Nearly all new but still has acceleration issues

atomicoverload · 12-25-2010, 02:46 PM

I have an 85.1 and have driven other 944 N/A's. The acceleration of the other cars was smooth and quick, but no matter what I have done to my car it still feels like accelerating is a struggle. It had some hesitation issues which have been eliminated, but from day one it has always felt the same. Don't get me wrong-it runs well, just not like I know it should and am out of ideas.

I would describe the problem as while the other 944's feel like they are being pushed when you hit the gas, mine feels like it's being pulled while dragging something. We might go just as fast, but mine seems to have to work harder to do it.

Work done: Full engine rebuild (except lifters which were good) including all new sensors, all new vacuum hoses (took to mechanic after and had a smoke machine ran on it), new Bosch fuel injectors, new MAF, new fuel pump/filter, fuel damper, fuel regulator, replaced ECU, new clutch, reconditioned torque tube, replaced transmission, new CAT, new O2 sensor, coil, wires, cap rotor, on and on. Even replaced front and rear engine wiring and alternator. Checked fuel pressure which was good. Compression has always been good. Replaced throttle body with no change. Every gasket replaced. I even checked the gas tank filter which was clean. Always run premium gas. Replaced front and rear wheel bearings.

My thought all along is that it is either a vacuum or fuel issue. All the vacuum lines were replaced and smoke tested so unless something is hiding from me I can rule that out. Fuel pump, fuel filter, fuel injectors replaced and fuel pressure is good so the only thing I am left with is fuel lines. But can this be the problem? I will note that the fuel delivery line to the fuel damper has some visible cracking and I had to cut out and splice a section. Still some cracking though. For the love of God-any other ideas?

HondaDustR · 04:19 PM

Are the brakes dragging, or is the parking brake jammed up in the rear?
The catalytic converter could be melted or plugged or the muffler could be collapsed inside. Is your FQS on the DME set to default? FQS - Fuel Quality Switch Is the o2 sensor getting a good ground through the exhaust system to the engine/chassis/DME?

One thing you could try that might rule out something obvious is to make an o2 sensor bypass harness, which will keep the heater connected, while letting you tap into the o2 sensor signal with a voltmeter to measure it while driving. The o2 signal output in open loop mode is very stable and representative of the mixture as much as a narrow band sensor could be, but the heater must be energized. It jumps around more or less meaninglessly when the DME is receiving the signal and constantly correcting for it. Connect a multimeter to the signal wire on the sensor and to a good ground and drive. At least you'll see if you are running very lean or rich. You should see up around the .8v range at full throttle. If it's rich enough to run into the mid .9's at WOT, it might be too rich. If it's less than .6v at WOT, it's definitely too lean. The DME runs in open loop mode when at WOT anyway, so having the sensor disconnected from the DME would not change the conditions for a test at WOT and the sensor connected.

Make sure your throttle switch is working, too. Mine felt kind of anemic until I fixed the switch. The part throttle maps on the stock tuning are pretty anemic feeling and do not do well at high speeds and/or loads when the WOT switch isn't activating the WOT maps. Throttle Position Switch - Information, Troubleshooting, Replacement, and Adjustment Vacuum leaks are also bad for these motors, but since you've replaced and checked just about everything, it should be ok. Check the dispstick seal, oil cap seal, rear balance shaft housing plug seals (if they for some reason weren't replaced), intake J boot for cracks...anything that could leak vacuum into the intake or the crankcase.

You also mentioned the motor has been rebuilt. Did this include new rings? How many miles on the motor and how was it broken in? Does it smoke at all? (new rings take time to break in) If the rings aren't sealed very well yet, the blowby will get into the intake through the breather system and dilute the air that has already been metered by the AFM, making the motor run lean. Is there oil in the throttle body? That points to excessive air exchange through the crankcase breather due to blowby or a leak into the crankcase from anywhere that could leak vacuum. The crankcase has a pretty good vacuum pulled on it in a healthy motor. The breather system is pretty overengineered. Take the oil cap off and seal your palm over the openning while the motor is running to see if it's pulling a decent vacuum. Usually a vacuum leak will give a rough unstable idle as well.

AA_Ezra · 12-25-2010, 07:23 PM

Well, When i put on new belts on my car they were a little on the tight side because i didn't use the proper tool at the time and the car felt sluggish just as you described and then after a while it started to drive like normal.

I did the belts again and didn't notice the problem as bad,

Just my 2 cents.

like honda duster has mentioned maybe the combination of many new parts like bearings in the torque tube and piston rings and any other items that make a small amount of friction and need to be broken in.

Jrboulder · 12-25-2010, 07:29 PM

And you did this on your own without the help of this forum?

That!s awesome!

atomicoverload · 09:42 AM

Thanks for the response. Brakes feel fine. Front brakes are new. Parking break doesn't seem to be an issue. Cat is new replacing a second used one and have had 2 different mufflers on there. The whole exhaust has been changed twice from the original.

FQS is set to default and have tried different settings with little to no change. The O2 has been replaced twice and the wiring was swapped when I redid the engine harness. I also was running a wideband O2 sensor for a while.

Changed the TPS with new with no change. On the new ones the mounting holes were offset so I had to Dremel them out to fit. Always bugged me because it was hard to get the click just right so I switched back to different used one. No change any which way. Every seal and gasket has been replaced and other than the supply fuel line there is no cracking anywhere. Replaced balance shaft plugs. They disintegrated when we took them out for the rebuild. Never thought about the dipstick or oil cap seal, but what would that do other than leak oil?

Car did the same before and after the rebuild. New rings. Put about 1k on it very conservatively to break it in then changed oil and have been driving it normally since. No oil in the throttle body but since the engine rebuild there is some residue in the J-boot I noticed. Very minimal. I will try that with the oil cap.

The idle is interesting because it is usually pretty solid, but sometimes I'll drive around for a while and it will hunt a little bit around 850-900. Drive around some more and it will peg at 1000. I can hit 5 stop lights with no change and the 6th one it will hunt around then 2 stops later its gone again. Could this be the aluminum flywheel? It was worse before and I replaced the throttle body with another used one and it was a lot better. Also has the used TPS.

I did not replace the camshaft or lifters when we did the rebuild. My friend who is the mechanic was the brains behind the operation, but he said both looked good. The camshaft did look good, but I have always wondered if after 150+k on a cam if there is enough wear that you may not be able to see but is actually enough to make it "tired" so to speak.

The struggle to me seems to be fuel or vacuum related, but I have to wonder about the cam shaft as well. I've ruled out nearly everything vacuum related so I will change the fuel line which I need to do anyways.

Belts have been readjusted a few times since the rebuild. It does run better the more I drive it and probably have about 3k on the rebuild. I'm wondering if there is a "sweet spot" of mileage on a rebuild that once you get to that point you pretty much know you've broken it in.

I have used many forums, but this is the first time I have joined one. Couldn't have made it this far without them.

HondaDustR · 12-26-2010, 12:07 PM

My rebuild didn't really feel "mature" until around 10K miles. The dipstick and oil fill cap seals will not leak oil because oil never goes up there, but they will leak crankcase vacuum.

Sounds like you might have a wonky electrical connection or something. It could also be a vacuum leak lurking around somewhere in a strange or concealed place, or that it leaks randomly from maybe a small crack or something. If the cam is out of time a tooth it could do the same thing. I like to also test things straight from the DME plug, since any wiring problems will show up as well. It's also good for monitoring and testing for troubleshooting, since if you slide the cover off the connector, multimeter test leads will fit into the pin block cells from the back to contact the pins while allowing the DME to be plugged in and run. Useful for o2 sensor monitoring, AFM return signal monitoring, rigging up a manual WOT switch, etc. which I have done on occasions chasing weird problems like yours.
DME Connector 35-pin

atomicoverload · 12-26-2010, 12:50 PM

That is good to know. I was thinking there was a seal at the bottom of the dipstick, but forgot it is a welded piece. I will try the cap test though.

Electrical has been a thought, but after replacing both front and rear engine wiring not really sure what it could be being the problem didn't change. I even replaced both battery cables.

I tested the WOT on the DME and it was good. Definitely weird. You'd think if you replace everything with new it would be like new, but that is the lesson I have learned from his project.

In your experience, do you think it could be fuel line related? When I had it smoke tested I had them check the timing too and it was spot on.

HondaDustR · 01:19 PM

Oh, now I see. There is a seal on the dipstick itself, but there is also a seal where the dipstick tube meets the block, which will leak some oil if not sealing well.

It could certainly be a fuelling issue, but the only thing I can think of to check if the pressure is good is the flow rate. Fuel Pump Delivery Rate Checking

From there, it could literally be anything that is possible to be defective, intermittently malfulctioning, or an error in assembly. Just how bad does it feel as far as down on power? Did the motor have alot of miles on it before the rebuild and was down on power from wear, whereas now it's down on power because it's not completely broken in? But you said compression tests good, so I don't see that as a problem. Ultimately, since these are mass produced motors, some will just be better toleranced than others and it's possible maybe the one you have just isn't much of a golden sample. What oil weight are you using? I just went from 20W-50 Brad Penn to 0W-30 Castrol syntec euro formula for the winter and the engine feels much livelier not having to slug around heavy oil in the cold. It is critical to run non synthetic for at least the first 1500 miles on a rebuild, and preferably the first 5000 in my opinion. Rings can take as long as 10K to seat 100%.

Your altitude sensor if equiped isn't falsely indicating that you are at high altitude, is it? http://www.the944.com/altitude.htm

Is your DME is correctly coded for your equiped engine if running a late DME? http://www.motronic.ws/4in1.htm

atomicoverload · 12-26-2010, 02:07 PM

I pulled the oil cap off and put my hand over it and I don't feel it pulling any vacuum. I can feel a little air exchange, but certainly nothing to the effect of any suction on my hand.

After the engine rebuild and the mods and fixing a few vacuum lines, the power has increased dramatically, but is probably on par with an average 944 when it should be better. I wish you could drive it because you'd know exactly what I was talking about. Power is good, runs good, but yours would feel different. Smoother. Yeah, it is possible I got the one made on Monday instead of Wednesday, but I've replaced everything with Wednesday parts so not sure why the problem persists.

I thought about the altitude correction box and ran it without it even plugged in and there was no difference. I wonder though if it is stuck to lean the fuel if it being unplugged would have the same effect by default.

I have an '87 DME and '87 MAF. The problem was worse before I switched. Looking at the coding tables you sent it seems all US cars are the same except if from CA which has a coding plug. If there was no difference between switching DME's other than the later model ran better I'm not sure what effect this would have with or without the coding plug.

I ran non synthetic for about 1000mi before I switched to Mobile 1.

atomicoverload · 12-26-2010, 03:24 PM

One thing I will say about this car which may be a clue is that the acceleration is better the slower and more even I push on the pedal. Flooring it is counter productive. The car doesn't bog down or want to stall or anything like that, but if I give gas too fast it isn't directly proportional to the acceleration you would expect. Like I need to "lead up to it" so to speak for greater acceleration. It's very subtle but it is definitely there.

guru944 · guru944's Garage

Atomicoverload:

Did you check for leaks in your exhaust system. Between the exhaust header and cylinder head, the lower 2 piece feed pipe and the Catalytic Convertor. Sometimes the "Cat" Gets clogged. Or small spider cracks develop "Hair strand thin"where vacuume and gases escape. Some signs are white patches around flanges. Torque will suffer especially at the bottom end of the rpms. Had quite a few when I redid my head. I ended up Re-Tig welding all of mine (time consuming).(See pics below)

The 1988 and later vehicles have better exhaust Manifolds.

Also Thermo wrapped the header to improve power and reduce underhood heat up to 75%.
But all is well and quiet.

Hope this reply/post was helpful.

Later.

atomicoverload · 12-26-2010, 04:40 PM

Thanks for the post guru944. I replaced the headers when I did the rebuild with some real nice late model ones, so no cracks, but it didn't have any effect either way. Wrapped my headers as well. The cat is new and replaced another used one I tried first. That's another maddening thing is I've completely replaced every component on the exhaust twice so I think I've ruled that out. My exhaust is still loud though. Doesn't matter which muffler or cat.

HondaDustR · 06:15 PM

Quote:

Originally Posted by atomicoverload

One thing I will say about this car which may be a clue is that the acceleration is better the slower and more even I push on the pedal. Flooring it is counter productive. The car doesn't bog down or want to stall or anything like that, but if I give gas too fast it isn't directly proportional to the acceleration you would expect. Like I need to "lead up to it" so to speak for greater acceleration. It's very subtle but it is definitely there.

I know what you mean. Kind of like having to follow the power curve closely with the throttle. I had noticed that with my old motor and never really figured out what was causing it since it was relatively subtle and intermittent. I don't notice it with my current motor.

Does it feel like if you get ahead of the power curve with the throttle it degrades whether or not you actually hit WOT, or do you only notice it take a step back in power only if you floor the pedal, activating the WOT switch?

Quote:

Originally Posted by guru944

Also Thermo wrapped the header to improve power and reduce underhood heat up to 75%.

guru944, nice work, but from what I can see in the picture, that header wrap is only good for up to 70% reduction in temps.

atomicoverload · 12-27-2010, 03:54 PM

Exactly. Doesn't matter whether I hit WOT or not. Kind of like I need to sync depressing the peddle with the power curve and if I push it too fast it flattens out a little bit. WOT is flat. The other cars I drove were not this way and I think whatever the cause this is really what the problem is.

atomicoverload · 12-27-2010, 05:04 PM

Hmmm. This is something curious I was thinking about-I changed to an '87 ECU and MAF long before I did any of the performance upgrades or engine rebuild. If you go to FRWilke www.the944.com ©1999 FR Wilk and go to Fuel Injectors, on the surface there seems to be quite a difference between early and late injectors. Up until I did the engine rebuild I didn't change the injectors and when I did they were Bosch 0 280 150 159, sold to me as for a 944 but apparently they are for a Ford Escort. Bastards. The correct late model PN# is 0 280 150 158 and if you go here http://www.bulletperformanceracing.com.au/Bosch%20Fuel%20Injectors%20Table%20150.html and compare the 2 they are quite different as well with the Escort model being nearly identical to the early Porsche 944 0 280 150 201.

The million dollar question is because I have the late ECU, could the problem be it wants late model fuel injectors too, but what it's getting is early model injectors?

Slam · 11:06 AM

Did you put in a new auxiliary air valve? If you reused the old one, it may be stuck partially open, so you've got a lean surge problem.

If you paired the late DME with the late AFM there should be no problem. Did you have the AFM apart to refurb the wiper tracks? Oh - wait. I just re-read your first post. "New AFM."

You may want to put a late cam in. They're a little more aggressive, and perhaps the late DME would be happier with one in the car (although that's a long shot. My 83 has a late cam and early DME & AFM and runs fine).

atomicoverload · 12-30-2010, 04:11 PM

Thanks for the input. I did put in a new auxiliary valve but not by choice. Accidentally broke a nice chunk off the connector so I guess the car was trying to tell me something.

I was thinking about a late cam. Is it all late models or just '87 and later? I thought I read somewhere the '88 was the one to get.

Well, I replaced the injectors with late model ones today and it did smooth things out a bit. Nothing life changing, but definitely noticeable. Hard to tell if its the injectors or the fact one of my old ones had a cracked cap. I bought those about a year ago and know I did do it just now when I switched them.

The AFM was a reman and I took the cap off to make sure to see I didn't get screwed because that's kind of what it feels like, but strip is new.

I don't know what it means, but I have always had hesitation during acceleration in second gear. The rest of the gears are fine, or at least I don't notice it, but 2nd gear in particular is an issue.

HondaDustR · 12-31-2010, 02:21 PM

There seem to be a couple different pintle cap versions out there used on these injectors. The ones that witchhunter put on an extra set were not the same as the ones that were on my original set. The little cone shaped cutout was larger on the original injectors and frankly, it made a better spray pattern and ran a little smoother than the witchhunter rebuilds.

atomicoverload · 12-31-2010, 03:37 PM

Drove around some more today and I'm feeling the new injectors. The car does not seem to struggle as much, idles better, and acceleration is smoother. Definitely seems happier with the new injectors. Glad I went for it because I think that this was definitely part of the overall problem. I still have a nagging suspicion there is another component that is just not right or a fuel hose or vacuum leak. I'm contemplating buying the fuel line kit from Renlist, but am wary of the job. Looks like a pain to get to the supply hard line and I hate dealing with fuel issues.

I have a question if anyone knows, but is there any kind of conversion or mod for early models to install the late model center transmission mount? And would it even be worth it as far as reducing noise and vibration? I have an idea to mod it myself but don't want to reinvent the wheel.