7.4L TBI fuel pressure problems

[Bentone23]

I am experiencing 14 psi fuel pressure and engine hesitates under load and will not rev past 3100 rpm. I replaced 2 fuel filters and Oberg was clean as a whistle. I replaced the fuel regulator in the TBI. But suspect it is still bad. I squoze the return line with pliers for an instant while the engine was running and fuel pressure instantly shot to max on the dial. I am certain the fuel pump is good now.

My question, is there different fuel pressures that Crusader or Chevy used on different models?

Any more ideas?

I already pulled the fuel draw tube from the tank, and the tube was clean, the anti siphon valve was moving freely and had a little of what appeared to be pipe dope on it. It was not clogged in any way.

The starboard engine runs up to 4000rpm and has had no issues. It has 20 psi.

Any ideas? Am I barking up the right tree?

[bud37]

Yes there are different pressures....did you replace the regulator with exactly the same part as the good engine ??
Wouldn't be the first bad part from the box.
Is the voltage at the pump ok and stable ?
You appear to have checked off the fuel line/ filter stuff....

[Cooler]

Bruce - do you hear any popping sounds when you get to 3100, or is your tach jumping around?

[cpoint]

I had lots of problems as can be seen on all my posts in the past, finally found out it was the injectors causing the problem. Which were fouled up by bad fuel. After 2 years of tach jumping like crazy, getting nowhere past 2500 RPM, last year thanks to my new mechanic, was resolved. I am not a technical guy on engines, and I may be way off on your issue, but sounds like the problem I had for little over 2 years.

[Cooler]

Yup, that is exactly what I was getting at. Tach jumping and popping sounds are caused by plugged injectors. They get a varnish like layer inside the injector, which reduces the fuel flow and can cause pre-ignition and/or detonation. This is created by bad gas ( low octane ), especially ethanol treated gas. Ethanol breaks down pretty quick and drops octane while sitting for a while in the tank. A good mechanic can test injector flow. The injectors can be cleaned, or rebuilt, or replaced, depending on severity. Crusader usually shows an example of detonation in the fuel requirements section of their operation guide. How this relates to PSI, I don't know. Hope this helps. Side note: there are a lot of marinas changing over to ethanol gas, due to demands by the charter industry. Those charters burn through gas real quick, so the marinas have to comply with making cheaper gas available. When you fill up, always check to make sure you are getting non-ethanol if that gas is going to sit in the tank for a length of time. We had 3 marinas flip last season, but they didn't make that change known. Can't blame them, they need sales, but I want pure gas in my tanks. Sometimes it sits for several weeks. My mechanic showed gasoline phase separation in a jar of 10% ethanol gas after a relatively short time. Sorry, went on a little rant there. er

[km1125]

Is your pressure regulator referenced to manifold vacuum? I don't know on the throttle bodies if that's required or not, but it is definitely required in the MPI.

[bud37]

If this is like the auto TBI, I think it is a bypass type reg with an internal spring....much like an oil pump......you can change spring colors or shim to fool with pressures if the injector size is altered. If the pump is bad then that reg could close up and keep the engine working just fine until there is a need for more fuel volume, then ya got a problem......not sayin this is what is up here, just my take on how this system works when all its parts are right.....

[mjk1040]

Guess we all should be looking for a real good additive to put in our tanks as a precaution if the marinas are going to play this ethanol game on us! On another note, if you think your marina is slipping you low octane gas for higher assumed octane gas by the pump label, call the local weights and measures people that sealed the pump and demand a EPA sample be taken. The number should be on the seal on the pump. I don't know if this would apply to our northern boating buddies in Canada!

[tomschauer]

It sounds like many of you still have access to non ethanol fuel. In my area, it has been gone for many years. There are still a few gas stations, and they are very few and far between, where you can get ethanol free regular 86-87 octane fuel for about a 20 cent premium over premium 91-93 octane 10% ethanol fuel. I haven't seen ethanol free fuel at a marina in our area for at least five years. Many local marinas just have 89 octane 10% ethanol as your only choice.

[tomschauer]

Mike, something I will have to look for in our area, I don't think the marinas in my area are subject to the bureau of weights and measures as marine fuel is not subject to road tax, even though they charge more for it than the taxed fuel. I will look for the seals next time I am at the marina., but I am pretty sure they aren't there.