1994 4.9L engine will not start, what can it be?

10

Asked by Dec 09, 2014 at 12:14 PM about the 1994 Ford F-150 XLT LB

Question type: Maintenance & Repair

I've tried everything. Had others try what they can think of. Nothing works. Can't start so
can't get a code. Replaced the injectors, have 50+ pounds of fuel pressure. The
injectors fire. Replaced pick up in distributor, coil, plugs, wires, even tried another EEC
module and still nothing. Will crank and will some times start with starting spray but will
not start other wise. Some one said they thought maybe something in the wire
harness? But I checked and have continuity where I should, power where that should
be...HELP!

13 Answers

102,005

If everything is as you say then it has to be an engine problem ie no or low compression, cam timing wrong, major vacuum leaks etc. You still should be able to do the key on engine off EEC test even though you can't start it. Are you sure your EEC system is getting proper voltage and grounds, I've seen a lot of Fords have grounding problems. Also make sure your injectors are getting battery voltage and a good trigger signal from the ECM.

1 of 1 people found this helpful.
10

We checked the compression and it seems pretty good. The EEC test engine on, not running gives me an air circuit error (I don't think that really has much to do when not running) No other relevant codes. The grounding issue has been suggested, and I ran some continuity checks and everything related to the EEC seems good. I used one of those injector node kits (the blinking light testers) and we even took the injector rail out and I held it while my partner cranked the engine and we have injectors firing. My suggestion was to pull the timing cover off and look at the cam gear, but my partner said he had it running with starting spray, but I've never heard it run with or with out spray....so I can't confirm.

102,005

If that engine has a mass air flow in the intake tube then yes it can cause a no start, unplug the sensor and see if it will start, if it does it might not run very good but you have verified your problem.

1 of 1 people found this helpful.
10

If you are referring to the large air flow control near the air filter on the fender, then, no this one doesn't have one....My 1994 5.oL has one but the 4.9L does not....There is the idle air valve on the throttle body, but not the air intake before that.

102,005

OK good, Try this: disconnect the O2 sensor first, then try to start it, if still no start, then disconnect the ECT sensor, try to start, if still no start disconnect the ACT sensor, try to start, hopefully it will start then, if it does then reconnect the O2 and start, if it starts, good, if it don't, replace O2 sensor, reconnect the ECTsensor, if it starts good, if not replace the ECT sensor, reconnect the ACT sensor, if it starts, good, if not replace the ACT sensor. If this makes it start then disconnect the battery negative cable, turn on the headlight switch for at least 30 seconds, this will discharge the capacitors, turn off the headlight switch, reconnect the cable, start engine, let idle stabilize, then drive as you normally would. Hope this works.

1 of 1 people found this helpful.
10

I know where the HO2, and the ECT sensors are located, but not sure where the ACT is. Is that near the front of the engine before #1 injector on the intake??

1 of 1 people found this helpful.
10

I found the ACT sensor...I'm going to go give it a try in a little bit, and will let you know how it went. Thanks.

10

I tried doing what you suggested and still nothing. I'm still leaning towards the cam gear lost a tooth..... The owner said it began running bad and steadily got worse until it just quit one day. He took it in and who ever that was said his timing (distributor) was out of whack. They reset it and it ran again (but not real great) and then it just quit again and that was the last time it's run. I think the can gear has lost a tooth and jumping one tooth every now and then.......Now it is too far out to run....what do you think?

102,005

Now I get the picture, check the pin on the distributor gear, it may look good but it could be sheard off internally, while the distributor is out look at the cam drive gear and hopefully it looks good. That maybe your problem.

1 of 1 people found this helpful.
10

We already replaced the drive gear on the distributor while we had it apart changing the pick up in the distributor. The cam gear looks good also...... Do you know of an easier way to check cam to crank gears short of pulling the cover off?

102,005

Put engine on TDC, watch the distributor rotor as you slowly turn the engine backwards, when the rotor just starts to move stop and see how many degrees it is showing, that will measure the slop in the chain but the only true way to do it is to pull off the cover.

1 of 1 people found this helpful.
10

The 4.9L doesn't have a chain...it's gear to gear...... Slop will not be apparent.....If anything there would be a tooth broken letting the gear jump time..... I guess we're looking at pulling the cover off then...It was suggested I go to TDC on #1 then back up crank 108 degrees and see when the intake valve begins to open.... should open right close (a few degrees off BDC) turning backwards...... Does that sound right to you? Then the next step might be to pull cover....

10

Sorry...that should have been 180 degrees not 108....my bad

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