OK guys I have a problem.

My truck is an 89 f-150 with a straight six. It has some problems starting, it doesn't always start right up like it used to. This problem seems to be worse in the warm weather. The motor has to crank over many times before it starts. When it does start it fires on maybe 4 cylinders for a few seconds before going up to 1500 RPMs to warm up. It idles just fine and runs good when it starts. I can hear the fuel pump switch on and I think the motor would cut out under a load if the pump was bad. I replaced the spark plugs (which were shot) and that seemed to help some.

Any help would be very much appreciated, I was thinking it might be the O2 sensor??

PS the "check engine" light will sometimes blink on when I accelerate, but it never stays on and it only happen certain times.

Thanks again

 

I'd look in other areas, other than the O2 sensor. I'd start with ensuring a good strong spark (pull a plug, ground it to the block and turn it over) and that fuel is getting to the cylinders. Crank it like normal, but after 3-4 seconds, pull a plug, smell for gas.

I'd be looking at coil, distributor cap/rotor, engine control module, and then fuel line pressure leak or weak high pressure fuel pump. To check for fuel pressure leak, turn key on and off 5-6x leaving it on 3 sec each time, then smell for gas. Do it again, this time see if it cranks quickly. Turning key on and off helps it build pressure and gets the gas right to the injectors before it leaks down.
That's where I would start looking. This site is full of master mechanics and they can probably give you some better ideas.

 

i have to agree with Stephens here. maybe also try replacing your coil too

 

Thanks. You can check your coil just by pulling the wire cap off of it. Crank the motor, if its a good coil, the spark will jump to the block (3" or more).

 

My 300 always jumps up to 1500 rpm when I first turn it on and then it goes away. I know a couple other people on this forum who it happens to also.

 

Sound advice so far. Even so, DO NOT THROW MONEY at the problem until you are sure of the problem. Go to this site and learn how to read your truck's computer for error codes and then go from there. All it costs is some time and a scrap of wire.

http://www.dalidesign.com/hbook/eectest.html

 

When 1st cranked, its normal for the RPMs to run high for about 30 seconds and then settle down, that's normal. For my truck, if take off before it goes through its routine (fast idle 30 sec, then slows down) it'll run rough from then on out until its shut down again. I believe the computer is getting its settings during that time. And its good for the motor warm up and pump some oil around during that time.

 

Thanks for the advice!

I ran the diagnostics check with the instructions from that website. I get a "22" as the hard fault in the engine off test, and "32" as the memory fault. In the engine running test I get a "22".

22 - MAP (vacuum) or BARO signal out of range
32 - EVP (R) EGR not respondign properly during test
EVR (O,R,M) EVP signal is/was low
PFE (R,M) PFE shows low pressure, EGR not seating or memory, not seating intermittently

So what does all this mean and what do I do about it???

Thanks again!!!!

 

>When 1st cranked, its normal for the RPMs to run high for
>about 30 seconds and then settle down, that's normal. For
>my truck, if take off before it goes through its routine
>(fast idle 30 sec, then slows down) it'll run rough from
>then on out until its shut down again. I believe the
>computer is getting its settings during that time. And its
>good for the motor warm up and pump some oil around during
>that time.

My truck is EXACTLY like that.

 

I replaced my MAP when it came up with a code for the MAP. Seems like it was around $25-30. For the EGR, I replaced my too several years ago ($90) along with the EGR sensor. But since then I made the EGR restrictor plate, so for the most part my EGR doesn't run exhaust gas thru my intake. With the plate in place, I do get the EGR code, but from memory, I thought it was code 33, maybe it was 32?

 

HEHE I took the MAP sensor out and checked it (Autozone instructions) and it drops 20 Hz at 15 in of vacuum like it should, so the MAP is not bad. This means I have another problem. I still can find it. One other thing I noticed is that the motor hunts around at idle, it will idle normally then dip just slightly like something is pulling it down.

any advice here???

 

Okay, I chased the same badger myself about a year ago. Turns out my code 22 (MAP) was actually a repeating code 11 closely spaced. Probably the same in your case. Your computer is telling you everything is a-ok as far as it can tell. The other code is in memory, meaning something erred and set this code in the computer sometime in the past. Sometimes a sensor can go out of range long enough to set a code, then correct and get right again. Could be this, or could be the last owner had this problem and replaced the part indicated by the code, BUT DIDNT CLEAR THE CODE. After a repair, you must clear error codes by pulling the battery cables for about 30 minutes. Just like resettting or rebooting your computer at home or work. Try that first. If the problem persists, check the EGR code by unplugging the vacuum line at the EGR valve and plugging the hose. If it runs better, you need an EGR valve. If it ain't the EGR valve, could be the IAC, idle air control, valve that controls idle speed and quality. The IAC looks like a cigar tube with a black two wire electrical connector on one end. It sits right next to your intake air tubes that run from the air filter box with to the plenum. If you unplug that electrical connector while the truck is running, it should die. If not, then you should clean or replace your IAC. You can clean it with carb cleaner and some fine brushes...very easy to take apart and put back together. If any of this fixes your idle problem, but it still starts hard when hot, check your red battery cable. If its stock, replace with a bigger gauge cable. IE. yours is probably 8 guage...so go to 6 or 4 gauge. You can get these at most parts stores. Heat causes increased resistance in electrical cables, so an old, corroded cable can cause hard starting when its hot. Good luck. Let us know how you fare.

 

well I continue to be stumped. Tomorrow I will block the vacuum line to the EGR before going to work. The thing that gets me is that the motor only wants to start when it has been sitting for a long time (overnight) or after it had been run in the last hour or so. I am thinking that the IAT sensor may be bad because it starts good when it is cooler (sometimes). My MAP sensor is OK and the TPS sensor seems to be ok. I'm starting to think she might have a cracked intake EEK!!!!

 

I ran into the same problem with my 86.
It gradually got harder to start. If the engine was
hot on a hot day, I'd have to grind the starter to death
and the engine would fire on a few cylinders and quit
many times before finally running properly. Also
the truck was very low on power. It seemed that the
problem crept up on me so slowly that I didn't notice
the loss of power. Then when I finally figured it out
and fixed it, was like getting a new truck to have all
the power I had forgotten about.
I went through many of the same attempts to fix it you
describe, but finally the fix turned out to be the
ignition module. I thought it was kinda puzzling since
normally I expected the power module to either work or
completely fail, but as I found out, they can get weak too.

 

I just had my '89 f150 die because of a bad ignition module. That could very well be your problem seeing as I was having some of the issues you describe before I put the new module in. The thermal transfer grease between the module and the base of the distributor is key. The module is VERY sensitive to heat, and a uniform and complete covering of grease on the mating surfaces is key to sinking heat from the module to the engine.

Take your module off and have it tested at autozone or someplace, it's worth a try.

Good luck!