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Discussion Starter #1
Hey guys.

I searched the forums, but didn't see something specifically like this. I have not run codes because my suspicion is the in-tank fuel pump, but I'm hoping it's something more like the in-rail pump, or simply a filter, or something else easy to get to/cheaper.

What goes on is during a cold start. Key on/engine off: I hear all the normal things turning on. Once I turn the engine on to start, it takes a few seconds before the gas hits the engine and it stumbles and putters into starting. It totally sounds like an old prop-engine airplane starting up. The puttering doesn't happen later in the day, just at the first start of the day. Sometimes, it takes two cranks of the key to get er goin.

The RPM's climb during the "warm up" or whatever goes on during the first bit of the engine being on, and then the RPM's dip for a brief second to almost 1k, then it jumps back to the high RPM range it was during the last 20 seconds. During this time, the engine is running smoothly and solidly. As soon as the engine is content at waking up, the fuel pressure drops so low that the engine almost stalls. Once in blue moon it actually does die. (If it does stall, turning over isn't an issue at all.) Then over the next 10 seconds, there is a rhythmic roller-coaster of RPM's climbing and falling, as it seems the engine gets a spurt of gas, the RPM's fall, then it gets another spurt of gas.

Sounds like the fuel pump going out, right?

Here's where it gets confusing (to me, anyway), and makes me not think it's simply fuel pressure: Once I put it in Drive (even if I do it in the middle of it's little high RPM warm up), the engine runs great. There is no stalling, it climbs hills fine, it accelerates fine, there is no hesitation when hitting the gas, it idles steadily when at stop lights, it doesn't stumble when taking my foot off the gas - after it's little start up dance, she runs great. In other words, gas pressure seems fine after the engine gets into Drive.

(I've also tried the bit of not hesitating once I turn the key On and went immediately to cranking to see if the initial spurt of fuel pressure to the engine makes a difference, but it takes the same amount of time cranking.)

Previous to this (it's been a slowly growing issue over the past year of me owning the truck), I've replaced the fuel pressure regulator and the throttle positioning sensor (and cleaned the throttle body when replacing the TPS) when these symptoms started up, roughly 8 months ago (it's not my main commuter). I've got a fuel filter on order with a code reader.

I have picked up that the rail fuel pump dishes out most of the pressure, but I don't want to be replacing the wrong pump. I don't know when the last fuel filter was installed by the prev owner. Ideas?
 

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Premium Member
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23,549 Posts
novel idea here. Why not put a pressure gauge on the fuel rail and see what the pressures actually are before throwing parts at it.

also your year may or may not have 2 fuel filters.
 

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Roller rockers are gay
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19,191 Posts
i agree with jopes, putting a gauge on it to actually SEE the pressure readings instead of imagining it would be a great idea.
 

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Super Moderator
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26,956 Posts
yo,

'88 Single-Function Reservoir

Used on '88-89 Broncos & F-series/E-series/Rangers/others with single tank dual-pump EFI. In this version, the only moving part is the tank-side inlet check valve. The return ports flow freely and are NOT connected to the reservoir. The engine-side supply port is open to the reservoir.

To test it, unplug the frame fuel pump, disconnect the engine-side supply (large) line, and cycle the key. If fuel flows out of the reservoir nipple, the reservoir is working normally. If not, disconnect the tank-side supply (large) line, and cycle the key. If fuel flows out of the line, the reservoir check valve is probably stuck, or its internal filter is clogged.

A reservoir marked "DO NOT REMOVE CUP" does not contain a filter. For a replacement O-ring for the cup, buy a NAPA 3268, Fram CG3862, or equivalent filter.



See this:
http://www.supermotors.net/registry/media/477914_1
 

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34 Posts
Discussion Starter #5
thanks to you three for the fast response and smacking a little sense into my head on this fine morning, and for the info links :doh0715:

this is why i come to this site. y'all kick ass.

i'll return with findings.
 
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