Strange misfire, HELP ASAP

Budfreak · #1 03-18-2007, 10:44 PM

I just got done putting a motor with fresh water pump, thermostat, idlers, all belts, plugs, and so on plus 4.44's into Wannarace928's SVX. It seems to run perfectly fine when first started and allowed to idle and it will rev up fine in "P" if you don't go over 3,500 RPM's. If you do go over 3,500 RPM's, When you let off the accelerator it will start missing a cylinder and either stall or nearly stall. It will then miss and idle rough for about 15 seconds and then the cylinder starts firing again and it runs perfect. When driving say 55 MPH, It will not accelerate when you floor the pedal, It just drops into second and revs. You have to slowly press the pedal down and keep it in 4th gear to accelerate. Also, When in "P" it will only rev to 5250 RPM's maximum. I checked the codes and got a code 31, So I changed the TPS and the code went away and there are now no codes.

Any ideas?

I'm leaning towards a coil right now and I plan to swap all 6 first thing in the morning and see what happens.

92svx95 · #2 03-19-2007, 12:56 AM

If you test the coil plugs with a metal object(screwdriver) at night or in a garage with the lights off then you can for sure find out if a coil is bad. It's ok to use a flashligh

Trevor · #3 03-19-2007, 03:02 AM

It is presumed that you correctly set the TPS with a voltmeter when you installed a replacement. If not check for advice in the "how Too" section.

Edit P.S. Sorry I did not take notice that you are a member with in depth experience.

Budfreak · #4 03-19-2007, 07:00 AM

Quote:

Originally Posted by Trevor

It is presumed that you correctly set the TPS with a voltmeter when you installed a replacement. If not check for advice in the "how Too" section.

Edit P.S. Sorry I did not take notice that you are a member with in depth experience.

Yes Trevor, I swapped out the TPS and set it to .50 Volts and I also swapped the MAF. It seems this problem as happening when she brought it to me, So now I'm looking into the computer and fuel pump.

TomsSVX · #5 03-19-2007, 09:01 AM

also, if you can get it to miss consistantly, unplug the injectors to find the mystery cilinder. Sounds like the same problem I am having with my teal and I still need to change my fuel pump. It pretty common as many people are talking about it. I changed all my injectors and my fpr and still nothing. Changed the MAF and reset my TPS. I really think it is just and overpressurization of the fuel system and could be caused by something in the tank... presuably the fuel pump. I bet if you disconnect the fuel lines and let the system purge, it will run well for a little while then begin the start acting up when the fuel pressure gets too high again. Good luck

Tom

Budfreak · #6 03-19-2007, 02:06 PM

Quote:

Originally Posted by TomsSVX

also, if you can get it to miss consistantly, unplug the injectors to find the mystery cilinder. Sounds like the same problem I am having with my teal and I still need to change my fuel pump. It pretty common as many people are talking about it. I changed all my injectors and my fpr and still nothing. Changed the MAF and reset my TPS. I really think it is just and overpressurization of the fuel system and could be caused by something in the tank... presuably the fuel pump. I bet if you disconnect the fuel lines and let the system purge, it will run well for a little while then begin the start acting up when the fuel pressure gets too high again. Good luck

Tom

That's exactly what I'm thinking also. I ran a fuel pressure check and it is at over 60 PSI when running on the return line with the regulator hooked up. This motor was just put in and the old motor was doing the same thing, So I too am leaning towards changing the fuel pump. I'm thinking it has too much pressure and is running so rich that when I rev it above 3,500 RPM it fouls the plugs temporarily and causes the miss. It is even worse when cold I found out. When I rev above 3,500 with the engine cool it will immediately stall and simply refuses to start again without the gas halfway to the floor.

wannarace928 · #7 03-19-2007, 02:17 PM

Quote:

Originally Posted by Budfreak

When I rev above 3,500 with the engine cool it will immediately stall and simply refuses to start again without the gas halfway to the floor.

Now it was doing something very similar to that for me before I brought it to you, some mornings I would have to hold the pedal ALL the way to the floor and hold it there for a short while even after the car started because the RPM's would be down at 0 and it would sputter sputter sputter until it got a little warmer then the rpm's would suddenly REV and then I could slowly let off the gas pedal until the rpm's evened out. If I didnt slowly let off the gas it would instantly die then good luck starting it.

Budfreak · #8 03-19-2007, 10:01 PM

Ok, so far I've replaced the following:
MAF
igniter
fuel filter
fuel pump
ECU
TPS

I've checked for vacuum leaks and so on but haven't found anything out of the ordinary. The ECU is throwing no codes. I installed new idlers and a timing belt and I know the timing is right as I tripled checked, plus it runs great until it gets to about 3,500-4,000 RPM's. Runs very very quiet and smooth when idling. I can't think of anything else to replace that would be causing this problem as it was happening before I swapped the motor and tranny meaning it is not any sensors located on the motor and has to be something electronic or fuel related located elsewhere. But what?????

I'm lost on this and tired of swapping parts. Anybody have a select monitior for sale?

Trevor · #9 03-19-2007, 10:55 PM

Curly one.

Trying to jog your thoughts. --- Take into account any and every item you may have transferred from the original motor. You have probably done so but as said, a memory jog.

Budfreak · #10 03-19-2007, 11:02 PM

Quote:

Originally Posted by Trevor

Curly one.

Trying to jog your thoughts. --- Take into account any and every item you may have transferred from the original motor. You have probably done so but as said, a memory jog.

The only things transferred were the accessories and a few vacuum lines that had been cut on the new motor and were swapped from the old one. The motor came with it's own coils and sensors ready to run except for the accessories.

Trevor · #11 03-19-2007, 11:48 PM

Quote:

Originally Posted by Budfreak

The only things transferred were the accessories and a few vacuum lines that had been cut on the new motor and were swapped from the old one. The motor came with it's own coils and sensors ready to run except for the accessories.

This may or may not help, and will certainly not make you happy.

As a fact I have found in the electronics arena, that what one would think very, very, very unlikely can occur.

In other words the two motors may have had a similar sort of problem.

I think that right or wrong you must consider coils plugs, boots and HT leaks.
Please be sure I am trying to help and don't get mad, if you do not have success, as a result of my meddling.

P.S. Electrickery has often driven me mad.

Nothing permanent mind you.

Nomake Wan · #12 03-20-2007, 07:09 AM

Probably totally off-base on this one... but has the ECU been reset since you swapped motors? Maybe it's just not reading one of the sensors correctly...

GOT2HAVESVX · #13 03-20-2007, 09:01 AM

Quote:

Originally Posted by Nomake Wan

Probably totally off-base on this one... but has the ECU been reset since you swapped motors? Maybe it's just not reading one of the sensors correctly...

Its on his list as being replaced. Does it still need resetting?

TomsSVX · #14 03-20-2007, 09:22 AM

Quote:

Originally Posted by Trevor

P.S. Electrickery has often driven me mad.

Nothing permanent mind you.

Whatever you say Trevor....

Tom

Budfreak · #15 03-20-2007, 09:43 AM

Quote:

Originally Posted by Trevor

This may or may not help, and will certainly not make you happy.

As a fact I have found in the electronics arena, that what one would think very, very, very unlikely can occur.

In other words the two motors may have had a similar sort of problem.

I think that right or wrong you must consider coils plugs, boots and HT leaks.
Please be sure I am trying to help and don't get mad, if you do not have success, as a result of my meddling.

P.S. Electrickery has often driven me mad.

Nothing permanent mind you.

Yes, I thought of that also, But didn't have the time or energy to swap the coil packs and the miss isn't consistent long enough to trace. I always appreciate your advice Trevor, Your a smart man and a great value to this community. I'm taking the car back to her today and she has a friend who can hook it up to diagnostics and find the exact problem possibly and then I can go right to it and fix it. It also decided to start a small leak yeterday out of the brand new rear main seal, Just as a little bonus for me I guess.

The second I find a select monitor consider it sold. What a value it would have been on this one.