Cerridius

Hey everyone, so I've been trying to figure out whats up with my car lately. Seems to run smooth and better when its cold, and i guess fine at WOT. But when its warmed normal driving is not so smooth, and WOT seems fine too.. i guess.

When its warm if i take off slowly it will kind of stumble for a half second and continue on and if i give it more gas I can kind of hear like a steady pop in the exhaust, almost like a miss. It doesn't have that pop noise when cold and it doesn't stumble either cold.

New plugs and stock wires (is it possible to put to much dielectric grease on the plug wire ends?)
New MSD ICM spaced off the head with plenty of grease in between.
Cleaned the MAF.


Now the big thing that popped up is a SES light randomly comes on and then will go off about 10 seconds later everyonce in a while. I pulled this Code and its Code 43. (94 Z28 OBD1)

I've read up on this code which appears to deal with the knock sensor stuff. (wiring KS KM, i guess)

I also read some diagnosing, and did a tad bit. I guess im kind of retarded with an OHM meter because I could not figure out how to get the resistance of the knock sensor. This sensor is fairly new though (maybe 5k miles) but i went ahead and replaced it anyway (torqued 14-15ftlbs) I read that the wire going to the sensor is suppose to have 5v with the key on, the most I could get out of it was 4.78v?

I haven't tested the D22(?) pin yet because Im not sure where to find it (on PCM i assume)

I hooked up my scanner also to check out some stuff, idk if it matters but at idle i have about 23-27* of timing and at WOT its 32* with 4-5* of Knock retard, at normal driving I was still getting knock retard ranging from 0-7* of retard. Also largest knock count was 22,000+ (dont know if that matters)


I also read that sometimes people have problems with the LT4 knock module and saying how it actually caused more knock retard?? I think my PCM was desensitized when it was tuned so i may try swapping in my GFs LT1 knock module and scanning again later

Car seems like its down on power some. 8.34 at 83mph 1.89 60ft was my best time (old madz28 tune) I have gone to the track with my new Madz28 update (I had him lean the car out some from the previous 11.8:1 AF and adjust the 2-3 shift point.) but wasn't able to get a good run because I was spinning on my tires which i normally don't. (which may be a good sign)

Thank you



94 Z28 LT1 OBD1 Madz28 tune
Ported Heads/Intake
CC503 cam
1.6rockers
K&N CAI, Vortec elbow
36lb injectors
Longtube headers
ORY pipe flowmaster catback (borla muff in place)
and so on.

AdsoYo

I think as long as you have metal on metal you're fine.

Electrical problems are the worst. Have you checked the knock sensor wire to make sure it's not burned or too close to the exhaust? Maybe unplug the harness from the PCM and check for continuity, too?

I tried to link shoebox's PCM pinouts but the link on his site is broken

Cerridius

I havent traces the knock sensor wire yet, I plan to do that later. And no I'm not sure what pin to test on the back of the computer. I know it's d22, but idk what d22 is. I've been reading more and it seems like everything causes these problems.

Im not sure but with my IAC my vortec elbow has a threaded hole. My IAC was a push in and bigger so I grinded the threads off and shoved it in the vortec elbow. Does it need to be completely flush? I'd say there is about an 1/8 of an inch between the base and the elbow.

I read that a MAP sensor causes similar problems. Not nessacerily tue sensor itself, but the plug. Well my plug little clip part is broken off (became brittle over time) and its pushed in... But I wonder if the clip is needed to get full contact. Anyway I guess I'll replace that pigtail today and I have another map sensor laying around from a spare intake manifold.

I'll also try going back to an LT1 knock module later.

Cerridius

I also forgot to mention that it's difficult to accelerate at low speeds in a high gear. (50mph in 4th gear. A4). The whole car like shakes as bucks and barely goes until I downshift it.

And I forgot to say that ive been getting some intake backfires. Sometimes when I floor it. 1 pop and then it goes. If I give it maybe a half throttle blip at lower rpm sometimes it will intake backfire.

Injuneer

When you measured the voltage on the single wire to the knock sensor, key on - what did you use as a ground? Use the engine, and make sure you clean off any crud where you touch the probe.

The knock sensor has a single pin, for the single wire harness connector. With the harness off the pin, put the + lead on the single pin on the knock sensor, and the other - lead to a clean engine ground. Read the ohms - should be in the range of 3500-5500 ohms.

Plug the harness connector back in. With a straight pin to penetrate the wire insulation, measure the voltage from the single wire to the clean engine ground. Should be in the range of 1.5 - 2.5volts. While you are doing this, jiggle the wire to see if you have an intermittent connection.

In a 94, the code sets when the voltage exceeds 4.1 volts, or falls under 0.78 volts for 5 seconds.

When the code sets, the PCM retards the ignition timing almost constantly, based on engine operating conditions. When you lug the engine at low speeds in high gear (never a good idea) you're going to be exposing the engine to conditions that are likely to cause knock. If the sensor is working, the PCM will pull timing until the knock disappears.. If the sensor is not working (code set), the PCM will pull out a lot of timing based on the engine operating conditions - low rpm, high MAP, throw in hot temps for coolant and IAT and you'll see a lot of retard. When you pull timing, power falls off.

Shoebox has the connector pinouts for the PCM, and pin D22 is on the blue connector:

4th Gen LT1 F-body Tech Articles

Cerridius

I measured the connector plug using a body ground and then the starter bolts. I must of broke my ohm meter because I can't get it to read resistance.

I'll test the wire like you said by stabbing it and wiggling. I'll fix my map pigtail to.

I'll post up any results.

Cerridius

Ok I went out and did some testing.

Connector with key on 4.7v
Knock sensor was 3.9-4.1 (in 20k? on the ohm... only way i could get it to read)
Stabbed the wire while plugged in and it was 2.38 while connected to the KS
Stabbed up top with the wire disconnected from the KS and right by the blue connecter 4.7v


And then I went as far as unplugging the blue harness plug and tested the Pin on the PCM, (D22) and the pin measured.. 4.7v..

Sooo could that be my problem? If so Im assuming the actual knock module (LT4) itself is going bad???

Injuneer

The knock module filters the signal from the knock sensor. It's conceivable it could somehow affect the voltage supply. But there is a separate trouble code for the knock module.

I don't think having a slightly lower than expected voltage is going to cause your problems. The knock sensor appears to be OK. All your other readings look fine.

I'm a bit confused.... you indicated you can't get the ohm meter to work, but then you appear to be getting 3,900 - 4,100 ohms.

Are you testing the voltage with the engine running? If not, you may have low battery voltage with the key on and the engine not running. Or you may have weak grounds on the PCM. or poor engine grounds. Did you use teflon tape on the threads of the knock sensor?

Check the voltage between the gray and black wires to the TPS, connector off the sensor. Do the same with the black and gray wires to the MAP sensor.

Cerridius

Sorry for the confusion. I bought a new multimeter because I think I fried my other one which is why I couldn't get a reading.

No I didn't put anything on the knock sensor. Just installed it with the stuff already on it.

No I did all the testing with the engine off, I didn't want to start the car with the whole blue plug unplugged on the PCM. But I suppose I can test the D22 wire next to the PCM by stabbing it with the engine on.

Ok I'll test the TPS and MAP. What should they be? 5v also?

Injuneer

Put the blue connector back on, then start the engine. Retest the voltage at the connector at the end of the knock sensor wire. You've already established that you get the same voltage on both ends of the wire.

Yes, TPS and MAP also should be at 5.0V. Pulling the TPS or MAP connectors off with the engine running will set codes, so try measuring those with key on/engine off, to see if you get the same reading as you get with the engine off at the knock sensor.

Cerridius

Ok I'll report back with any new info.

Cerridius

Ok I tested all 3, so..

KS wire Key on (car off) 4.78V
KS wire Car on only went to 4.81V
TPS plug was 5.05v with key on (car off)
MAP plug was 5.05v with key on (car off)

So something is up with the KS wire or something. Going to try swapping in a different knock module next.

Cerridius

Swapped in my GFs knock module. Voltage is 4.89 with the car on. Hers was the same way though with 4.89v

Took her car for a drive. She gets 0 knock retard te entire time and her knock count was like at 1406 the whole time. I'm still getting the same knock retard at WOT (4*) and knock counts up to 33,000.....

Idk I'm trying some octane boost now and I changed my MAP pigtail. Gonna go for another test drive. I guess if this doesn't work I may try uploading my old tune. With this new tune it seems like the drivability got worse.

Cerridius

Uploaded my old tune. No change. Still getting knock. If i just sit still and rev it I get like 40,000+ counts of knock.

Don't know if its real or false knock.

Just gonna put the other tune back on and live with it for now. Can't figure it out.

slopokrodrigez

With a jumper cable, add a temporary ground to the outside of the knock sensor.