Speedmonster185

Hey guys, I'm new here. I've been over at LS1Tech for a while since I have a 2000 WS6, but I just recently got a '93 Z28 for a daily driver. When I got it there were no engine lights or anything, but now slowly I started getting one more and more until now it comes on every time I run the car after a couple minutes. I checked the code and it is DTC 26. I've been reading on Shoebox's site and Fastbird93's, and I've tried a few things so far.

I know it is definitely not the relay for the AIR pump (relay E in the manual), and I know it's not the fuse that has the EVAP, AIR and EGR on it (#6 in the manual). I checked all of those last night.

I do have a question though. Is it possible that my EVAP Purge Solenoid is bad? I heard from somewhere there should be an audible ticking from it while the car is running, but I can't hear a thing coming from mine. I can get right down by it and don't hear anything. I touched it too and don't feel anything at all.

Thanks guys

Speedmonster185

Anybody know? I bought a new EVAP solenoid and I can just go put it in if you think that might solve the problem, but I don't want to if there's no chance that could be it. What do you think?

n2ceptor

Is this a stock engine??????? Any mods??????? Anything disabled??????

Speedmonster185

Nope. Sorry I didn't mention that. It's 100% completely stock down to the paper filter. Nothing at all disabled or anything.

I tried the new solenoid and it didn't help any. So that wasn't it... Any ideas for what to try next?

Also.... as of last night I have another light too... this one is DTC 34. I don't really know what to do about that one yet except replacing the MAP maybe? I haven't looked into it much yet.

Injuneer

Did you verify there is a good fuse in the AIR pump circuit? The code is not just for the relay. My Chiltons wiring diagram for the 93 shows the AIR pump is on fuse #7. It shows #6 for the other solenoids - could be wrong I guess.

The EGR and EVAP solenoids should react the same way. Supply a ground to the non-brown wire, and it should open (KOEO). You could also check the relays to see if they are presenting the correct load to the electrical circuit, since that is all the PCM can check. I believe the solenoids are about 12-15ohms across the coils???

The DTC 26 code also applies to the driver module for all the loads on it, so that could be faulty.

DTC 34 = MAP sensor signal (voltage) low/vacuum high. Check the harness connector. They dry out, crumble and start to give erratic voltage readings.

Speedmonster185

Oh, I completely forgot that one . Yeah thats what the diagram I was using says too, but my printer was running out of ink so I couldn't read that one and I forgot it. haha. So thanks .

Ok, so for the MAP sensor harness connector (I'm assuming you mean the plastic plug? I'm new to electrical stuff in cars... sorry), what should I do about that? First off how do I make sure that's what it is, and then what do I need to do if it is? Just replace it?

Thanks for your help .

Speedmonster185

Ok, well here are some new developments as of just a minute ago.

I went out and pulled fuse #7 like you said, and it was blown. So I was happy. haha. Then I replaced it with the fog light fuse (both 20 amps) and tried running it with that. Here is what I noticed while I was running it, and what happened.

The car once again threw the DTC 34 code immediately when I turned it on, but I lert it run for a while, and tried revving it a bit after a while to see if the DTC 26 code would come on. While I was revving it I noticed that the car won't go above 3000rpm now if you slowly rev it. IF you stomp on it it will go above that, but I think thats only because the engine's momentum carries it above there. Other than that I can slowly put my foot all the way down and it will hover around 3000 surging up and down a couple hundred rpms. Would that be related to the MAP?

After I got done I checked for codes again and there was a DTC 26 again, and still the 34. So I got out and checked the fuse, and it was blown again. Does that mean there is something wrong with my air pump and it needs to be replaced?

Injuneer

Yes, the AIR pumps sieze up due to rust. Simply unplug the AIR pump harness connector, and then replace your fuse. The pump will not run, but the ECM will also not set the code. The pump only runs for a couple minutes at startup to help the cat heat up faster.

The MAP sensor gets a +5V reference signal from the PCM. Use a volt meter to measure between the black and gray wires to make sure you have +5V with the key on/engine off. Now probe with the volt meter between the light green wire and the black wire. With the key on, engine off, the system should be close to +5V, but not quite. How much you will below 5V depends on the altitude where you are.... at sea level you will see about 4.9V, at 5000-ft elevation you will see about 4.0V. Jiggle the harness connector while watching the volt meter. The voltage should not jump around. If it does, you have a faulty connector. Then start the car and let it idle. Voltage between the light green and black wires should be about 1.2-1.5V. Again, jiggle the connector. If the voltage falls below about 0.4V it will set DTC 34.

Speedmonster185

Ok thanks. I can do that stuff. I'll have to go get a couple new fuses since I have two blown ones now... and I'll have to get a volt meter since I don't have one and I think my dad threw away his old one... lol.

Once I get that stuff I'll let you know how it goes and if anything else comes up.

Thanks for the help.

Speedmonster185

Ok, so here what's going on right now. I just did what you said with the AIR pump. I replaced the fuses and unplugged the pump, and now the DTC 26 doesn't come on anymore. But the weird thing is, the 34 isn't coming on anymore. I left the car running for like 20 minutes and wiggled around the wires and the connector and stuff, and nothing. No code. Then I drove it a couple miles around the block (out in the country) and stepped on it through 2nd a couple times, and still no code. No nothing. It feels like it's running better than before at idle too. Much smoother. Could I possibly have done something before while messing with all the evap plugs and tubes and stuff to set off that code? I don't understand why it would just go away.

Speedmonster185

ttt...

Injuneer

If the MAP connector was loose, you may have reseated it while jiggling the wires. I'd still consider replacing the pigtail, since there may still be damage to the connector. They are known for crumbling with age.

Speedmonster185

Ok. Would I be able to see that if it was getting bad enough? As far as I could see it still looked solid to me, but I don't know if I could even see the area that would cause the problem.

Injuneer

The pigtail an item that will cost you a couple bucks in an auto parts store.

Speedmonster185

Ok, well I just started it up for about 10 seconds today and the light was already on . lol. So all that driving and stuff didn't do it, but sitting there did. Weird. Guess I'll be checking out those voltages in the next couple days... :P