VCCA Home Forums GENERAL DISCUSSION New User Forum 1989 C3500 Idles fine...but dies in gear-Help!!!

My 1989 C3500 7.4L keeps dying on me...It starts fine, idles in park and neutral fine, but when you put it in gear it dies (R or D)...I replaced the MAP sensor, oxygen sensor, EGR valve, IAC valve. Runs fine once it gets going...TBI seems to be getting plenty of fuel...perhaps an oxygen problem? It started out as an intermitent problem but now is doing it more often. Had a mechanic put it on a machine but couldnt get a code to come up. Any ideas?

Look at spark plugs and leads. I would be suspicious of the leads if the measure more than 11k ohms. The set going bad at the same time is not very common but may have been dropping out over a period.
Tony

Sorry to take so long to reply... someone suggested an idle actuator but it does not have an idle actuator on the TBI....we just put a rebuild kit into the TBI...it definitely needed it, bad o-rings and gaskets...unfortunately truck is still acting up. Last mechanic to look at it ran all kinds of tests, couldnt find any vaccum leaks, fuel pressure is good, replaced O2 sensor, EGR valve, IAC is good, MAP sensor is good, idle count is opposite of what it should be...higher in park/neutral and then drops when you put it in gear...even replaced ECM/PCM thinking it was a bad computer...still stalls on me. Mechanic says it acts like it has a vaccuum leak...but none to be found. Someone suggested that it could be a bad distributor...to disconnect set timing plug and if it runs then to replace distributor shaft and pickup coil, havent tried this yet though...mechanic did test ignition module and it was good... I am just baffled as to what could be the problem??? Any ideas????

i had a similar problem with my 94 454. it was the distributor shaft . the top plate (with the 8 triangles stamped into the plate) was rotating on the shaft itself. the truck was only 6 months old when it happened. good luck with your big block.mike

When you rebuilt the TBI did you make sure the vacuum ports where clean. I have seen the one that goes to the MAP sensor restricted and cause the MAP sensor to be slow to react, would be like a bad accelerator pump. Also a weak magnet in the pole piece in the distributor may cause it. When they checked fuel pressure did they also do a volume test and a dead head pressure test? Also I would check the ECM grounds and they should be on a thermostat housing stud and also may be one on a bolt going in the back of the head.