I have a 91 F250 with shorty headers and a small cran cam designed for computor controled trucks. I have good idle and the truck drives well until you get it loaded down with a trailer. Then it acts like it is running lean, under part throttle cruse when you go up a slight hill fully loaded you get a little surging and some slight spark knock at times even with 92 octane. I have cecked the pulgs and they do look a little on the lean side, very white insilator. I am only getting 40 psi fuel pressure key on engine off and about 34 with the engine running at idle. If I increase rpm I can actualy get it to go as low as 32. Seems to go up ok at WOT but 32 just seems to low for an off idle reading. Manual says 30-45 but doesent specify how they get those numbers. I am thinking perhaps a new regulator might help this out. If I pinch the return line I can get 60 PSI . Has anybody here tried an adjustable regulator to increase fuel delevery on a mildy modified 351 like mine.

 

I wonder if you might need bigger injectors? Youre possibly flowing a little bit more air(Dues to cam and headers) and even though the computer is telling the injectors to pulse properly, they just dont quite deliver as much fuel as they need to(Due to the higher air flow). Just a thought. Also, swapping out a regulator isnt a big job.

 

Your FPR is probably fine. If it goes above 45 PSI and you have fuel in the vaccuum line leading to it, then thats when you know its bad. I dont recall a bad FPR causing low fuel pressure. I could be wrong though.

 

How are you getting this, are you grounding pin #6 of the DLC (Test Connector)?
IF not the 40 does not mean anything, if you are then I would replace the FPR. That is a good reading. You need to check with a vacuum gauge here to see if the vacuum changed. You can also pull off the vacuum hose from the FPR and see if it goes to 45 psi. Hold your finger over the end of the hose while it is off.You need to check with a vacuum gauge here to see if the vacuum changed. 30 is with max vacuum and 45 is with no vacuum (WOT).Sounds like the pumps are OK but you might want to check the filters. Your flow rate may be down and if you checked the fuel pressure under load if may go way down.

 

Is this a SD motor or do you have the Mass Air conversion kit on it?
Is your air pump still in place, plumbed correctly and working? The steel air injection pipe on the back of the motor between the heads is known to rust out, and can cause the symptoms you describe when this happens.

Increasing fuel pressure won't help because the computer will just trim the injectors to lean it out again. The stock 19lb injectors are good for 275hp peak at 100% duty cycle, but you're nowhere near this at cruising speeds.

 

i would pull codes . www.fordfuelinjection.com will show you how

 

Thanks for the info guys. I will check my pressure again with the regulator vacume line disconnected and see if it will go to 45 PSI. the motor is a SD set up. I will pull the codes and see if it is telling me anything, but I know it's lean by looking at the plugs. Not sure the computor would know if I upped the fuel pressue either unless I went too high and had it running rich then the O2 sensor might try to correct it but I think the range it can adjust to is pretty limited. I will do some more testing tomite to try to rule out the regulator. Ho often do MAP sensors fail. I also wondered if it might be worth checking the TPS. It is a 15 tyear old truck and I have changed none of the sensors.

 

if any of those sensors are acting up the computer will tell ya

 

Am working on getting codes by using check engine light. OBD1 is all two digit codes correct?

 

Not necessarily. My 95 F-150 had 3 digit codes. My 91 Ranger had 2 digit codes.

 

I think it depends on if you have an EEC (Electronic Engine Control) computer or a PCM (Powertrain Control Module).
The EEC is two digit codes and the PCM is three digits and I think they overlapped a few years.
They had to go to three digits on the PCM to list all of the Transmission codes and the EEC did not control the Transmission.
Of course the old ECM (Electronic Control Module) computer was two digits but it did not control the engine, just the Emissions.

 

It looks like it has three digit codes, tried to get them all by writing down the number of flashes, has alot of codes stored for sure. I think I will just spend the $30 and go get a code reader. The truck does have the E40D with electronics so am pretty sure I was getting three digit codes. Hopefully they will point me in the direction I need to go. Am kind of surprised with that many codes I don't have light on all the time.

 

Makes sense now! My ranger is a manual, and my 95 is an automatic. Thanks for clearing that up!

 

I have the results of the testing so far and I think I have found a possible answer. I forgot to mention that the EGR is disabled as the lightning headers have no provision for EGR hook up. Upon reading all the information on Ford fuel injection.com and reasearching on this site it sure seemed like no EGR could cause lean out and knocking due to exsessive spark advance. I installed an EGR eliminator and I don't seem to throw any more codes except the one for EGR not opening. Before I was geting 171,172, and 181. Looks like I was at limit of O2 sensor adjustment and still lean. I will drive the truck to work for a few days and see if any more codes come back. It still seems like it has a little hessitation when in overdrive under light part throtle, very similar to surging you get when a car is a little lean. So I am wondering if a slight bump in fuel pressure might help. It looks like my fuel pressure is good as I get 34-36 at idle and 45 with vacume hose removed from regulator. I am going to go ahead and change the fuel filter since I have one already. But I am now wondering if it might be possible to do a little more tuning with an adjustable regulator and optomize this set up for the cam and headers. I know a custom chip would probibly not be a bad idea also.

 

I think you have that backwards, if you block off the EGR it will run richer not leaner and this will cause a shorter engine life (fuel washing the oil from the cylinders) and fewer MPG.
If you installed an EGR eliminator and you are getting EGR codes your eliminator is not doing its job. That is what it is there for.
Are you running your timing at stock (10* BTDC)?
If not that could cause the pinging.
As I think was stated above or in another Thread, upping the fuel pressure will cause a richer mixture, to get that you have to do some EEC tuning.

Someone a while back was saying that you could get more power out of the truck by changing the EEC out with one from a Van. I do not know if they dump more fuel or the timing is different.