Hello,

I'm stuck. Truck will not start. I have a 1987 f150 4.9l. I have replaced plenty over the last 6 months. In the last month after driving a few miles it stalls at red lights. When i step on the gas its almost like its not getting any or flooding. I'll coast into a parking lot and let it sit for 15 or so min. and it will start up again. Only for it to do it again. It will back fire also. On cool days this doesn't happen. It was idling at about 1100 rpms. Fuel is rich. RPMs Surges at when starting the levels out. But this weekend it now will not start at all. Ok so things to rule out. I have replaced. Plugs, wires, distributor, coil, starter, started solenoid, battery, battery cables, bypassed the inertia switch, fuel pumps, fuel filter, all six fuel injectors, fuel pressure regulator, pcv valve, water pump. fuel Pumps have pressure. I'm thinking MAP sensor but wasn't' sure if that could cause a no start. No vacuum leaks. Help!

 

Yes, a faulty MAP sensor can cause a no-start condition. Before spending anymore $$ check for codes by running the Key On Engine Off (KOEO) tests and Continuous Memory (CM) display. List any codes you receive by number (two digit) and when they were displayed.

I do not see where you actually tested the fuel pressure and checked for spark?

 

Ive never tested for codes how do I go about doing that? I checked the fuel pump for pressure and it just about blew the fuel filter off. Spark plugs are about two weeks old.

 

You'll need to follow the instructions here: EEC IV Self Test hookup . Be aware that most '87 trucks I've come across do not have the yellow check engine light wired to anything, so you will need the test light or volt meter to count the blinks.

 

I did not ask about the spark plugs, I asked if you have spark, i.e. is there spark at the plugs?

You need to rent/borrow/buy a fuel pressure gauge to test the fuel pressure at the test port on the fuel injector rail.

 

That makes sense about the check engine light. I did a quick youtube search after rreading your post and nothing blinked. Yes I have spark. I put in a new map sensor anyway it was only $40. But that didnt work. It was worth the shot. The test port on the fuel rail. Is that the **** I saw in the back of the rail where the fuel lines connect to the rail? I may have to take the manifold off to get to it. Thanks for you help and direction I felt like I hit a wall and im the kind of guy that never ask for help.

 

I tried to get the code. I tried both jumping it and the test light and only got a continuous light no blinks.

QUOTE=rla2005;13364140]I did not ask about the spark plugs, I asked if you have spark, i.e. is there spark at the plugs?

You need to rent/borrow/buy a fuel pressure gauge to test the fuel pressure at the test port on the fuel injector rail.[/QUOTE]

 

I had similar issues with my '92 F250. My issue ended up being the Throttle Position Sensor. I put a new one in and all is well now. If it is not starting it may be possible that your MLPS is not working properly. I believe a bad MLPS will cause a no start.

 

yeah i know i look up symptoms and it seams as though the symptoms are similar to many things. like the map sensor. I'm doing a compression test tonight and hoping its nothing to crazy.

 

There is usually a black cap covering the test port. I have never owned or worked on a 4.9L engine therefore I cannot tell you exactly where it is located. You should not have to remove the intake to check the fuel pressure.

 

That is a bad sign. Use some contact cleaner on the data link pins or use a small screwdriver/nail file to remove corrosion. If that does not get the PCM into test mode perhaps it is bad.

Remove the PCM, open the case then inspect for signs of moisture, burning and/or leaking capacitors. This is becoming a very common occurrence.

 

Ok yes i have seen the black cap port when i was changing the fuel injectors. I didn't get do anything i wanted last night. Its been raining almost every day here in south Florida. Never mind the mosquitoes and humidity. I'll check tonight. My manuel does not show very well where the pcm is located. Says its behind the kick panel and the picture has an arrow pointing to the clutch pedal. When i bypassed the inertia switch it did have burning on the connector there. I'm wondering now could the two be linked with burning. I'm also going to do a compression test. Would low compression in a cylinder change in cold or warmer weather?

 

PCM location:

courtesy of subford

On your model year truck it comes out from inside the cab.

Temperature will affect compression readings. It is suggested to warm up the engine before checking it.

 

Ok I located the pcm your pic was way better. I didn't pull it out yet but I did get to the compression test.

Compression test results.
1. 140
2. 130
3. 70
4.150
5.140
6. 120

Wet. Same except 3. Jumped up to 90.
Does this mean I need a valve job? If so do you have any idea what an average cost for a machine shop to service?
Also this morning I decided to spry starter fluid and finally it started. I let it idle for 10 min then when i hit the gas it would hiccup. If i slowly pressed on the gas it was fine. Took it for a drive. I stopped to get gas. It started just fine when i was leaving got to the first light. Idled rough then when it was green i slowly pressed on the gas and bam stalled. After a hard start i reved it up and took off and was fine till i got it back home. Any thoughts?

 

I have a 91 4.9, did the same thing and it was the MAP sensor..located under hood,, back firewall..left side.. I know you will get aa lot of more educated answers but from experience and your description, 100% the map sensor..