In need of some advice-power problem.

[channingd]

O.k. I have a 1987 SWB with the 350 TBI. It idled ruff so first thought was a vacuum leak. Found one of the tubes coming off the TB to the emissions undone. Plugged it back in and idles nice. Good.

But, when I give the truck full throttle, it boggs down and hesitates for awhile and then recovers. Also, it will at times at stop lights or coming to a stop, just die. Starts right back up, but what an embarrassment. I thought timing. Still have not checked it, but I thought I would also clean the injectors and housing with some cleaner. Noticed that the Map sensor vacuum line was sealed with a bolt in it and the Map sensor was plugged in with the three wire plug but nothing on the vacuum nipple. Plugged it back up and the truck will not hold an idle, dies when put in gear, and just won't run. Bad Map sensor(?). Read on here for an hour and all pointed to a bad Map so I went and bought a new one. Plugged in the new one and same symptoms. Unhook the vacuum line to the Map and plug it, truck is back to running although still not great.

I got this truck 4 years ago and never did anything to it. 4 months of body work, new interior, new transmission, new paint, and new wheels and tires, the only thing left is the motor.

Any ideas? Thanks, Channing

[powerdriver 1958]

Just a thought,company trucks that i worked on had a bad habit of the base gasket going bad.The one between the tbi body and the manifold.looked like it had tried to suck it in the motor.............Never set a code when that happened either.

[channingd]

Powerdriver,

Would that make the Map system not work?

[Captkaos]

Is it throwing any codes? What are they. Just put a paper clip in the A and B terminals of the ALDL, turn the switch on and count the number of flashes. The first one is always 12.

[channingd]

Originally Posted by Captkaos

Is it throwing any codes? What are they. Just put a paper clip in the A and B terminals of the ALDL, turn the switch on and count the number of flashes. The first one is always 12.

Well,

I took it over to Affordable Automotive which is 1 blk from work. They have worked on all our work and personal vehicles and are honest and professional. The owner called me an hour later and said he couldn't do anything for me because they couldn't even get the trucks computer to talk to theirs. So, to answer the code question-I don't know.

[Captkaos]

Try what I posted. If you don't get any flashes, check the bulb.

[channingd]

Man I hate to sound stupid, but I don't even see a Check Engine light. I have a fasten seat belt and park brake lights with the fuel gauge but that's it.

I'm sure there's supposed to be one but?

[channingd]

Wow! I've been reading a lot of posts and have to say that my truck is probably screwed. Bad HV coils, possibly, spark plug wires, timing, spark plugs. Too much reading tonight.

[channingd]

Update:

This morning in Albuquerque it was 27 degrees. My truck started good. It always takes a few cranks when it's cold. Fires up immediately if it has been less than 10 minutes of shut off time. (Possible leaking injectors? That just came to me as I was typing this.) Anyway, the truck seemed to run fine til I got into traffic and it died. Started right back up but wanted to keep dying. When I would give it gas it would sputter and want to die. Acting like when I had the vacuum line hooked up to the Map sensor.

I took it home, about 10 blocks, and it seemed to run better by the time I got there. I just pulled the other car out and took it to work today. Don't want to be stranded in 27 degree weather.

[Damien]

I'm just going through my thought process here, so bear with me.

With the map sensor unhooked you are running in open loop.

On multi port stuff, like the 3.8 or 3.1, a leaking fuel pressure regulator will cause the engine to crank a few times on a cold start. When the engine has been shut off for a short time and restarted, it starts fine, BUT it does not generally cause driveability problems.

I keep thinking it could be related to low fuel pressure or a plugged fuel filter, but the map makes me think that it is not the fuel pump. Have you done a tune up at all? ie fuel filter, plugs, wires, cap, rotor.

The vacuum lines are plastic and can brake easy. Are those OK.

I'm pretty sure the map is used to measure the load on the engine. The signal from the map will adjust the timing based on engine load, so under high load conditions such as acceleration the timing is not adjusting or the ignition system is worn out. (plugs, wire, ect). So, Try a tune up, and test the ignition module and coil.

Can I get someone to second this?

[Captkaos]

the check engine light is in the speedo cluster. It should come on when you turn the key.

Put a timing light on the motor while running and point it at the injectors see if you can tell if they are spraying correctly.

How is the fuel filter, if it is old or unknown, replace it.

You can also clamp off the return line to see if it makes a difference, it would be an indication of a bad pump.

I had one that had these symptoms and I had to rebuild the TBI unit, the regulator spring was broken into pieces and one injector was not pulsing all the time.

[channingd]

This is my next plan of attack.

1. Autozone is 2 minutes away. I will go down there and hook up the programmer to get the codes.

2. I have mentioned that everything,body and interior wise is new, so I am going to put a rebuilt throttle body on for good measure.

3. New fuel filter, change all vacuum lines, new air filter, and a new temp sensor.

Then I'll hook up the Map sensor again and see if it will run with that hooked up.

My friends at work are trying to get me to just put a Quadrajet on it and unhook all the computer stuff.

[Captkaos]

Swapping to a Q-jet would be going backwards and you would loose all the benefits of EFI. TBI's are not that complicated, just fix what is wrong and go from there.

You can rebuild the Throttle body for cheap, they aren't hard to do.

[channingd]

That's was my argument in the whole quadajet discussion. I've had carbs and they just seem to be a pain sometimes. Fuel injection is reliable. I didn't think about rebuilding my thottle body myself but I'm sure I can. Do you replace the injectors or rebuild them as well?

[joe231]

Check your EGR valve for carbon build up.
Also check you IAC valve. It could be stuck or not working.

[Damien]

If the injectors are working and not dripping fuel they are probably ok. TBI a a great system for what it was designed for and it is simple if something goes wrong. I would keep the TBI.

[channingd]

Update as of Friday afternoon:

replaced temp sensor
replaced throttle position sensor
replaced various vacuum hoses

checked timing in accordance with the VECI lable. O degrees with the brown/black wire disconnected.

checked the injectors with the timing light as suggested by CAPTKAOS. Both have fuel but not really a spray, more of a dribble. Might suggest a bad fuel filter or bad fuel pump.(?)

I have a new fuel filter I am going to put on and then I'll clamp the return line shut and check the pump.

No symptoms have changed yet.

P.S. I hooked up the vacuum line to the Map sensor again, and again the idle went bad and was loping severe. I then unhooked the vacuum line again and then I unhooked the wire harness the Map sensor. The idle would change and then recover. I then hooked it back up and again the idle changed but recovered.