You'll have to record the run and play it back unless you have someone with you with a real sharp eye. The TPS, as you know, will start out about .42 volts and theoretically climb until it hits about 4.8 volts, in a linear fashion. In my case, the voltage dropped to 0 in one frame, then went right back up to the 4 volt region in the next frame. The backfire occured at 0 volts. I wouldn't floor the pedal all the way until you figure it out, as I'm sure the back fire can't be helping things. Let us know what you find out.
Backfire under wot and lost idle
- Thread starter Timbuick
- Start date
You'll have to record the run and play it back unless you have someone with you with a real sharp eye. The TPS, as you know, will start out about .42 volts and theoretically climb until it hits about 4.8 volts, in a linear fashion. In my case, the voltage dropped to 0 in one frame, then went right back up to the 4 volt region in the next frame. The backfire occured at 0 volts. I wouldn't floor the pedal all the way until you figure it out, as I'm sure the back fire can't be helping things. Let us know what you find out.
Thanks Rick, that make sense. I'll take drive out with a friend and ease into the throttle and see what the scantool is reading.
When I reported a backfire I may not have described it correctly. Essentially under hard throttle its as if someone has pulled a plug and the car dives and then recovers However, it is always under the same conditions, not random.
When I reported a backfire I may not have described it correctly. Essentially under hard throttle its as if someone has pulled a plug and the car dives and then recovers However, it is always under the same conditions, not random.
Do you have another set of sparkplugs?
Had a problem with a broken ceramic insulator around the center electrode once, i would pull the plug out and hold it straight up and it looked normal but when turned upside down as when installed in the head the insulator would slide down on the electrode and eliminate the air gap.
Had a problem with a broken ceramic insulator around the center electrode once, i would pull the plug out and hold it straight up and it looked normal but when turned upside down as when installed in the head the insulator would slide down on the electrode and eliminate the air gap.
OK guys, latest update;
checked resistance on the HT leads=no problems
plugs all gapped and good
checked TPS and had wife tap it while I checked the scanmaster=no problems.
Drove the car out whilst watching the TPS numbers. Got to 85mph in progressive throttle and TPS never showed more than around 2 volts. Sould it read higher.
Car started to break down under sustained throttle. All I have not checked or replaced is the Crank and cam senors.
Any ideas, i'm ready to park it up and forget about it
checked resistance on the HT leads=no problems
plugs all gapped and good
checked TPS and had wife tap it while I checked the scanmaster=no problems.
Drove the car out whilst watching the TPS numbers. Got to 85mph in progressive throttle and TPS never showed more than around 2 volts. Sould it read higher.
Car started to break down under sustained throttle. All I have not checked or replaced is the Crank and cam senors.
Any ideas, i'm ready to park it up and forget about it
OK guys, latest update;
checked resistance on the HT leads=no problems
plugs all gapped and good
checked TPS and had wife tap it while I checked the scanmaster=no problems.
Drove the car out whilst watching the TPS numbers. Got to 85mph in progressive throttle and TPS never showed more than around 2 volts. Sould it read higher.
Car started to break down under sustained throttle. All I have not checked or replaced is the Crank and cam senors.
Any ideas, i'm ready to park it up and forget about it
If you accelerate gradually, I don't think the TPS will get into the 4 volt range, if that is what you were expecting. You really need to goose the pedal to get up to 4. So 2 volts might be correct, given the way you gradually accelerated. If it stayed at 2 or below when you wife tapped it, then I think she needs to tap it harder. What you want to do is check the TPS voltage when the car starts to break up. Did the TPS volts continue to increase as you accelerated? If you take your foot off the gas, TPS will drop, so we want to see if it is climbing as it should. Don't give up, we've all been through this before.
Thanks Rick,
The TPS rose and fell in line with the acceleration/de-acceleration. I tapped the TPS around and tried to see if it moved whilst my wife monitored the scanmaster. No problems with that.
What is dificult is that for the health of the motor I dont want to get into full throttle and cause a back fire, but on the other hand if i dont I cant guage the TPS figures
I can now drive the car and predict when it will start to break down, if it were a Holley carb on my old muscle car I would suspect fuel starvation or vac leak.
Very tricky.
The TPS rose and fell in line with the acceleration/de-acceleration. I tapped the TPS around and tried to see if it moved whilst my wife monitored the scanmaster. No problems with that.
What is dificult is that for the health of the motor I dont want to get into full throttle and cause a back fire, but on the other hand if i dont I cant guage the TPS figures
I can now drive the car and predict when it will start to break down, if it were a Holley carb on my old muscle car I would suspect fuel starvation or vac leak.
Very tricky.
Well, a new TPS sensor is around $45 here I believe. I'm not sure that's what you need, and being an electrical part, you probably can't return it if that is not the problem. But I've wasted more than that on other things. Do they sell parts for the GN in the UK?
ELLISDALLASWE4
Member
- Joined
- Nov 7, 2005
Questions that could help us help you. Do you have a fuel pressure guage that you can see while you are driving? Can you at any time smell gas anytime in the car when you go WOT? Does the car do any kind multi-pop or is it more of a boom. Did you double check all vacuum lines and do you have a vacuum gauge. The vacuum diagram is on the pass side around the fan box. What is the static setting on the fuel reg? What is it at WOT? You looking for ANY leak as it will effect the boost gauge and/or the fuel reg. If you are static at 43 and you go to 15 lbs boost the that pressure needs to be very close to 58 not something like 51...
David Ellis
Dallas
David Ellis
Dallas
I have a FP guage in the car and it does show pressure rising in line with boost. I dont have a vacuum guage to check. Can't smell gas and the FP stays put when i leave the car with the ignition on/engine off.
When the car defaults it spits and just nose dives , I lift of throttle and perfect again!
When i had one of the up pipe hoses blow by it was different in that i could feel the power drop off and easily rectify it by correct fitment of the hose.
This current problem fels like a plug ahs been pulled as i've mentioned. So far, nothing has fixed it. I replaced the cam sensor cap today, but haven't yet driven it.
When the car defaults it spits and just nose dives , I lift of throttle and perfect again!
When i had one of the up pipe hoses blow by it was different in that i could feel the power drop off and easily rectify it by correct fitment of the hose.
This current problem fels like a plug ahs been pulled as i've mentioned. So far, nothing has fixed it. I replaced the cam sensor cap today, but haven't yet driven it.
i'm on the verge of giving up with this car. I cannot fix this problem Changed cam sensor cap. No change. checked the ohms on the coilpack, all good.
I have not yet done a compression check, but would a blown head gasket cause the car to breakdown under boost at 10psi+?
Otherwise, car drives, starts,idles perfectly, but still breaking down under sustained throttle
I have not yet done a compression check, but would a blown head gasket cause the car to breakdown under boost at 10psi+?
Otherwise, car drives, starts,idles perfectly, but still breaking down under sustained throttle
Kind of sounds like fuel pump to me. The pump works up to a certain point, then fails, you let off gas and all is good until you accelerate to that point again, at which time the pump fails again. No good mechanics near you that good diagnose a bad fuel pump?
Rick, I'm prone to agree with you and I still have an old pump in my bits box. I may just change it over to at least check it. My FP guage does show pressure rising in line with boost. Even so, can I check my pump via a volt meter or is it a case of somehow checking actual delivery flow?
bmackinnon
Active Member
- Joined
- Feb 24, 2005
Are you watching the FP when the car takes a nose dive? A failing pump will build pressure with boost up to a point, and sometimes be just fine in 1st/2nd gear, but when you really put a high volume demand on the pump (ie. 3rd gear, wot, full boost), the pump can't keep up and the pressure plummets.... let off, start building boost again, pressure goes up again, until it can't keep up again....
It really sounds like the fuel pump is dying... need to have the girlfriend keep an eagle eye on the FP while you go for a drive and see what's going on... roll into it hard in 3rd gear and see what happens... really no other way to check it..... unless you have a fuel pump flowbench/dyno...
If the fuel press. is keeping up and not the issue, the most logical other thing is the coil pack or ign. module.... I know, I know... you swapped the CP.... but are you SURE your spare was good? Do the ohm test on 'em.... should be 11-13k front to rear for each pair.... better if you can ohm 'em hot, after a drive... if it's not the pump, or the coilpack, it almost has to be the module... or so one would think....
bmackinnon
Active Member
- Joined
- Feb 24, 2005
He swapped the coilpack with a spare.... but not the module from what I can tell....
bmackinnon
Active Member
- Joined
- Feb 24, 2005
Send me your coilpack and I will test it with my Caspers Coilpack Tester. You will know for sure and can rule that out. I only charge $500 for this test.
PM me for address details.
Ed
Might be a fairly timely/pricey process.... shipping from the U.K./England to Looziana might be a killer!!
Betting swap parts are fairly hard to come by there also....bmackinnon
Active Member
- Joined
- Feb 24, 2005
They are bolted together, but 2 seperate components and can be replaced/serviced as such... and usually are... :wink:
