Vibration/rough under load... bad dme? (long)
06-27-2002, 02:42 AM
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Three Wheelin'
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Vibration/rough under load... bad dme? (long)
I have an intermittent problem of the engine vibrating when under load/boost. The vibration seems to come and go. Often it seems that the presence of the vibration correlates with a high water temp (as high as the third bar on the gauge, not above it), but this is not always the case. When this vibration is present, it is most pronounced under high load (3rd+ gear, high rpm, full throttle). Basically, the engine runs rough and does not seem to get even combustion. However, it still seems to be making good power.
About 10,000 miles and four months ago I completed replacing all gaskets, hoses, rod bearings, seals, turbo, rebuilt injectors, yada yada. Since then, this problem has developed intermittently and become increasingly prominent. Other than the high altitude issues, I have not had any other engine related issues over the last 10,000 miles.
When off the throttle, even at very high rpms, there are no symptoms.
In the past week, I have replaced the number four injector (replaced spark plugs several thousand miles ago and cylinder 4 was much leaner than the rest, thus the injector suspicion), the spark plugs wires, and the spark plugs. None of these things seem to fix it. All the plugs looked a little lean, but they were consistent. They were definitely not white lean. I chalk this up to crappy California gas.
Right now, it seems most likely that it is either a intermittent head gasket leak, a fuel pressure problem, or a problem with the dme or the dme harness.
There is definitely no oil/coolant mixing or coolant loss. Oil usage seems to be between 1 quart per 1000 miles down to 1 quart per 400 miles under extreme use. Based on leakdown and compression tests I did 10,000 miles ago, I chalk this oil usage down to worn rings. Based on this information, it seems to rule out even intermittend head gasket failure.
I'd love to try borrowing someone elses 951 DME and KLR so that I could diagnose this further. If the DME and KLR are in your car, I would be happy to crawl under your dash, remove them, try them in my car, and then put the parts back in your car. I'd also be happy to bring some beer and help fix whatever ails your car.
As for my car, here are the motor specs:
'86 951, K26-8, LBE, 14 psi boost, SFR Turbo S chips, Wide fire head gasket, Garrity 190ksi head studs.
I have been wanting to do some track events, but as it is I don't feel comfortable subjecting the engine to full load lap after lap with it running rough.
Any ideas?
About 10,000 miles and four months ago I completed replacing all gaskets, hoses, rod bearings, seals, turbo, rebuilt injectors, yada yada. Since then, this problem has developed intermittently and become increasingly prominent. Other than the high altitude issues, I have not had any other engine related issues over the last 10,000 miles.
When off the throttle, even at very high rpms, there are no symptoms.
In the past week, I have replaced the number four injector (replaced spark plugs several thousand miles ago and cylinder 4 was much leaner than the rest, thus the injector suspicion), the spark plugs wires, and the spark plugs. None of these things seem to fix it. All the plugs looked a little lean, but they were consistent. They were definitely not white lean. I chalk this up to crappy California gas.
Right now, it seems most likely that it is either a intermittent head gasket leak, a fuel pressure problem, or a problem with the dme or the dme harness.
There is definitely no oil/coolant mixing or coolant loss. Oil usage seems to be between 1 quart per 1000 miles down to 1 quart per 400 miles under extreme use. Based on leakdown and compression tests I did 10,000 miles ago, I chalk this oil usage down to worn rings. Based on this information, it seems to rule out even intermittend head gasket failure.
I'd love to try borrowing someone elses 951 DME and KLR so that I could diagnose this further. If the DME and KLR are in your car, I would be happy to crawl under your dash, remove them, try them in my car, and then put the parts back in your car. I'd also be happy to bring some beer and help fix whatever ails your car.
As for my car, here are the motor specs:
'86 951, K26-8, LBE, 14 psi boost, SFR Turbo S chips, Wide fire head gasket, Garrity 190ksi head studs.
I have been wanting to do some track events, but as it is I don't feel comfortable subjecting the engine to full load lap after lap with it running rough.
Any ideas?
06-27-2002, 02:52 PM
#3
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Hey Steve -
I feel your pain...
Sounds to me like it's a vacuum leak. I know it sounds funny, but only under high load (high pressures in the intake) do you see the problem...
The lean condition on 4 is almost normal on these cars, but a vac leak would make it more pronounced.
Have you tried testing the intake under pressure?
Cut a fuel filter in half with a hacksaw - and remove the fittings. You'll find that an american threaded air chuck for a compressor tool fits perfectly in one! Clamp that down into the j-boot where the air flow meter is (or used to be) and pressurize to like 8-10psi. Spray all connections with a mixture of dish-soap and water. Watch for bubbles.
It COULD be a fuel delivery issue, or perhaps the KLR retarding the ignition a LOT due to what it thinks is knocking... Have you checked the KLR fault codes at the test connecter?
HTH!
I feel your pain...
Sounds to me like it's a vacuum leak. I know it sounds funny, but only under high load (high pressures in the intake) do you see the problem...
The lean condition on 4 is almost normal on these cars, but a vac leak would make it more pronounced.
Have you tried testing the intake under pressure?
Cut a fuel filter in half with a hacksaw - and remove the fittings. You'll find that an american threaded air chuck for a compressor tool fits perfectly in one! Clamp that down into the j-boot where the air flow meter is (or used to be) and pressurize to like 8-10psi. Spray all connections with a mixture of dish-soap and water. Watch for bubbles.
It COULD be a fuel delivery issue, or perhaps the KLR retarding the ignition a LOT due to what it thinks is knocking... Have you checked the KLR fault codes at the test connecter?
HTH!
06-27-2002, 03:14 PM
#4
Three Wheelin'
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Thanks!!
[quote]Originally posted by Toolmaster:
<strong>I feel your pain...</strong><hr></blockquote>
I feel dirty when I drive it hard.
[quote]Originally posted by Toolmaster:
<strong>Sounds to me like it's a vacuum leak. I know it sounds funny, but only under high load (high pressures in the intake) do you see the problem...
The lean condition on 4 is almost normal on these cars, but a vac leak would make it more pronounced.
Have you tried testing the intake under pressure?</strong><hr></blockquote>
I have yet to test the intake under pressure. That is a good idea. I've heard of people capping the exhaust as well to test the entire engine for leaks. I may try to do that.
What effect would a vaccum/boost leak have under full boost, 14-15psi, WOT, 3rd gear, 5000 rpms. It seems like if these conditions are present, especially the 14-15psi boost, a vaccum leak would have virtually no effect. The tps sees WOT, the afm should be open, the klr sees 14-15 psi, and there is 14-15 psi in the intake manifold. I did replace all the rubber hoses and boots under the hood.
I haven't checked for dme error codes, but I think I will do that as well.
One other thing, the control for the charcoal canister is not hooked up at all, the throttle body fitting is plugged, and the turbo intlet tube (Porsche calls it an airbox) has the fuel vapor hole plugged. Not sure if this would have any effect upon fuel delivery.
[quote]Originally posted by Toolmaster:
<strong>I feel your pain...</strong><hr></blockquote>
I feel dirty when I drive it hard.
[quote]Originally posted by Toolmaster:
<strong>Sounds to me like it's a vacuum leak. I know it sounds funny, but only under high load (high pressures in the intake) do you see the problem...
The lean condition on 4 is almost normal on these cars, but a vac leak would make it more pronounced.
Have you tried testing the intake under pressure?</strong><hr></blockquote>
I have yet to test the intake under pressure. That is a good idea. I've heard of people capping the exhaust as well to test the entire engine for leaks. I may try to do that.
What effect would a vaccum/boost leak have under full boost, 14-15psi, WOT, 3rd gear, 5000 rpms. It seems like if these conditions are present, especially the 14-15psi boost, a vaccum leak would have virtually no effect. The tps sees WOT, the afm should be open, the klr sees 14-15 psi, and there is 14-15 psi in the intake manifold. I did replace all the rubber hoses and boots under the hood.
I haven't checked for dme error codes, but I think I will do that as well.
One other thing, the control for the charcoal canister is not hooked up at all, the throttle body fitting is plugged, and the turbo intlet tube (Porsche calls it an airbox) has the fuel vapor hole plugged. Not sure if this would have any effect upon fuel delivery.
06-27-2002, 04:02 PM
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Another thing I was thinking is that one of the inector drivers in the dme was on the fritz, causing one of the injectors to intermittently not operate under high duty cycles.
Just another theory.
Just another theory.
06-27-2002, 05:10 PM
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[quote]Originally posted by superjet.1:
<strong>sounds like a boost vacuum leak check your couplers on your pipes and throttle body.they may seem tight to the touch but under 15 pounds of boost a good leak can occure.</strong><hr></blockquote>
Oh yeah... vaccum/manifold pressure controls the fuel pressure regulator and the fuel damper. I'll have to scratch what I was saying above about the vaccum lines not having much to do with this.
<img src="graemlins/c.gif" border="0" alt="[ouch]" /> <img src="graemlins/c.gif" border="0" alt="[ouch]" /> <img src="graemlins/c.gif" border="0" alt="[ouch]" />
<strong>sounds like a boost vacuum leak check your couplers on your pipes and throttle body.they may seem tight to the touch but under 15 pounds of boost a good leak can occure.</strong><hr></blockquote>
Oh yeah... vaccum/manifold pressure controls the fuel pressure regulator and the fuel damper. I'll have to scratch what I was saying above about the vaccum lines not having much to do with this.
<img src="graemlins/c.gif" border="0" alt="[ouch]" /> <img src="graemlins/c.gif" border="0" alt="[ouch]" /> <img src="graemlins/c.gif" border="0" alt="[ouch]" />
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06-28-2002, 10:42 AM
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Steve -
In a stock car, ANY leak after the Air Flow Meter will have icky effects.
Even with a little air being blown out, the car would be injecting fuel for the metered air that entered the intake... Meaning that you could be injecting more fuel than you should be.
Now - couple that with the potential for the leak to be near the FPR, meaning the FPR would potentially see less boost, meaning it's pressure wouldn't RAISE as much, meaning a net result of not enough fuel...
Really depends on where the leak is - if there is one. The J-boot is notorious for leaking... Pressure in the intake from a compressor is the BEST way I've found to secure every leak.
If you stuff a rag in the exhaust (wet the rag first) then you can check the exhaust side for leaks too, without worrying about blowing seals bu having the exhaust totally blocked off.
HTH!
In a stock car, ANY leak after the Air Flow Meter will have icky effects.
Even with a little air being blown out, the car would be injecting fuel for the metered air that entered the intake... Meaning that you could be injecting more fuel than you should be.
Now - couple that with the potential for the leak to be near the FPR, meaning the FPR would potentially see less boost, meaning it's pressure wouldn't RAISE as much, meaning a net result of not enough fuel...
Really depends on where the leak is - if there is one. The J-boot is notorious for leaking... Pressure in the intake from a compressor is the BEST way I've found to secure every leak.
If you stuff a rag in the exhaust (wet the rag first) then you can check the exhaust side for leaks too, without worrying about blowing seals bu having the exhaust totally blocked off.
HTH!
06-28-2002, 01:26 PM
#9
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Steve, I have experienced similar conditions to what you have described. When I put full throttle in and the boost came up I would get stumbling or rough running and not the smooth solid pull to redline that is normal. In my case I could adjust the load mixture with the mixture controller to experiment a bit. For my car a slight increase to the rich side made the condition worse and a slight decrease toward lean smoothed things out. I was still staying acceptably rich on the afr meter.
If you have a adjustable fuel pressure regulator try lowering the fuel pressure a few psi at a time and see how it runs. I would concur with others to make sure there are no leaks anywhere first.
Dan
If you have a adjustable fuel pressure regulator try lowering the fuel pressure a few psi at a time and see how it runs. I would concur with others to make sure there are no leaks anywhere first.
Dan
07-01-2002, 06:16 PM
#10
Race Director
"one of the inector drivers in the dme was on the fritz, causing one of the injectors to intermittently not operate under high duty cycles."
There's only one injector driver in the DME. It's split into a pair of grounds that drive two injectors apiece, but at the very bottom hardware level, there's only one driver.
I suspect a leak in your intake somewhere as well. Perhaps a small one somewhere that doesn't show up unless you have sufficient boost-pressure to open it up. Check all the hose-clamps from the turbo outlet onwards.
There's only one injector driver in the DME. It's split into a pair of grounds that drive two injectors apiece, but at the very bottom hardware level, there's only one driver.
I suspect a leak in your intake somewhere as well. Perhaps a small one somewhere that doesn't show up unless you have sufficient boost-pressure to open it up. Check all the hose-clamps from the turbo outlet onwards.
07-02-2002, 02:02 AM
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Sounds like everyone pretty much agrees on this. I did inspect the vaccum lines for the fuel system and all appeared well.
I inspected the various intake boots a while ago and couldn't find any issues. I guess I will take a closer look at them tomorrow evening.
I inspected the various intake boots a while ago and couldn't find any issues. I guess I will take a closer look at them tomorrow evening.
07-03-2002, 03:57 AM
#12
Race Director
Here's another way to test for a vacuum/boost leak. If you have an air-fuel ratio gauge, see what happens when the stumbling occurs. It should spike up to the rich side since that metered air is escaping, yet the injectors are still dumping in what the DME thinks is the correct amount of fuel.
On my car, I found a 1/2" slit on the bottom side of the hose between the turbo outlet and the intercooler pipe. It would seal fine until boost hits 13-14psi and it would let go, causing the stumbling.
On my car, I found a 1/2" slit on the bottom side of the hose between the turbo outlet and the intercooler pipe. It would seal fine until boost hits 13-14psi and it would let go, causing the stumbling.
07-07-2002, 01:23 PM
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Yesterday I removed the boost tubes, air intake, J-boot and checked everything very closely for any potential leaks. I replaced all the intercooler boots and the j-boot 10,000 miles ago and they still appear to be in very good condition. The j-boot was tight, but not as tight as it should have been at the turbo. Also, the throttle body boot had some signs of blowing, but I suspect this was from the single time it dramatically blew on the dyno back in February and not a recent issue. I also checked over the vaccum lines and they looked good and were hooked up correctly. I replaced the small vaccum tubing, but not the boots 10,000 miles ago.
The problem still exists without any change.
I'd love to do the leak test, but I am currently 1,000 miles away from my tools and a private garage. I am currently stuck with the ghetto solution of doing work in the parking garage of a Kragen with a few basic tools.
I plan to order a new throttle body boot and some silicone line for the vaccum hoses this next week.
Something that has me concerned is my lack of a venturi tube. When I replaced my intake hoses, I removed the venturi tube and instead hooked one of the holes on the intake manifold directly to the brake booster and the other hole directly to the idle air controller, consistent with the setup on '88 and newer turbos. Today I plan to find some caps to cover the two holes on the intake manifold and a plug to cover the iac hose. I'll see if this makes a difference. I'll also be cautious of the unassisted brakes!!!
I am also going to try removing my lbe, though since I don't have a jetted banjo bolt this may introduce other issues since my chips are designed for 15 psi.
Finally, I will print out the procedures for pulling dme error codes and see if there are any issues.
The car has a stock '86 fpr and I don't have an a/f meter.
Thanks for the help, and I will keep you posted.
The problem still exists without any change.
I'd love to do the leak test, but I am currently 1,000 miles away from my tools and a private garage. I am currently stuck with the ghetto solution of doing work in the parking garage of a Kragen with a few basic tools.
I plan to order a new throttle body boot and some silicone line for the vaccum hoses this next week.
Something that has me concerned is my lack of a venturi tube. When I replaced my intake hoses, I removed the venturi tube and instead hooked one of the holes on the intake manifold directly to the brake booster and the other hole directly to the idle air controller, consistent with the setup on '88 and newer turbos. Today I plan to find some caps to cover the two holes on the intake manifold and a plug to cover the iac hose. I'll see if this makes a difference. I'll also be cautious of the unassisted brakes!!!
I am also going to try removing my lbe, though since I don't have a jetted banjo bolt this may introduce other issues since my chips are designed for 15 psi.
Finally, I will print out the procedures for pulling dme error codes and see if there are any issues.
The car has a stock '86 fpr and I don't have an a/f meter.
Thanks for the help, and I will keep you posted.
07-22-2002, 04:36 PM
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The problem seems to be solved. The other night, I was experiencing this problem and was able to see smoke in my rearview mirror through the headlights of the car behind me. Of course, this just confirmed my intermittent rich condition.
Anyways, this made me decide to replace the fuel pressure regulator and fuel dampener with new stock items. After driving it 70 miles yesterday evening, I can confidently say that my problem is gone.
Anyways, this made me decide to replace the fuel pressure regulator and fuel dampener with new stock items. After driving it 70 miles yesterday evening, I can confidently say that my problem is gone.
07-24-2002, 12:40 PM
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Steve I sorry I didn't read this earlier. If you look in the archives you will find me complaining about a "bucking and surging" very similar to what you describe. In my instance it turned out to be a failing fuel pressure dampener.
