My friend has a 98 24v and the stock LP took a dump so he put a 100gph carter on it and took the fuel line strait from the carter to the fuel filter housing and bypassed the stock LP and now it starts hard, Any Ideas??? we checked for any possible air leaks and we cant find anything that would be causing this

 

how does he have it wired in?

 

X2 if he doesn't have it wired in to be controlled by the ECM he could be over pressurizing the VP which will make for hard starts.

 

He wired it in using the stock LP power source

 

just for grins try a different lift pump like a stock carter....we have seen more then a few cases with the airtex replacement pumps cause a hard start, after talking with bosch about the problem it seems that the ecm calulates the pressure by reading the amp draw on the lp circuit and the pumps are not drawing the same current and it sends a false signal to the ecm and causes a hard start, i've even heard of this problem with the fass direct replacement pumps but i think they have since fixed theirs

 

Ok wil try that, Thanks for all the help man! I greatly appreciate it!

 

no problem, let me know if that changes anything

 

A hobbs oil pressure switch will bypass the ecm. That's the first time I've ever heard the ecm makes pressure calculations according to amperage draw speculation.im going to do some research on that subject. Considering the variables it would be difficult at best but in the same respect I rarely use factory fuel systems or ecm/pcm wiring.

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i didnt get to talk to bosch myself but the injection pump shop that i get my vp44s from did talk to them directly for me while we were trying to figure out a hard start condition on a truck which we had just replaced the injection pump on and that was the answer that we got from them, since finding this out we have fixed half a dozen other trucks that were having similar problems and all of the trucks had the airtex pumps on them and the only thing we done was swapped them back to the OE carter pumps and their problems went away. it was the first time i had heard about this amp reading to pressure also but after hearing that and thinking about it then it did make some sense to me since there is no fuel pressure sensor anywhere yet you read on the forums all the time that high pressure will cause a hard start. i do know of one truck that is running a mechanical lift pump at 35psi yet he dosnt have a hard start so if the ecm was reading the actual pressure somehow then that truck should have a hard start and it dosnt, and yes i know that much pressure can crack the diaphram in the pump and i did advise him to regulate the pressure down below 20psi

mystery maybe you can shed some more light onto this subject it would be some good information for everyone, i wish i knew more about it but that is the extent of my knowlege on the subject since i didnt get to talk to them myself