Paxton bogging / cutting out at 2500 - 3000 rpm

[Viper X]

Car runs fine for about 20 - 25 minutes after cold start, then acts like it's running out of fuel at 2500 - 3000 rpm under wot and bogs. Runs fine at light throttle.

Thought it was a bad fuel / water in the fuel problem. Ran two tanks through the car with fuel injector cleaner - no help.

Changed the fuel filter. Ugh! You don't want to do this. Have to pull the belly pan, exhaust crossovers and then reach way up in there to get to the thing. After all of that, the fuel filter was fine, replaced it anyway but still no help - still have problem.

Checked the auxiliary fuel pumps. Tightened all connections. Used a meter to check that they were both receiving current. Both firing progressively - no help.

Belt is tight. Supercharger is still spinning.

I'll check fuel pressure / boost tomorrow but now suspect computer issue, perhaps with the Paxton supplied Timing controller.

Will call Paxton's tech support tomorrow.

Anyone else have this or anything like this happen yet?

Dan

 

[DB/Paxton SRT-10]

Dan:

Sorry to hear about your problem. I would suspect that one of the auxilliary fuel pumps has malfunctioned (despite the presence of current at the pump). That would account fot the car running fine at at light load when fuel demand is low. I would expect that if the ECM was malfunctioning, the car would probably not run. This is the first Gen III Paxton problem that I have seen reported. Good luck. Keep us posted.

Darel

 

[Viper X]

Thanks Darel,

Any idea of the best "in line", underhood fuel pressure gage? Where to get, etc.

 

[GR8_ASP]

I am going to take a wild guess and say the vacuum/boost hose to the Split Second unit is leaking, pinched off or something like that. Without the boost signal it will not add fuel pressure or take out timing. That would be lean enough to cause lean misfire. Another possibility would be a poor ground connection somewhere.

If you are running the stock Paxton fuel system the fuel pumps have good voltage and ground as they will stop fuel flow if one is not working at all times.

BTW I run a fuel pressure gauge all the time as it instantly tells of a fuel pressure issue. It jumps to about 80 psi when near boost and near 100 as it get to high boost (the initial increase is the pump coming on and the increase after that is the Paxton fuel control unit - also boost driven). You do not have to watch it closely as the quick needle movement provides assurance. I have a a/f gauge but find that it does not help when driving as the reading is somewhat erratic with a small delay.

 

[Cris]

Another thought. Check and make sure you can hear the intercooler water pump. If you do not you may have a controller or electrical issue.

 

[Viper X]

Thanks guys,

Cris, intercooler pump working normally. Mine is easy to hear.

GR8 ASP, checked all the under hood ground wires and re-worked / re-secured them today. Tested continuity and it was all good. Vacuum is a steady 15 at idle, so maybe a small leak. I'll check the vacuum line into the control unit next. Electrical power to the pumps is good, I checked it and I can feel them click or at least attempt to work.

Wonder why it works so well during warm up and stops working when warm?

No miss or detonation / pinging, just acts like it's running out of gas. Power goes down about 50% or more.

I will likely buy two new in line fuel pumps tomorrow. Who's fuel pressure gage do you run and where did you install it?

Thanks for the input.

Dan

 

[GR8_ASP]

When you go lean enough the engine misses a lot, but the tendency to detonate goes down. So it does sound like the fuel pump is not coming on some way (but just the second pump). You could switch pump wires to see if it is the second pump that has an issue (just the positive).

Do you get lots of pops and such from the exhaust? That is another side effect of excessively lean.

Regarding your vacuum signal, is your gauge and split second on the same circuit, or separate circuits? If the same, and the gauge is the furthest out then the gauge reading would indicate the lack of a leak. If not a leak could still be present and only affecting the branch the controller is on.

The only other connection I can collect is the hot vs cold. IN the first few minutes (maybe even 5 minutes during cooler days) the engine operates open loop and then goes to closed loop. In closed loop the a/f sensors try to keep the engine at or near stoich. If they have a problem in the measurement it could send a improper reading to the controller. This would only affect part throttle though as it goes to open loop as you approach WOT.

Back when I was having the cold start popping issue (during the transition from cold to hot) I tried just about everything to no avail. Two weeks ago I got a MIL for the RF O2 sensor. Once replaced the condition disappeared. That did cause a lean misfire as the O2 sensor was providing a faulty signal until fully warmed. Obviously not Paxton reklated but at the time I was getting concerned. To date my Paxton has been flawless (knock on wood) and I have over 5,000 miles of some pretty heavy use on it (including a track day).

 

[VIPER D]

gR8

You saved me a hole lot of typing. I am with you on every point you made. Its nice to see someone knows his viper as well as i do.

One thing i want to point out that an under the hood fuel pressure gauge is pretty useless you need to see it under boost!

vd..

 

[ViperGMC]

Being able to diagnose problems like that is why I installed a fuel mixture gauge and boost gauge in the cockpit. Losing a pump and going lean with boost can easily get the pistons hot and cast pistons can crack so watch the mixture closely. The system is an add-on so I don’t install it and forget, I watch it and check it. I have 20K miles and 20 some track days and the system is still running strong, very strong.

 

[GR8_ASP]

I agree with the gauges as I have a boost and fuel pressure gauge in my A pillar pod. I have not yet mounted the a/f gauge as it does not seem particularly useful in vehicle. The data logging aspect for tuning is of absolute necessity, but it has too much movement to be of use at WOT. I have little time to look at a gauge when in "hyper speed mode." Hard enough to watch the tach so I don't hit the rev limiter.

Like I mentioned the fuel pressure gauge indicates an increase in fuel pressure just before you hit 0 boost. That is really all you need to confirm as the rest is mechanical control (Paxton fuel control unit) and hopefully less prone to issues, though a broken boost line connection would impact it significantly. Come to think of that a 70 or 80 psi condition would probably be worse than 50 psi as it would have enough fuel to allow damaging detonation/preignition.

 

[Viper X]

Well, I isolated and tested the vacuum line going to the timing control last night, no leaks - held 20 inches for 5 minutes when I discontinued.

Car still runs fine - not fast - but fine at partial throttle. Cuts out almost completely at WOT above 3000 rpm. No misses, lean backfires, pinging, detonation, etc, just acts like it's running out of gas.

Spoke with Paxton today. Described symptoms and their recommendation was to replace both fuel pumps, at my expense of course, though they did discount them to me. They also said that if their computer had failed, the car would not run.

I have had electric in-line fuel pumps overheat and fail before, so this isn't that big of a surprise. I do think these things should have lasted longer than 8 months / 12,000 miles though, if they turn out to be the problem, and that's about all that is left.

The car runs great for about 20 to 25 minutes, just long enough for heat to build up in the engine compartment. I think I'll try to insulate the new fuel pumps somehow.

GR8 ASP, where did you get your A pillar pod gages? I saw Viper D's and liked them, but want them in English, not metric.

Thanks,

Dan

 

[ViperGMC]

Roe Racing has nice Mopar gauges. Got the pillar pod at Summit, don’t remember the part#, had to cut/grind to make it fit. I’ll shoots some pic’s tomorrow. I will have to disagree with GR8 on the A/F gauge. The A/Ff tells you the resultant of all that is going on in the engine. It is really the only way to see what is going through the engine. A fuel pressure gauge tells you if there is fuel before the intake, it does not tell you what is going into the engine. The A/F reads the exhaust and clearly tells you if everything is OK. Like I said, if you run lean with a SC you will burn a piston or two. It bounces around a lot sure, but if it reads lean for very long and I don’t ease off there will be big trouble. The first thing all the installers tell you after hooking up the SC is to get it on a dyno and check the fuel mixture to make sure the fuel delivery is happening properly.

 

[VIPER D]

I wouldn't even get on my monster w/o the wide band. That how serious i am about it.


vd..

 

[GR8_ASP]

I agree with the benefit of the a/f gauge, especially when dynoing/checking the system. I have a wideband controller installed, but only occasionally connect the gauge for a check. No place to install it and the wide needle swings made it the last gauge out. When I do have it in I need a 2nd person to watch it for a/f ratio when at WOT. Better to datalog and check it out on the computer later. Again, not as a check to see if things are operating properly. My assumption is that if I have the fuel pressure increase then I am increasing fuel delivery, and fuel pressure is a much easier driver observation.

My A pillar pod is for a Mustang (same one mentioned for a Gen I/II). Seems to work okay. I do plan on modifying it some this winter to rotate the gauges more toward the windshield.

 

[Viper X]

Problem solved, after a bunch of trial and error. Here's a recap:

1 - Changed fuel pumps to new. Car ran better for about 1 hour, then bogged again. Checked fuel pressure. 100 when cold under boost, 75 when warm. UGH!

2 - Pulled fuel control unit, checked and found small cylinder-shaped part in unit that controls fuel flow rough and sticky. Cleaned and reassembled. This thing is very touchy. Checked fuel pressure again, pegged gage almost immediately when revved (over 100 under boost when cold). Fuel pressure coming up much more quickly. 1:00 AM, tired, no time for a test drive and I'm sure my neighbors appreciated it.

3 - Thought about it all night. Got up early and did leak down vacuum test on only remaining vacuum line, the one to the race bypass valve (the valve you can hear letting off boost when you don't use it). Found a vacuum leak! Hooray! Removed valve from bottom of intercooler, disassembled and tested more thoroughly. Found that the nut at the bottom of the black cannister was loose on the stud! Added washer, re-installed nut, added another nut to lock the first nut. Tested and it held 25 inches of vacuum.

Re-assembled and car runs like a ***** ape again. Scared my wife. Didn't realize that this was probably going on for some time.

In closing, I've learned that all of the fuel control and management pieces used by Paxton rely on vacuum or boost. If you have a problem with your Paxton equipped car like this, it is likely boost or vacuum related. As a result of this problem, I added clamps or small zip ties to all vacuum lines.

Nice to have the beast back again. Now, where's that modded turbo Carera that I avoided last Saturday when my car was acting up .....

 

[slither]

Nice job ViperX, appreciate the write up in case problems arise for us Paxton users in the future. I installed clamps/zip ties on all my vacuum lines when I put in the system as well, so far no problems but this is really good info.

 

[DB/Paxton SRT-10]

Dan--
Congrats on your success.

Darel

 

[Qualitywires.com]

Something else to keep in mind to is the gap on the spark plug. Sounds like your problem was a simple fix. It's too bad Paxton basically told you you were on your own when you had some problems.

 

[Viper X]

Hey Darel,

Any chance you might make Crystal Cove this Saturday morning?

There may be a couple Vipers there, myself included.

Dan

 

[DB/Paxton SRT-10]

Dan,

Unfortunately, I am on-call this weekend at Hoag. Alas, I am still making payments on my Viper. Maybe the 12th?

Darel

 

[rleminv]

My Paxton is being installed by a qualified tuner as I type. My question is: Do you feel Paxton hung you out to dry? Was there any interest on their part to attempt helping you find or trace the problem? What does their Warrantee really mean and now that you solved the issue are you ok with Paxton's tech support?

Should I rethink my install?
Larry