1988 f150 4.9l starts but dies with throttle applied
I've checked the reference line orange/white from tps and get 5v while plugged into tps. Tried a new coil, tried a new icm, and tried to unplug a jumper plug right off the icm connector (said to give the computer control of the spark so says scanner Danner on YouTube) all with same results.
The idle is mostly perfect but occasionally it will dip like 500rpm quick and jump back up. It does this a couple times Till it warms up and then its rock solid. Any throttle applied and it will start to rise and then drop like a rock, if you let off fast enough the truck will catch itself. I have checked the fuel filter and fuel pump and even the return line to make sure fuel is making it all the way through the system and it has full flow. This really seemed like electrical in nature but I thought I'd check the fuel system anyway. Only thing left seems to be the ecm. If that little jumper connector right at the icm connector is infact giving the ecm control over the coil, and the truck does the same exact thing whether that jumper is plugged in or not, am I correct in the logic that the ecm has an internal issue where it cant control the distributor timing advance for higher rpm, and I need a new ecm? |
If you do not verify fuel pressure with a gauge 35-45 psi you are flying blind.
Must verify correct fuel press before moving on to anything else. |
If your fuel side is okay then look at the AIR and unplug your MAF. Check here for more details.
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Originally Posted by hanky
(Post 141563)
If you do not verify fuel pressure with a gauge 35-45 psi you are flying blind.
Must verify correct fuel press before moving on to anything else. |
Originally Posted by heiko
(Post 141565)
If your fuel side is okay then look at the AIR and unplug your MAF. Check here for more details.
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If you have MAP instead, disconnect it and put your airbox and hose back and test drive for 5 minutes or so.
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Originally Posted by heiko
(Post 141569)
If you have MAP instead, disconnect it and put your airbox and hose back and test drive for 5 minutes or so.
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88 F150 4.9L - Fuel pressure specification as follows:
Key On Engine Off: 50-60psi Key On Engine Running: 45-60psi https://cimg8.ibsrv.net/gimg/www.for...31f5d8db2e.jpg https://cimg1.ibsrv.net/gimg/www.for...f45870fef4.jpg |
Originally Posted by heiko
(Post 141575)
88 F150 4.9L - Fuel pressure specification as follows:
Key On Engine Off: 50-60psi Key On Engine Running: 45-60psi https://cimg8.ibsrv.net/gimg/www.for...31f5d8db2e.jpg https://cimg1.ibsrv.net/gimg/www.for...f45870fef4.jpg |
6 Attachment(s)
It will take me quite some time to get you the location diagram. In the meantime I have attached a few pdf for you to work on if needed. The MAP removal is the easiest test I brought up previously you should try first.
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