help!part deux

[mooneyes 89]

still trying to perform computer exorcism-have checked vacuum,checked timing,replaced$$$$$$$$$$$$ensors,still won't idle without me applying throttle featherfoot style,hesitates badly when throttle given,and backfires!when i finally chug it up to higher rpm,the engine runs pretty smooth-no smoke,no strange noises!i gotta believe internally,she is fine-it's just some sensor or something gone nuts!hoping to find someone on here who has had similar probs!i have much experience with old-school carbureted motors,but this is like voodoo to me!anybody out there who can help?

[Sparky2263]

What was the vacuum reading at idle, fully warmed up? Also, what timing spec did you set it to and what procedure did you use?

Hisitation and backfire is indicative of a very lean mixture or retarded timing.

[mooneyes 89]

well-it took forever to get it to idle right,but when it did-it was between 18 and 22 hg on the gauge(vacuum)as far as timing-i only checked mechanical timing(relation between cam and crank)because i thought maybe it had jumped teeth on cam gear.this doesn't seem to be the case,however!this was grandpa's truck,meticulously maintained forever!running fine one day,then the next day-it's like this!it has to be ecm,bad connection,etc!i have a factory service manual-i have used the info provided there,but am reaching no means to an end!for two weeks now i have been beating my head against the wall!maybe i just need to bite the bullet and have it towed to a mechanic!(spread cheeks wide!)was hoping that someone could give me some direction to go in-codes 33 and 34 indicate vacuum probs-but i can't find any!thanks for the reply!

[bosco_108]

Make sur you check the vacuum, compression(to check engine internally), fuel flow, the carb itself and your timing. One thing might make act funny, but would you go to the doctor for a checkup if you needed surgury? Make sure you check everything. From simplest to the hardest. Peace

[Sparky2263]

Code 33 is MAP sensor voltage high (low vacuum) and code 34 is MAP sensor voltage low. Make sure you have manifold vacuum getting to the MAP sensor. If you don't, it'll run like crap.

To accurately ck. the timing, you need a timing light. You disconnect the EST connector then adjust the timing.

First, fix the MAP sensor codes. Also, is it a 2.8 or 4.3?

[mooneyes 89]

it is a 4.3,and that is where i read vacuum from-the hose that goes to the map sensor.it's will be hard if not impossible to read timing with a timing light,because i can't keep it running without teasing the throttle-it won't steady idle!thanks for the input!low vacuum doesn't seem to be my problem,but the computer thinks it is!i will try to get my son to juke the throttle long enough for me to read timing,and see what happens today.