454 XL TBI rpm issue

[390Express]

Source of the post

Source of the post From what I can tell from digging into the MEFI 1-2 diagnostic manual, there's nothing in the ECU that provides a higher idle, that would otherwise make it stall later.

It's not really the higher idle, but all engines have to run a bit richer when starting from a cold start. Fuel injected engines run rich for a period of time, which can be a timer or by measuring coolant temperature.

The ignition observations are interested. Seems like you need to understand what's going on there. Can you put the old dist in there for testing?

Real time data stream on the scanner is fine. Everything looks normal, until it stalls. The issue presents as more of a fuel delivery issue, despite all evidence to the contrary (fuel pressure is good, fuel pump continues to run while stalling, injectors continue to fire as its stalling), so I'm going to try swapping out TBI uppers prior to swapping the distributor. I suppose it's possible for the regulator to allow proper bleed-off pressure (which is what's measured in the line), and not allocate proper injector pressure. It's about a 30-40min. swap to do both TBIs. This will eliminate the fuel pressure regulator and the injectors as potential problems.

If that doesn't fix it, I'm going to swap distributors rather than put the old one back in (another 30-40 min. swap). That's really all there is left, besides the wiring harness.

After those two potential problems sources are ruled out, I will have literally done every other damn thing I could do, other than internal engine components, and tracing issues at the harness. (recently pulled the 9 pin, and added Nygel... only other electrical component(s) that I could possibly swap are the breakers, but voltage checked out fine from one side of the breaker to the other while it was stalling)

[390Express]

Pretty sure I fixed the damn issue. I think the culprit was 3-4 little dots of rust in the injector cavity (but I don't see how it would effect anything... the screens over the injector pickup looked fine, and the regulator looked fine; untorn and the spring looked brand new)

Swapped upper TBI units and it fired right up, and kept running. Not sure if the injectors are bad, but everything else inside looked good, other than the couple dots of rust. Injectors on that motor are brand new, and had a nice spray patter... I'm going to have to investigate further as to the actual cause, but at least I seem to have found the solution.

In any event, hopefully splashing tomorrow. Thanks for all of the direction and advice!

[Bentone23]

It turned out to be the fuel regulators. The original Crusader regulators for the 7.4 TBI fuel injected engines are 30 psi. Some previous owner or mechanic went to an auto parts house and put 10 psi regulators from a light duty pu motor. I found a guy in Washington State who knew about this and sold me the correct ones for $38. No more stalling, misfire, or check engine lights. And that was 3 years ago.

[g36]

Bentone23 thanks for posting the info on the fuel regulators could you also post the correct part numbers for these?

[km1125]

Thanks for posting the update, but I'm a little confused. You only had this issue on the STBD motor, right? Was the fuel pressure on that motor always lower than the port motor? Didn't you (at one point) swap the throttle bodies? Did you change both pressure regulators or just the STBD one?

Earlier in the thread, you posted "the earlier models will have 10-12 PSI (1995/1996), the later models will be higher (I believe there are two versions, 22psi for TBI and around 43 psi for the MPI style)." Where did that data come from? It sounds like you got different specs from the guy in Wash St.