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Street rod with 91 Ford LTD Crown Vic 5.0L engine which has…

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Street rod with 91...

Street rod with 91 Ford LTD Crown Vic 5.0L engine which has speed density EFI computer. Original problem was engine running rough when driving or dying. Replaced TPS, MAP, coil, new distributor and ICM module. Timed with spout unplugged at 10 BTDC. Runs decent and accelerates good but when spout plugged back in it starts but cuts out badly or dies when you accelerate. Even replaced PCM but same symptoms. What have I missed?

Mechanic's Assistant: Have you metered out the ignition system?

Spark is good and coil and icm both getting 12v. Map and tps are getting 5v from pcm.

Mechanic's Assistant: Are you fixing your LTD yourself? What have you tried so far?

Eng is in 39 streetrod and yes, I built it and wired it. I told you above all the parts that were replaced because of no spark. Found bad connector on ICM and repaired that. Got spark again but now will not run with the spout connected. Timing is correct.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

No I just need to know what can cause this engine to cut out when the spout is connected but not cut out on base timing with all the above parts new.

Submitted: 4 months ago.Category: Classic Car
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Answered in 15 hours by:
12/24/2017
Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 3 months ago
Jaybird61
Jaybird61, ASE Certified Master Technician
Category: Classic Car
Satisfied Customers: 2,311
Experience: Automotive Instructor at Palm Beach State College
Verified

Hi, My name is Jay

Did you replace the ICM before you had connector problem or after you fixed the connector? The ICM uses spout signal from computer to control the ignition timing and is the most common cause of the problem you are having and should be replaced and retested.

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Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 3 months ago

My goal is to give you the best experience possible! I hope I have earned a 5 star rating! Please remember to rate my service by selecting the 5 stars at the top of the screen before you leave today. If you need more assistance, please use the reply box and let me know.

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Customer reply replied 3 months ago
Problem started with a rough engine on acceleration and became a "no spark" at all. That's when I replaced the distributor with new ICM as well as the coil and noticed the 6 pin connector was loosing connection when that did not work. Replaced 6 pin connector on ICM which was part of a brand new Ron Francis wiring harness. Now, it starts and runs good setting timing at 10 to 12 degrees btdc but will not run correctly when the spout is replaced and the computer takes over command of the timing. Checked timing with light and it does advance the timing when the spout is connected and it is holding steady at idle at about 20-22 degrees btdc which I think is what it is supposed to do. Has new PCM installed. Seems like some sensor is telling the PCM the wrong value when throttle is pushed. TPS is also new so I haven't checked voltage out there. I don't think that the signal out from it or the MAP sensor were bad but changed them anyway. I'm stumped. This 5.0L engine has speed density controlled PCM and installed with new Ron Francis EFI wiring harness. New startup but has been started before and ran decent but not road tested until lately. Went from running rough and dying driving slowly around the area to a no spark issue with the connector and now that is fixed but won't run correctly with spout connected (computer in control of ignition). Tell me what is going to fix it. Thanks, Lanny
Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 3 months ago

I am not sure what can cause this on this vehicle and will opt out for another expert that may have infor for you. Please do not rate or respond until another expert contacts you first.

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Classic Car Mechanic: Matt, Engineer replied 3 months ago
Matt
Matt, Engineer
Category: Classic Car
Satisfied Customers: 22,908
Experience: BEng Hons mechanical engineering 20 years repairing my own cars and others, 8 yrs in formula 1 engin
Verified

Hello Lanny

another expert here I'd say that this could be a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent a vacuum from being created as the fuel leaves the tank to the engine
If this helps then replace the cap with a new item

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Customer reply replied 3 months ago
Not a fuel issue. New fuel pump and filter with measured constant 41 psi fuel pressure. Filler cap is vented and working fine. As stated above, this truck runs fine without the spout wire connected. Electrical or sensor related problem. Has to be something that effects how the computer sees the throttle or fuel needed when the timing is controlled by PCM. Did you read my original post of what is happening?
Classic Car Mechanic: Matt, Engineer replied 3 months ago

Hello

OK if it runs OK with the MAP sensor disconnected but falls over when its connected ( I'm assuming thats what you mean when you say 'spout') then have you checked the vacuum tube between the MAP and inlet for leaks or blockages?

also checking the inlet manifold for cracks and vacuum leaks would also be wise

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propaneor brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion will make a leak worse) so leaks can be better or worse as the engine heats up.
1 vacuum leak path that you won't find with the above test is if the brake servo is leaking

so try clamping off servo hose to see if this has any effect

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Customer reply replied 3 months ago
A mechanic should be familiar with the term "spout connection", it is common term for spark out from the ICM (ignition control module). It has nothing to do with the MAP sensor and has no vacuum line to it. These conversations are going no where and everything that has been mentioned are all over the ford forums for free. I'm sorry but I'm not satisfied with playing text tag with you guys and explaining to you things that I have already told you were checked out. I'm going to request a refund. Thanks for you efforts to this point. I will not leave a bad rating, I'm just not getting any answers , just more conversation.
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Matt, Engineer
Category: Classic Car
Satisfied Customers: 22,908
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Experience: BEng Hons mechanical engineering 20 years repairing my own cars and others, 8 yrs in formula 1 engin

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