PWM issue?
PWM issue? Hi,
I am trying to correct an issue I am having on my swap.
Car is 1987 Cadillac Brougham with a 4.8 and a 4L60E transmission and 2;73 gears.
I don't have a RPM gauge
2 things that are important to mention.
I cannot scan the PCM but the car runs fine otherwise.
When I bough the transmission the oil was really black so I flushed it until the colour was red. Did not change the filter yet
The issue is:
when I am on the highway at 60-75 mph and I press the accelerator slightly I feel and hear the RPM drop. If I press further the transmission shifts.
If I let the throttle go after the RPM drop, they rise again. I think it does that after I use the car a few miles. I read the converter locks only when transmission is warm enough.
Once or twice I noticed the transmission shifted hard but I am not sure if it was 1-2 or 2-3. Probably 1-2 since it was in the city.
First of all is this normal? Can I use the car another 6000 miles until winter comes and then I check the problem?
If not I'd like to know what are the minimum parts I should buy to fix this. I know the best is to scan the PCM and do more diagnostics but it does not work.
I want to buy a filter and the Sonnax valve and sleeve for the PWM. I know I could just block it but I understand it might cause further damage to weak elements.
What else do you recommend considering I am REALLY tight with money.
I was thinking about that harness in the transmission too.
Any advice is very welcome.
P.S. I checked all connexions on the PCM.
I am trying to correct an issue I am having on my swap.
Car is 1987 Cadillac Brougham with a 4.8 and a 4L60E transmission and 2;73 gears.
I don't have a RPM gauge
2 things that are important to mention.
I cannot scan the PCM but the car runs fine otherwise.
When I bough the transmission the oil was really black so I flushed it until the colour was red. Did not change the filter yet
The issue is:
when I am on the highway at 60-75 mph and I press the accelerator slightly I feel and hear the RPM drop. If I press further the transmission shifts.
If I let the throttle go after the RPM drop, they rise again. I think it does that after I use the car a few miles. I read the converter locks only when transmission is warm enough.
Once or twice I noticed the transmission shifted hard but I am not sure if it was 1-2 or 2-3. Probably 1-2 since it was in the city.
First of all is this normal? Can I use the car another 6000 miles until winter comes and then I check the problem?
If not I'd like to know what are the minimum parts I should buy to fix this. I know the best is to scan the PCM and do more diagnostics but it does not work.
I want to buy a filter and the Sonnax valve and sleeve for the PWM. I know I could just block it but I understand it might cause further damage to weak elements.
What else do you recommend considering I am REALLY tight with money.
I was thinking about that harness in the transmission too.
Any advice is very welcome.
P.S. I checked all connexions on the PCM.
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
Without a code scan, we are kinda guessing here.
Strange that the RPM drops when you press the gas; it could be that the TCC is slipping and when you give gas the PCM/Trans is increasing line pressure which stops the slipping and drops the RPM. That would be BAD - the TCC will quickly wear out from the slipping.
Installing the Sonnax PWM valve and sleeve is expensive and tricky; the necessary reamer tool is $120 and may require practice to use correctly; plus $35 for the valve.
I would suggest just installing an on/off TCC valve, e.g. the "1870 Fitxall" for $13:
http://hptransparts.com/techpak-fitz...0-a74741q.html
I have not heard of this damaging weak components; just the opposite - the TCC in the converter is likely to last longer.
Strange that the RPM drops when you press the gas; it could be that the TCC is slipping and when you give gas the PCM/Trans is increasing line pressure which stops the slipping and drops the RPM. That would be BAD - the TCC will quickly wear out from the slipping.
Installing the Sonnax PWM valve and sleeve is expensive and tricky; the necessary reamer tool is $120 and may require practice to use correctly; plus $35 for the valve.
I would suggest just installing an on/off TCC valve, e.g. the "1870 Fitxall" for $13:
http://hptransparts.com/techpak-fitz...0-a74741q.html
I have not heard of this damaging weak components; just the opposite - the TCC in the converter is likely to last longer.
Thanks for the answer,
I wouldn't do the reaming myself. I'd remove the valvebody and bring it to a transmission expert in my area.
I was saying it might damage something because I read using the on\off valve causes increased pressure to the converter. But that is what I read. Automatic transmission are black magic to me.
I'll wait for the answer of that transmission expert. If he's willing and has the tools to ream the valve body I will buy the proper valve, otherwise only the on/off valve. ANyways, given the colour of the transmission fluid that was in there who knows how long it will still last.
By the way, which wiring harness should I buy? Are some better than others?
I wouldn't do the reaming myself. I'd remove the valvebody and bring it to a transmission expert in my area.
I was saying it might damage something because I read using the on\off valve causes increased pressure to the converter. But that is what I read. Automatic transmission are black magic to me.
I'll wait for the answer of that transmission expert. If he's willing and has the tools to ream the valve body I will buy the proper valve, otherwise only the on/off valve. ANyways, given the colour of the transmission fluid that was in there who knows how long it will still last.
By the way, which wiring harness should I buy? Are some better than others?
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
I would welcome an expert correcting me, but I still think the on/off TCC valve will extend the life of your converter precisely because the pressure is higher. Many aftermarket converters also recommend an on/off valve. Think about the clutch in a manual transmission car; it will last longer if it is quickly engaged and disengaged (within reason) and wears quickly if the user lets it slip for verrrry slow enagements. Granted the stock converter is designed for PWM TCC, but will last even longer with an on/off TCC. The entire purpose for PWM TCC is a super-smooth-undetectible engagement of the TCC. Most of use prefer to actually feel it engage.
I suspect all "brands" of wiring harness are all made by one or two shops in China, so no big difference. Your trans shop will get it through their distributor and it will cost them around $30 with the attached TCC solenoid.
I suspect all "brands" of wiring harness are all made by one or two shops in China, so no big difference. Your trans shop will get it through their distributor and it will cost them around $30 with the attached TCC solenoid.
I have not ordered all the parts yet because I am still thinking if I should replace my plastic pistons on the accumulators with aluminum ones or not. I tend to do want to do it. The question is if I do replace them should I get new springs or can I re-use the old ones?
On one hand I am happy I have not found any chunks of metal inside. Just some aluminum dust muck on the bottom of the oil pan. I hope by replacing these parts I will be able to mke it last another 20k-30k miles, about 3-4 summers.
I did not see any big play in the PWM valve but I am replacing it with the Teckpak one anyways.
What I found is that one o-ring on the pressure switch manifold was barely hanging there and the plastic is bent. So I am replacing that. It was a good thing I decided to remove it to check it because initially I was just going to leave it on the valve body
But I think it will take me 3 weeks to put everything back because I won't have the time and it's not something I would like to rush.
On one hand I am happy I have not found any chunks of metal inside. Just some aluminum dust muck on the bottom of the oil pan. I hope by replacing these parts I will be able to mke it last another 20k-30k miles, about 3-4 summers.
I did not see any big play in the PWM valve but I am replacing it with the Teckpak one anyways.
What I found is that one o-ring on the pressure switch manifold was barely hanging there and the plastic is bent. So I am replacing that. It was a good thing I decided to remove it to check it because initially I was just going to leave it on the valve body
But I think it will take me 3 weeks to put everything back because I won't have the time and it's not something I would like to rush.
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Well...I wasn't expecting that but things turned worse than they were.
I lost 1st gear, I got a check engine light and I cannot read the codes either so I am really stuck.
I changed the 3 pistons, separator plate, Fitzall valve, harness, replaced check ***** with plastic ones.
I thought it was just the vaseline that I used for the check ***** but even after 15-20 minutes of driving around the block it still won't engage first gear. It seems to take off in 2nd.
I guess the next step is to find a PCM that allows me to read the codes but that is some extra money that I don't so it's going to have to wait a while, maybe after winter.
I lost 1st gear, I got a check engine light and I cannot read the codes either so I am really stuck.
I changed the 3 pistons, separator plate, Fitzall valve, harness, replaced check ***** with plastic ones.
I thought it was just the vaseline that I used for the check ***** but even after 15-20 minutes of driving around the block it still won't engage first gear. It seems to take off in 2nd.
I guess the next step is to find a PCM that allows me to read the codes but that is some extra money that I don't so it's going to have to wait a while, maybe after winter.
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Verdad Gallardo Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
Sorry to hear about your troubles.
Most chain auto stores (in the US anyway) will let you scan for codes at no charge in their parking lot. Or you can take the scanner home for a free rental for a few days after leaving a deposit (typically a high $300-$400).
Off hand, it sounds like an electrical problem with the solenoids or the internal wiring harness. Should be easy to fix, especially once we know the code #.
BTW - Thanks for your useful post about how to install the Teckpack Fitzall 1870 fix valve in slayer_taunu's thread.
Most chain auto stores (in the US anyway) will let you scan for codes at no charge in their parking lot. Or you can take the scanner home for a free rental for a few days after leaving a deposit (typically a high $300-$400).
Off hand, it sounds like an electrical problem with the solenoids or the internal wiring harness. Should be easy to fix, especially once we know the code #.
BTW - Thanks for your useful post about how to install the Teckpack Fitzall 1870 fix valve in slayer_taunu's thread.
It is the least of the things I could do after all the help I received from you and other forum members, share anything from my experience that could help or guide somebody else.
My friend has a scanner but my PCM has a problem, I cannot communicate with it, I tried another one and with the other one I was able to communicate.
But the good news is I was able to solve my problem. I am embarassed to say this but the connector on the transmission wasnèt properly plugged in.
I tried the car and the transmission does not seem to acy funny anymore on the highway (dropping revs when I lightly press the accelerator).
Thanks again for the help and the great advice.
My friend has a scanner but my PCM has a problem, I cannot communicate with it, I tried another one and with the other one I was able to communicate.
But the good news is I was able to solve my problem. I am embarassed to say this but the connector on the transmission wasnèt properly plugged in.
I tried the car and the transmission does not seem to acy funny anymore on the highway (dropping revs when I lightly press the accelerator).
Thanks again for the help and the great advice.
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
Hey, great to hear that you got it all working. 
And it takes a REAL man to admit to such a silly mistake.
Guess we'll never know if the connector was the only problem or the TCC valve was also acting up.
In any case I'm sure you learned a lot about transmissions and fortunately didn't spend too much money on it.
And it takes a REAL man to admit to such a silly mistake.
Guess we'll never know if the connector was the only problem or the TCC valve was also acting up.
In any case I'm sure you learned a lot about transmissions and fortunately didn't spend too much money on it.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
This has an OBD-1 ECM, right...?
With key-on-engine-off, if you short pins A and B together on the 12-pin ALDL socket, the ECM will flash the CEL, you count the flashes to get the DTC codes...
the ECM will flash each DTC as a pair of digits, it does each pair 3 times, it goes thru all the DTC list and then starts at the top again... 12 will always be the first code (no pulse from CKP sensor).
With key-on-engine-off, if you short pins A and B together on the 12-pin ALDL socket, the ECM will flash the CEL, you count the flashes to get the DTC codes...
the ECM will flash each DTC as a pair of digits, it does each pair 3 times, it goes thru all the DTC list and then starts at the top again... 12 will always be the first code (no pulse from CKP sensor).
Hey, great to hear that you got it all working.
And it takes a REAL man to admit to such a silly mistake.
Guess we'll never know if the connector was the only problem or the TCC valve was also acting up.
In any case I'm sure you learned a lot about transmissions and fortunately didn't spend too much money on it.
And it takes a REAL man to admit to such a silly mistake.
Guess we'll never know if the connector was the only problem or the TCC valve was also acting up.
In any case I'm sure you learned a lot about transmissions and fortunately didn't spend too much money on it.
I am sure the TCC was acting up though, the connector was properly "connected" if I can say that. I remember it took a bit of persuasion on it before I removed the inside wiring in the transmission so I could replace it.
I did learn a very little bit though, this is true. that's the real fun part of it. Hopefully the rest of it will last another 20k miles at least, considering the initial colour of the transmission fluid, which was more suitable for a Guinness beer, minus the foam of course!
This has an OBD-1 ECM, right...?
With key-on-engine-off, if you short pins A and B together on the 12-pin ALDL socket, the ECM will flash the CEL, you count the flashes to get the DTC codes...
the ECM will flash each DTC as a pair of digits, it does each pair 3 times, it goes thru all the DTC list and then starts at the top again... 12 will always be the first code (no pulse from CKP sensor).
With key-on-engine-off, if you short pins A and B together on the 12-pin ALDL socket, the ECM will flash the CEL, you count the flashes to get the DTC codes...
the ECM will flash each DTC as a pair of digits, it does each pair 3 times, it goes thru all the DTC list and then starts at the top again... 12 will always be the first code (no pulse from CKP sensor).
Normally it would have been the ALDL connection, I only kept it for the electronic climate control which does not work anyways. I might have taken out too many wires and I don't have an A/C compressor yet anyways....
Oops, I read the post too fast...
I see you mention the ALDL socket, I had OBD-1 in my head which I think it isn't. But I may be wrong, I will check in my manual which is in the trunk of the car
I see you mention the ALDL socket, I had OBD-1 in my head which I think it isn't. But I may be wrong, I will check in my manual which is in the trunk of the car