ridiculous hesitation - MAP? O2? Gremlins?

[cjridert1]

ok - put an isc in b/c car was idling like crap = good. Put a new MAP sensor (soldered a 2.5 bar motorola MAP in) for my VPC = not good. I took the MAP signal wire voltage and got ~.45 at idle and my car was spewing out black liquid (fuel and accumulated carbon?) so I put the orig. vpc map in and we are back to the reason I was putting another one in in the first place.

When I go to step on gas (even light revs) the rpm's drop very low then climb @ normal speed - so there is a ridiculous hesitation (near stalling) going on. I figured it was the VPC's MAP sensor (signal voltage tested good @ idle (no boost), but wasnt tested @ anything else either as this would be a pain).

Also, probably related - in third gear pulls the O2 sensor is reading like .74V (LEAN!) so I figured it was the map sensor. Anyone have ANY idea what the problem could be? Thanks much!!!

 

[cjridert1]

anybody?

 

[cjridert1]

btw - new plugs, no boost leaks, base tim = 5btdc

 

[DSMopar]

how about your TPS? MAF can also cause these issues...

Whats your fuel pressure look like? Check when revving with vacuum plugged in...

 

[Matrixhunter]

Most likely as simple as a very big boost leak somwhere. Pressurize the car properly with a compressor and double check all your connections.

 

[cjridert1]

how about your TPS? MAF can also cause these issues...

Whats your fuel pressure look like? Check when revving with vacuum plugged in...

TPS is good, changed it about a month ago and is ~.9v closed. I have a nip-dens fuel pump and the fuel press. varies depending on what the engine is doing on the datalogger - is fuel pressure normally constant? If so, how do I change it so the pump puts out constant pressure? There is no MAF, just MAP.

Ill also check for a boost leak again later today

Thanks for the responses!!

 

[Matrixhunter]

without an adjustable fuel regulator you won't be able to change the pressure. Base pressure should be 37psi I believe on a 1g and 43 or so on a 2g. With load on the engine the fuel pressure is supposed to change.

 

[snowborder714]

is fuel pressure normally constant? If so, how do I change it so the pump puts out constant pressure?

As matrixhunter said, fuel pressure isn't constant. Base fuel pressure for a 2G is 43.5 psi. The only way to change this is with an AFPR (adjustable fuel pressure regulator). And your fuel pressure will change with a 1:1 ratio with boost. So if you're making 10 psi of boost, your fuel pressure will be 53.5 psi.

 

[cjridert1]

tested for boost leaks & didnt have any. Checked fuel pressure @ idle with datalogger (mmcd) and it told me ~11-12psi. Rev it and psi goes to ~60 then will dip down to 8 or so after you let off gas. How do I up the fuel pressure @ idle? Would that make sense why the car is having a bad hesitation?

Thanks for the responses

 

[1slo1g]

tested for boost leaks & didnt have any. Checked fuel pressure @ idle with datalogger (mmcd) and it told me ~11-12psi. Rev it and psi goes to ~60 then will dip down to 8 or so after you let off gas. How do I up the fuel pressure @ idle? Would that make sense why the car is having a bad hesitation?

Thanks for the responses

mmcd uses the ecu like the boost sensor it will NOT be accurate
get a gauge and hook it up

 

[cjridert1]

mmcd uses the ecu like the boost sensor it will NOT be accurate
get a gauge and hook it up

Will it will be close enough to accurate to assume the regulator is malfunctioning?

 

[1slo1g]

Me personally I would not trust it i would put a gauge inline you can get them cheap. http://www.erzperformance.com/ProductDetails.asp?ProductCode=WR21
This one is for 15 bucks cant go wrong.

 

[cjridert1]

Might as well put a afpr in? how necessary are they? I have a stock fpr in the mail and hope that fixes my problem but if it does - what are the benefits of running afpr (providing my base fp is about right)?

Thanks again!

 

[cjridert1]

If fuel pressure is only 11psi that means the pump is bad right? The stock fpr keeps pressure from being too high not too low right? So it isnt the fpr?

 

[snowborder714]

Might as well put a afpr in? how necessary are they? I have a stock fpr in the mail and hope that fixes my problem but if it does - what are the benefits of running afpr (providing my base fp is about right)?

Thanks again!

The stock FPR usually only gets overrun once you install a 255 pump. If you don't have one installed, I would say not worry about it.

If fuel pressure is only 11psi that means the pump is bad right? The stock fpr keeps pressure from being too high not too low right? So it isnt the fpr?

I could be the pump, but it could also be a clogged fuel filter (or even possibly a clog/kink somewhere else in the system). How are you testing your fuel pressure?

 

[cjridert1]

I could be the pump, but it could also be a clogged fuel filter (or even possibly a clog/kink somewhere else in the system). How are you testing your fuel pressure?

The filter is near new (4 months?) - I have a datalogger that I am using - I know its not as accurate as a mech. gauge, but it shouldnt be off by that much should it - would you believe the logger?

 

[snowborder714]

would you believe the logger?

No. Get a gauge and check it that way.

 

[cjridert1]

hooked a gauge up and it read a steady 37 or so, which means the pump isnt bad - too bad. Any other ideas why the car is hesitating? I feel it may be vpc related (since mas was removed) - thoughts? (No I dont have stock mas laying around to hook up, but could probably pick one up I guess)

 

[cjridert1]

Do most modified dsms hesitate? It 'hesitates' when changing from idle to climbing rpm's. So revving it is odd - the r's drop each time a bit and it thinks about stalling a tad. Do most people have this problem?

 

[cjridert1]

Maybe its timing related? My tim adv goes very high before it gets reduced from knock (tim adv nearly 40 in a pull before knock 'takes care' of it - this is for a 1g). Base timing is 5 btdc.

 

[cjridert1]

For anyone reading/searching this - I took that CAS off - some of the wires' coverings had cracks and wires were exposed. Checked and cleaned all the connectors from o2 sensor harness. Reset timing to 5* and hesitation is gone (this happened before - hesitation was gone for ~a day then came back) its been good for a few days now.