Hello Ya'll, I was driving my 88 f350 today, 7.3 5spd and I noticed it won't rev over 2700 rpm. Runs great till that point then falls flat on it's face. No abnormal smoke or noises.. Any Ideas? Thanks

 

well personnaly i thought the redline was 3200rpm or somethihng really clsoe to that but no 2700rpm doesnt sound right as max out. although iv only done that to my truck 1 or 2 times

 

how many miles?? it sounds like your injector pump is failing.

 

Mine did same and after installing new mechanical fuel pump, plus a electric fuel pump booster, problem went away and engine will spin to 3600, do not recommend this maximum rev limit but it does show if the engine has good fuel supply and good air flow it will rev out well, and there was a marginal power increase with these 2 pumps installed in series. I suspected fuel starvation was the problem as engine accelerated well until it hit about 2800 rpm range.

 

A side note for netmaker:
The general consensus I've seen with regard to electric pumps is that you should not feed the mechanical lift pump with electric. Pull it out of the loop and block off the plate with a big block chevy fuel pump cover. Too much input pressure to the mechanical pump can cause the diaphragm to rupture filling your crankcase with diesel.

FWIW,
Mike

 

understand the problem so that is why I fitted new pumps and the electric is a 4 to 6 lbs rated unit. Tried just electric but still had starvation issues so added new mechanical and what a difference with 2. Instant starts at all times as electric pressurizes fuel lines immediatly key is turned and fitted fuel pressure gauge at outlet of final filter to injector pump to monitor output.
Originally read a post on the 6.2 Chevy diesel site about a similiar modification and the success of that 2 pumps in series.

 

Run two electric pumps then.
A ruptured diaphram in the mechanical pump will cost about 7,000 dollars to fix.

If you fill the crankcase with diesel, by the time you notice something wrong the engine will probably be junk.
Diesel is not a very good lubricant.

Remember the stock lift pump was not designed to have pressure to the inlet.
Pressure in means more pressure out.
More pressure means ruptured diaphram sooner than later.

 

If you really want to keep both of them in series, reverse them so that the mechanical feeds the electric. That way if you have a ruptured diaphragm in the mechanical the electric will suck air instead of pumping your crankcase full of diesel....

 

Have considered the 2 electric pump option and may yet do that. The reason for the electric before the mechanical is that the electric specs list a higher suction capacity than the standard mechanical and we found the electric really primes the fuel very quickly and that well known benefit of no need to turn engine over. I originally had a 7 to 9 psi electric by itself but when the starvation issue arose I decided to reinstall the mechanical and replaced the electric with a lower output electric, 4 to 6 lbs, to keep pressures low at mechanical and at outlet of final filter to injector.
One reason for keeping a mechanical in the system is that my research kept coming up with the best pumping solution was to run an electric for good starting because of immediate priming of fuel line, immedaite pressure to the injector pump and then the need for a mechanical that responded with high fuel volume as the revs went into the higher rpm range. This was where the electric pump appeared to fail unless it had a capacity of about 50 gals per minute. There is an article on the dieselmanns site that explains the problem with electric pumps maintaining sufficient fuel volume at high revolution demand times.
The monitoring pressure gauge is fitted to the final filter outlet and is adjustable and I originally found that I was pumping 9 psi to the injector pump, with both pumps working. I have now reduced it back down to the specs of 2 psi with a high volume of fuel delivered. I can run excess fuel / pressure at the gauge back into tank return line. I was working on the premise that the injector pump delivery pressure must never exceed about 15 psi or damage could take place to the seals.