Chasing where the power loss is below 5500 944S
05-26-2016, 10:35 AM
#1
Chasing where the power loss is below 5500 944S
Rather than continuing on my older thread I am starting a new one just to document and see suggestions on where the issue is.
Problem: Power inconsistent or "down" below 5500. Once you hit that it kicks you in the pants...usually a dramatic change
- Sometimes adjusting my foot on the gas pedal seems to help...as if the air is off. I feel no change at WOT below 5500 RPM.
- Replaced so far:
On my list to change:
If it turns out not to be any of these could it be the cam followers? It does tick a lot once it warms up...kind of noisy. I tested all of them before head assembly and all were good.
Chris
Problem: Power inconsistent or "down" below 5500. Once you hit that it kicks you in the pants...usually a dramatic change
- Sometimes adjusting my foot on the gas pedal seems to help...as if the air is off. I feel no change at WOT below 5500 RPM.
- Replaced so far:
- Cam Sensor
- Timed engine
- O2 Sensor (tried unpluged and it was worse when cold)
- AFM (most recent change)
- Knock Sensors
- Injectors sonically cleaned and back to spec
- FPR
- Hard vac lines
On my list to change:
- TPS - maybe this is the problem and it is sticking open (as if at idle)?
- Reseal throttle body
If it turns out not to be any of these could it be the cam followers? It does tick a lot once it warms up...kind of noisy. I tested all of them before head assembly and all were good.
Chris
Last edited by CVR_Rally; 05-27-2016 at 07:04 AM.
05-26-2016, 10:40 AM
#2
Rainman
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I don't recall if it was mentioned in the other thread - "timed engine" means cam timing with the dial gauge? Or just verifying on the cam gear?
My experience with a good running 944S is that the kick in the pants comes at 4000rpm or so.
Perhaps the cam timing is still a little off?
My experience with a good running 944S is that the kick in the pants comes at 4000rpm or so.
Perhaps the cam timing is still a little off?
05-26-2016, 10:47 AM
#3
I don't recall if it was mentioned in the other thread - "timed engine" means cam timing with the dial gauge? Or just verifying on the cam gear?
My experience with a good running 944S is that the kick in the pants comes at 4000rpm or so.
Perhaps the cam timing is still a little off?
My experience with a good running 944S is that the kick in the pants comes at 4000rpm or so.
Perhaps the cam timing is still a little off?
05-26-2016, 11:49 AM
#4
It was taught in the factory school, but never documented anywhere, that timing the engine with the dial indicators only sets the starting point for the relationship between the exhaust cam and the crankshaft. Once that is established, you must fine tune the exhaust cam timing by a reiterative process of adjusting the timing a few degrees at a time, until the car both has a stable idle and "comes alive" at 4000 rpm.
After rebuilding a 944S engine one time, it took me an extra ten hours to dial in the cam for proper operation.
After rebuilding a 944S engine one time, it took me an extra ten hours to dial in the cam for proper operation.
05-26-2016, 05:49 PM
#5
It was taught in the factory school, but never documented anywhere, that timing the engine with the dial indicators only sets the starting point for the relationship between the exhaust cam and the crankshaft. Once that is established, you must fine tune the exhaust cam timing by a reiterative process of adjusting the timing a few degrees at a time, until the car both has a stable idle and "comes alive" at 4000 rpm.
After rebuilding a 944S engine one time, it took me an extra ten hours to dial in the cam for proper operation.
After rebuilding a 944S engine one time, it took me an extra ten hours to dial in the cam for proper operation.
Chris
05-26-2016, 06:39 PM
#6
Rennlist Member
What about the knock sensors giving false readings?
On some other cars I know that the ECU will ignore their input past a certain (high) RPM because the sensors are exposed to a lot of mechanical noise and can't accurately detect real knock. Not sure if the 16v DMEs are also set up that way, but if they were, maybe 5000 rpm is the point where the timing is allowed back in.
On some other cars I know that the ECU will ignore their input past a certain (high) RPM because the sensors are exposed to a lot of mechanical noise and can't accurately detect real knock. Not sure if the 16v DMEs are also set up that way, but if they were, maybe 5000 rpm is the point where the timing is allowed back in.
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05-27-2016, 12:44 AM
#8
First try a higher octane fuel. The DME of the S had a fault that was corrected in the S2. The S model's DME had a 3 degree timing retarding feature that once knock was sensed the timing was retarded and then slowly advanced in .75 degree increments as the knocking ceased. The rate of return to normal curve required time so that the retardation remained effective over a relatively wide speed range. The S2 with the "Adaptive Knock Regulation" mod to the DME also retards 3 degrees with knocking. When knock stops the timing advances in.75 degree increments if needed but can go straight to full advance bypassing all the .75 degree increments unless needed. This according to my Factory 1989 944S2 Service Information.
05-27-2016, 07:01 AM
#9
First try a higher octane fuel. The DME of the S had a fault that was corrected in the S2. The S model's DME had a 3 degree timing retarding feature that once knock was sensed the timing was retarded and then slowly advanced in .75 degree increments as the knocking ceased. The rate of return to normal curve required time so that the retardation remained effective over a relatively wide speed range. The S2 with the "Adaptive Knock Regulation" mod to the DME also retards 3 degrees with knocking. When knock stops the timing advances in.75 degree increments if needed but can go straight to full advance bypassing all the .75 degree increments unless needed. This according to my Factory 1989 944S2 Service Information.
I also checked the manual back then and sure enough it recommends high obtain already. I'm going to be marking the cam and making adjustments.
Currently it does idle pretty smoothly. I should take some video because that's always better than trying to translate into word the on/off power you get.
05-27-2016, 09:06 AM
#10
Well so much for the knocking theory.
"Sometimes adjusting my foot on the gas pedal seems to help...as if the air is off. I feel no change at WOT below 5500 RPM." I know you changed out the AFM but did you check the wiper in the AFM? If the track is worn the wiper arm can be repositioned to fresh material. There are write ups on this repair.
"Sometimes adjusting my foot on the gas pedal seems to help...as if the air is off. I feel no change at WOT below 5500 RPM." I know you changed out the AFM but did you check the wiper in the AFM? If the track is worn the wiper arm can be repositioned to fresh material. There are write ups on this repair.
05-27-2016, 04:48 PM
#11
Small update.
I got some seat time after the new AFM and timing setup by going to Lime Rock for PWC (1st race just finished).
It isn't 'that' bad and does seem to kick in at 4K but there still is a kick at 5500. I have noticed throttle response is much better after the timing setup and I can rev match much better than before.
I have a reseal kit for the throttle body and may still replace the TPS but I want to test it first.
I do appreciate everyone's input!
Chris
I got some seat time after the new AFM and timing setup by going to Lime Rock for PWC (1st race just finished).
It isn't 'that' bad and does seem to kick in at 4K but there still is a kick at 5500. I have noticed throttle response is much better after the timing setup and I can rev match much better than before.
I have a reseal kit for the throttle body and may still replace the TPS but I want to test it first.
I do appreciate everyone's input!
Chris
05-27-2016, 08:20 PM
#12
Throttle reseal and TPS replacement are a pain on the S - I think you'll end up taking the intake manifold off with the throttle and J-tube attached to do it. I did. In addition to testing the TPS electrically, I'd try to check for leaks first.
Seems unlikely to me that either would be your root cause, though. If the DME gets an idle command from the TPS while measuring an open AFM door, I'm not sure what happens, but I'd venture to guess it would ignore the TPS. If not it would probably just stall. Anyone know for sure?
The kick in the seat, in my experience, is more like 3800 rpm, and you're not left wondering if it's happening. A kick at 5500 I have not noticed - I'll check it out.
Seems unlikely to me that either would be your root cause, though. If the DME gets an idle command from the TPS while measuring an open AFM door, I'm not sure what happens, but I'd venture to guess it would ignore the TPS. If not it would probably just stall. Anyone know for sure?
The kick in the seat, in my experience, is more like 3800 rpm, and you're not left wondering if it's happening. A kick at 5500 I have not noticed - I'll check it out.
05-31-2016, 11:46 PM
#14
Chris
06-01-2016, 03:37 PM
#15
Addict
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Did you resolve the low compression? Check leakdown?
I was on the timing because I thought there was no way the compression would be low like that across all four jugs. I was thinking valve timing was keeping a valve open during part of the compression stroke and killing your compression PSI. A leakdown would be interesting. The Harbor Freight tester is not totally useless.
I was on the timing because I thought there was no way the compression would be low like that across all four jugs. I was thinking valve timing was keeping a valve open during part of the compression stroke and killing your compression PSI. A leakdown would be interesting. The Harbor Freight tester is not totally useless.