood. Three terminals showing. Looked at each of the 3 possible pairs. They were all in the range of 20 - 40 kOhms. Strange thing is that non of them vary as I rotate (by hand) the gear. Took the cap off and see that this must be a hall effect sensor or similar. Is this correct? I searched yotatech for specs as well as the FSM, but find nothing yet.

On a different note, I started to remove the O2 sensor but the nuts are so rusted that I can't get them with a box end wrench. Do the studs back out? Or will I have to drill them out and tap it if they break off?

 

On my '91, one of the studs backed out of the pipe so I assume your's could as well, but they could break too. Soak 'em with wd or similar for a while and see if that helps.

On my '88, it threw a 41 and 42 and the same time and replacing the TPS took care of the problem. Well at least for the last 1500 miles or so.

Also, as thook mentioned, the AFM could be going since the fuel pump should only run for a few moments when the key is turned on then shut off if the engine isn't started. There's a switch in the meter that energizes the pump if air starts flowing through it.
Now that I think about it, maybe the meter is stuck open?

 

Got em soaking in PB Blaster right now.

When you threw the 41/42 codes, what were your symptoms?

Just got the VAF back together after cleaning it and measuring the contacts. It checks out OK according to the FSM specs. AFter putting it back on, I started the engine and saw no difference. Like it is running on two cylinders. Begining to think the injector(s) are bad.

 

it also threw a 51. it was rough running, misfiring at whatever engine speed it wanted to, occasionally dying at stops, mileage when down the crapper. after replacing the tps all three codes were gone and it was fine for a few days then threw a 14 which was fixed by replacing the ignitor and coil. coincidence? don't know.

Anyways, maybe try unplugging the wires from the cold start injector- it's on top of the intake near the middle. It could be staying open too long and spraying fuel into the engine causing it to run bad. If it's not closing when it's supposed to, it could be the cold start injector time switch.

 

Thanks. I pulled the cold start injector power yesterday and it made no difference.

Still can't figure out why the fuel pump remains on with the key on. The fuel rail is noisy right around injector #4 and the fuel pressure regulator. Kinda sounds like the #4 injector is staying open, bleeding the fuel pressure and subsequently keeping the fuel pump running?

 

That's why you try to find a good, used one first!.... Even before that, you should test yours.

Ah piss! Was trying to go by memory....it was a while back. I may have unintentionally misdirected you on the spd sensor test the way I explained it and what I did. Very sorry about that.....very sorry. I'm going to say yours is good, though. The main crux is that it shows a steady positive reading....that the circuit is intact. The important thing.

Before you break anything, I seriously suggest spraying PB Blaster on the nuts (as you've done) and tapping, tapping, tapping, and tapping to work it in to the threads. Spray the penetrate on there and continue tapping on them with a deep well socket and hammer until they break free easily. You do not want to break the studs. Even if they do come out with the nuts, that's better than having to drill and rethread that cast metal. Royal pain in the butt!!! Aside from that, I'm not real familiar with testing a heated O2 sensor. The one on my '86 is a single wire unit and is simple enough to test on the vehicle without having to remove it. So, I'd have to do some research before I can be of any help there.

Okay.....I did some reading a while back on a continually running fuel pump and I know it's related to the ECM, somehow. But, before I try to go by memory again, let me dig up the info I'd read at the time I was having that problem with my '92. If it is the ECM, it would explain everything. More later, though.

 

Thook, man as much help as you are to me and everyone else, no sweat. Can't expect you to be my FSM. Heh, even the FSM that I downloaded is riddled with typos and other errors. Sometimes I even doubt the numbers in the chart owing to the number of mistakes in printing/spelling

I found a local chop shop that can get me an ECM for ~$150. Only guarantee they give is that they will replace it with another used one. I am going to order this knowing it will take a week or so to get here. If I find my problem in the mean time, I will have not lost too much money. Better than blindly replacing so many sensors.

 

Last night I printed out the FSM 2-page troubleshooting chart. I circled every symptom I had and then added up the number of circles for each column, looking at the columns with the greater number of circles. Given my symptoms, the engine coolant sensor, VAF, fuel pressure regulator, injectors and cold start system come in at 5 to 6 circles. I can mark off the VAF and cold start system as I have checked each of these per FSM specs. Going to spend the day with my daughter and then look over the fuel pressure system on Sunday. Attack the injectors last.

 

Actually, I have found contradictions/mistakes in the FSM's, myself. So, I know what you're saying. Scary.....isn't it?!

$150 is a lot for a used ECM, in my book. I paid $50 for the '92. But, that was from a fellow on YT and there was no guaranteed replacement. And, I realize sometimes you have to have one pronto and that kinda balances the cost.

The constant running fuel pump is a circuit specific issue and has nothing do with injectors, fuel pressure, ECT sensor, or cold start system. So, since you've already ruled out the VAF meter and cold start, that narrows it down tremendously; the ECM, and maybe....on second thought....even the fuel pump relay....though I don't recall reading about that being a possibility. Anyway, those are not "hard" to inspect.....just a bit tedious. Fortunately, the FSM does cover that well enough and that's where I'd attack next.

Have fun with your daughter, hickman.....and, good luck diagnosticating.

 

If you're gonna do the ECU, give these guys a call: https://www.yotatech.com/forums/f123...l#post50716916
I was in there a week and a half ago and they had ECU's for 79 bucks and will ship it to you.

 

Thanks, I will be giving them a call tomorrow.

 

Aaron, if you wouldn't mind, would you please recap on what you've ruled out thus far? And, have the codes come back at all?

I'm going to a bit of research tomorrow and what I can come up with for you. I like the learning in it, and I found some neat articles, anway. So....

 

Sure. Here goes....

Symptoms:

1. Stopped to grab a hamburger. Started truck (22re) and noticed the idle would drop between shifts. Within 1/2 mile, the engine began to "stumble" and run very rough. Pulled over in parking lot and pushed in cluth/neutral. Engine acted like it wanted to stall, but never completely shut off.

2. Drove it home next morning with same symptoms. Noticed that at higher RPMS (2200 - 3000), the hesitation and power got much better. However if I let off gas to coast or slow down, I felt the rough idle.

3. Engine progressively got worse and has lost significant power. Second gear barely has enought power to keep truck moving forward. Engine never dies out completely, however.

4. Never got a CEL light.


Troubleshooting steps:

1. Pulled diag codes, receiving a 41 and 42 (TPS and speed sensor). Pulled and cleaned TPS and speed sensor. OK according to FSM. Installed and set TPS to factory default. Measured perfect.

2. Cleared codes (pulled neg. cable) and fired engine back up. No CEL or diag codes. Engine runs, but same symptoms.

2.5 Checked (starting fluid) for vacuum leaks. None detected.

3. Checked timing with gun. OK.

4. Checked cold start injector circuit. OK

5. Checked and cleaned VAF. OK

6. Checked O2 sensor with ohm meter. OK

7. Checked ECT sensor. OK

8. Checked EGR and temp. sensor. OK

9. Shorted TE1 and T1 to look for additional codes. Nothing additional.

10. Removed plugs, all 4 are fouled and wet.

11. Compression test, all 4 are ~150 psi.

12. Noticed that fuel pump runs continuously when TE1 and T1 are shorted for diag mode. Also noticed that fuel regulator and/or #4 injector (same location) are noisy. Almost like fuel/air is constantly flowing. No leaks.

13. Pulled throttle body and plenum off. Removed injectors and tested each. OK. However one injector pintle cap was broken and missing. Others had cracked caps as well.

14. Then end.

 

Thanks, Aaron.

Okay....I still say ECM because jumping the diagnostic terminals should not cause the fuel pump to run continuously. That's a malfunction, I know, but I don't know why it would be doing that. All I can figure is some circuit is crossing where it shouldn't be.

Have you visually inspected the ECM, by chance?

 

Yep. I even removed power and all ribbon cables/plugs for 20 min. Just printed out the FSM for the ECM troubleshooting. Wow, what a task to troubleshoot. Got my diagnosticator tool on my belt loop and am heading home.

 

Ummmm.....I said I'd do some reading....and, I did! Only it wasn't really about the ECM "specifically"...lol! Anyway, good info and might help a bit.

http://www.autoshop101.com/

This is what I'll be studying next. It is specifically about the ECM. I do believe understanding how things work is the key to understanding what's going wrong.

http://www.autoshop101.com/

BTW, you guys should really make your acquaintence with this site. The more I read it, the more I realize there's SOOOO much about EFI's I simply do not know. Blows my mind! Funny thing is, once you read and understand, it's not really that complicated. Sorta primitive, actually. "Ungh....me turn key. Me drive car. Where Taco Bell?"

 

yep, is weird about EFI... there's so many sensors and wires and... well... when things don't work it's too complicated, but when you really sit down and think about it, each sensor does a specific thing. And when you get a trouble code or whatever, it points you in a certain direction... and when two or more sensors collide, the specific circumstances around the problem point to the solution.
It works hot or cold... idle, transition from idle to acceleration, constant throttle, O2... hmmm...

Call me up with a problem about a pontiac 400 stumbling off idle and I'll give you 10 different ways to check 5 things.

 

Ironically I had settled on the same site late last night after searching through my Favorites. Fell asleep with laptop in hand. I went straight the the sensor section under OBD and then pick-and-choose through OBDII. Their explaination of the ECU as related to the feedback sensors is much clearer than the FSM.

Matthew, I could not agree more in that knowledge is power and that once you read a little, the light bulb usually clinks on allowing you to see the through the glass rather than just your dumbfounded reflection Sometime, however, it takes a little assistance from others to get your footing while jumping over the learning curve hurdle. Thanks for you continued help!

UPS tracking shows my shims coming in today for my 3.0 rebuild. Maybe I will be able to put the bike back in storage by week's end and have at least one running vehicle. Rain is in the forecast and I hate to waste money on drycleaning shirts and pants.

 

Righto, Abe. Codes can be very helpful. Track down the circuit and eventually you'll find the problem. A little different when it comes to mechanicals, though. I guess that's why auto engineers developed electronic sensors and whatnot, eh?

Autoshop101 is a technical training website.The factory repair manuals are written under the assumption that the technician reading it has already had this training to understand and use it. I kinda wish I'd known about it sooner than the few months ago when I'd found it. Since then, I've been trying to tell everyone I can about it. It's frustrating grabbing at straws with the FSM alone. The funny thing is 4crawler's had the link posted on his website.....for several years! Bah!

Nice analogy, Aaron. Why don't we just break the damn glass? I've got a wrench I bet'll go right through...lol!

 

Here it is...
http://www.autoshop101.com/forms/h42.pdf

After you've read it, you'll see what I mean about the circuits and possibly why the fuel pump constantly runs.

The other thought I had is that to check for codes with the TE1-E1 terminals, the key must be on. So, the FP running probably has nothing to do with the diagnostic terminals at all....rather it's the fact you have the key on, but still boils down to the ECU as it controls the ON/OFF of the fuel pump circuit.

You can rule out the VAM altogether by this, incidentally. The fuel pump switch in the VAM is not active until the motor is running.