tmking66

Been trying to get the car to go over the 3800 hump. This has not been the hesitation but total inability to rev past 3800 while driving. Goes past 3800 easy when in neutral. Anyhow, here is the setup. This is an s5 with the emissions removed in a s4 car. After reading many posts about these problems I began to realize that this was not a grounding problem, the engine is well grounded. Most other peoples problems seem to have come from some of the emissions equipment that this engine does not have. One thing that was still hooked up on my car though was the boost sensor over on the passenger side in front of the strut. Reading the Haynes manual about testing secondary injectors (which is why it will not go over 3800 rpms while driving is that the secondarys are not coming on) it said to disconnect the vac. hose on the bost sensor to see if the sec. inj. are working. I did this and then blocked off the vac. hose so there would not be a leak. Took the car for a test drive with the boost sensor disconnected and vac. line blocked off and TA DA! Revs up to redline quick with plenty of power. Now, question is, is it OK to operate the engine with this setup. What exactly does the boost sensor do?

WAYNE88N/A

That's really weird- have you been getting boost sensor codes? The ECU uses the combination of the tach signal and intake (vac, boost) pressures (and maybe other inputs, I'm not sure) to determine when to kick in the secondaries. I know with my setup (5/6 ports open at 3,000), the boost sensor won't let the secondaries kick in 'till much later than usual (4,500 or so). As far as disconnecting the boost sensor causing problems, all I know is that the ECU will use a stored "fail-safe" signal in place of the boost sensor numbers. Let us know (if you're gonna leave it disconnected) if you have issues (gas mileage worse, etc...)

tmking66

Yeah, the gas milage issue is something that I want to watch over the next couple of days. I'm thinking that maybe the secondaries are operating all the time right now. But if that was the case would it not have an effect on the idle speed which has not changed?

WAYNE88N/A

they still should come on at the 3800 tach signal- that's exactly what that test proves...I'm thinking driveability issues MIGHT happen, but I've never done it (disconnect the sensor) for any length of time, so I dunno...NZ might know- he knows EVERYTHING

mwpayne

Interesting..my s4 vert hesitates bad at 3800..I think I'll try that tomorrow!

cloead

To my knowledge.. disconnecting the pressure sensor causes the secondaries to come on at 3800rpm regardless of throttle input. Normally they only fire above 3800rpm if you are on the pedal pretty hard.. but without the pressure sensor the come on regardless.

J-Rat

iTrader: (2)

Bingo

tmking66

quote:
--------------------------------------------------------------------------------
Originally posted by cloead
To my knowledge.. disconnecting the pressure sensor causes the secondaries to come on at 3800rpm regardless of throttle input. Normally they only fire above 3800rpm if you are on the pedal pretty hard.. but without the pressure sensor the come on regardless.



If this is the case, (secondaries come on at 3800rpms regardless of throttle input)) then my problem is solved. If the car is being reved much past 3800 I'm getting on it pretty hard anyway. I will post back here after driving a little more and let you know how things work out.

RETed

You're going about a very dangerous way of solving a problem with is probably a band aid fix.

You're trying to solve the first problem by introducing a solution that can eventually lead to you killing your engine.

I dunno where your logic stems from, but we've researched this 3800RPM hesitation problem pretty thoroughly, and my write-up points to that.
http://fc3spro.com/TECH/FAQ/3800.html


-Ted

tmking66

Ted, first off my engine is grounded extremely well. Grounding is not a problem. Dirty injectors are not the problem. These are the only two solutions offered by the article you provided the link for. There is something else causing the ECU to not actuate the secondary injectors. Please explain HOW that disconnecting the vac. line to the boost sensor can kill an engine. My logic on this is that the Haynes manual says to disconnect the vac. line to the boost sensor to check operation of the secondary injectors. As I said in my original post here ALL emissions equipment has been removed from this engine. Not sure but I am thinking that some of this equipment may have sent signals to the ecu to activate the secondaries. With the emissions equiment gone there is nothing there to send the signal so the secondaries NEVER come on. My problem was actually not a hesitation but a REFUSAL to rev. over 3800. No amount of throttle would get the engine past 3800. It was like hitting a wall. With the boost sensor disconnected the car runs GREAT. Revs smoothly up to redline and idles well at about 800 rpms and is nowhere close to getting too hot (temp. gauge reading at about 1/3 up the gauge). Gas milage has not significantly been affected. It has gone down some but that is most likely because I have been running the car a lot harder since getting the secondaries working. PLEASE explain how not having the boost sensor connected is dangerous to the engine. If you can make any other recommendations as to how to fix the problem while keeping this sensor connected I would love to know. Also, this is not a turbo car so it is not being boosted by a turbo charger so overboost cannot be a problem. What else could kill my engine? It is not overheating, it is getting all the required lubrication, it is not being overboosted, timing is right on the mark, what else is there?

RETed

You need to search for the answer.
The answer is all over this forum.

-Ted

tmking66

Oh that is just wonderful advice Ted. Search for the answer it is all over the board. Wow, what words of wisdom. I never would have thought about doing that. Search for the answer, man you should start a consulting business. With answers like that you could solve everybody's problems I bet.

You know, I asked an honest question AFTER DOING A LOT OF SEARCHING. If you really knew the answer I think you would have posted something besides

(You need to search for the answer.
The answer is all over this forum.

-Ted)

I know if I knew the answer to someones question I would answer it no matter how many times it had been asked. But that is just me I try to be a nice guy when people let me .

Anyone else have any USEFUL input.

J-Rat

iTrader: (2)

Swapped the ECU yet?

tmking66

No, I have not swapped out the ECU. I was hoping to avoid that if possible. Again I am wondering if the setup I have now is OK. The car is running great with the boost sensor disconnected.

mwpayne

Well, it sucked for my S4 vert..wouldn't even hold an idle with the boost sensor unhooked and vac line plugged. Guess I'll live with the hesitation for another week or so, then Landers installs my TII engine!!

tmking66

Worth a try for you I guess. Again though mine is a s5 engine with all emissions equipment removed. Good luck on the TII conversion. I would love to have a TII convertable.

mwpayne

Oh, I appreciate the suggestion and glad it worked for you, guess the S4 setup is different. Did you ever find out if keeping it unhooked would ever be detrimental to the engine?
And, yes, I'm excited about the vert conversion, I'm 44 and never owned a vert till last month, current engine is weak but that will soon be history. Kevin's got me now searching for things like guages, a downpipe, a TII hood, etc.
Best of luck to ya