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1998 7.4L Crusaders (MEFI 2) rpm surging

pgavazzi

pgavazzi

New member
Sorry for the long post…

One engine (starboard) runs perfectly… at idle and higher rpm
The other is experience rpm surging (idle and running ~ 120 rpm variance) and top end (>3200 rpm) limited performance.
1200 hours now, Heads and Manifold replaced at 1100 hours; Not burning oil (lower end looks good… minimal wear ridge)

Both engines ran well (idle solid @ 650 rpm, WOT @ 4400 rpm) for about 100 hours.
Port engine developed miss… Distributor cap and rotor where damaged (looked like a condensation problem)

Changes: (New) Injectors, coil, ignition module, Map sensor, TPS, IAC, swapped Distributor, Timing is dead on at 10 degrees.
Replaced Fuel pressure sensor; think I might have the wrong one (pressure @50 psi, Starboard @38) going to swap it back to the original next)

Biggest difference in the Rinda data is injector pulse width, map sensor voltage, Fuel flow rate.
So, could be vacuum loss somewhere, throttle body issues, etc.

My next steps are:
  1. New plugs and wires
  2. Compression test
  3. Swap starboard and port plenum’s on up… (see if the problem moves)
I am almost at my wit’s end here. Any suggestions?
 

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Ignore the post. #4 cylinder has very low compression, not even registering on the gauge. All the others are in spec. (140-160)

Off with its head eh!... thanks for interest
 
Not knowledgeable on Crusader but MEFI 2 fuel pressure is normally in the 40 psi range and not 50. This is just a guess because I would need to research more to find out.

Best not to throw parts at a problem because those parts can also induce more issues
 
Rather mute at this point but I wouldn't ignore the delta in the "battery voltage" parameter...It may still be a contributor once the dead cylinder issue is resolved...
 
Guilty! I did throw some parts at this problem… Don’t regret the injectors (26 years old); it was time. The others did not amount to much expense or time and what the hell… Da Nile is not just a river in Egypt. I was doing everything to avoid the head removal and possible lower end catastrophe. Just back from dropping the head at the machine shop… it’s the valves and springs.

It all started with a low RPM velvet drive clunking (gear lash)… Understood to be some kind of engine miss generally. Learned a lot about MEFI and MPI and now have the root cause.

Thanks for the feedback.
 
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