need help with OBD1

I have a 1992 chevy 1500 pickup. The symptoms are that it seems to go in and out of "safe mode" or "limp home mode" at irregular intervals. The truck runs fine but very suddenly will act like its not getting enough fire to the plugs and an odor of running veyr rich with a loss of power. It run run like this for several miles and then suddenly begin running correctly again.

It will do this off and on untill it gradually gets to the point where it stays in "limp home" type mode.

The cat has been replaced, the coil has been replaced and the wires with no effect. A buddy says that also when in this "mode" it appears that half the throttle body is not getting fuel to it????

We replaced the OBD1 computer and the truck ran fine for over 1500 miles and then started acting as before. Replaced that OBD1 computer with another one and it again ran fine for 400 miles and now is intermitely acting up again as before.

Any thoughts would be appreciated.

Reply to
contender
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Kinda sounds like something is fu@king with your ECM.

I'd start by looking for a bad ground and then an over-voltage situation.

If you have one left over, open it up and see if something's fried...

Reply to
Hachiroku $B%O%A%m%/(B

Plugs look like they are in good shape? Fuel pressure is good?

Checked all the wiring including the wiring to the O2 sensor? If the O2 sensor drops out, the computer will go into limp home mode. Clean the connectors, pump a little dielectric grease in there. Do the same for the engine sensors.

That sure sounds like the problem isn't the computer, but it might be the connector going into the computer which you reseated when you replaced the computer.

Does the computer log any error codes? You really need to be looking at the codes. 33, 34, 13 maybe?

--scott

Reply to
Scott Dorsey

He can just remove and reinstall the new computer. If it's fine again for several hundred miles, then it's probably a loose fitting terminal in one of the connectors at the ECM.

Reply to
Bill Vanek

In order to help we need to know what codes the ecm has stored... (I am guessing a 43) You can pull codes with a paper clip, directions are all over google. HTH and let us know, Ben

Reply to
ben91932

Can't say the same may happen with yours but, I have recently been having a similar problem with a Bronco and an F150. Both have been mysteriously losing a small amout of coolant. It was no problem adding a bit of coolant every month or so but, eventually both started to have sporadic misfires and the appearance of running rich. Both got the usual wires, cap, rotor, plugs filters, etc. Throughout the process, the O2 sensors, ignition pickup, control modules and coils have been replaced with no effect and no fault codes. Whatever, both returned to the erratic misfires, rich mix, poor fuel milege and low power. After this started again, I pulled the O2 sensors again and, again, found them fouled with a brownish colored residue instead of the black I saw before. After a lot of head scratching, I decided to run a dye test on the cooling system and found the intake manifiled leaking on #8 cylinder on both. After replacing the intake gaskets, both have remained glitch-free. It also cost me more O2 sensors. It may have been possible to save the O2 sensors by burning off the residue with a propane torch. I have seen some racers use this at the track when they fuel foul them and are working on a budget.

If you are losing any coolant at all, you should track down the cause and fix that. IIRC, some of the 90's Chevies had some intake gasket problems as well. It appears O2 sensors do not like etheleneglycol very much. Now, I'll get on the blown explorer head gasket job.

Lugnut

Reply to
lugnut

Yes, precisely!

--scott

Reply to
Scott Dorsey
1500 miles > > and then started acting as before. Replaced that OBD1 computer with > > another one and it again ran fine for 400 miles and now is intermitely > > acting up again as before. > > > > Any thoughts would be appreciated. > > > Hachiroku $B%O%A%m%/(B wrote: > > > > Kinda sounds like something is fu@king with your ECM. > > I'd start by looking for a bad ground and then an over-voltage situation. > > If you have one left over, open it up and see if something's fried...

we had the orginal obd1 and part of the inside did appear to be fried as in it got too hot. We do not have the replacements as they were returned under warranty.

just orginally thought it was old age/wore out. what causes an obd1 to "fry"? I thought there were fuses to protect it from such.

The unusual thing is the OBD1's as in the orginial and the replacements are not showing any codes on a friends reader which can read obd1 systems.

Reply to
contender

Yes, there are fuses, but we're talking electronics here. It always tries to seek out a ground, and if the usual path to ground is kaput it will try to find another way. Example: I had an 80 Corolla I bought brand new. In

1982 (and ~75,000 miles) I stopped to get a cuppa before my 60 mile trip to work, and it was misting so I had the wipers on delay (delay! A Toyota with delay!!! (it was a big thing then...))

I puled up nose-in to the GREAT BIG CEMENT WALL, turned the ignition off, set the parking brake like I always do, took my foot off the clutch...and the car lurched forward!

Now, i had to get up pretty early to get to work on time, and thought, "DUMBASS! SHUT THE CAR OFF FIRST!!!!" only to look down and see the keys dangling from my hand. Then I noticed the charge light and Check Engine light were on, and the volt meter was measuring about 6 volts! I turned the ignition on, without starting, and turned it off. Lights and meter went otu, up to 12 V and back to on and 6V...

Then I shut off the wipers...everything went off...

When I got to work, I called the local Toy Store, and a tech told me one of the g__ks in the factory overtightened the fuse box ground. I replaced it with a screw and a washer, and no problems.

So, what happened when the car lurched forward ws, the WHOLE ignition system was groundng through the windshield wipers!!!

No blown fuses, no other damage. That's why loose or non-conducting grounds are such a BITCH to troubleshoot! It will find another path to ground, through whatever it can.

So, I would be looking at the grounds in that area of the vehicle; get a wiring diagram and trace out the grounds for the ECU. I think that's your problem.

Good luck!

Er, BTW, it could be a ground to another system on the vehicle. I really HATE automotive electrical systems...and check out the harness for worn insulation, too...

Reply to
Hachiroku $B%O%A%m%/(B

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