96 3500 6.5 hesitating and surging

[HANK1948]

my truck when I start it in then morning and drive off it hesitates and surges at part throttle but if I put the pedal to the floor it runs fine, but also after it warms up it does not do it at all :confused:

[HANK1948]

could it be a PMD?

[tom.mcinerney]

Hank-if surging, good chance the onboard diagnostics have set a 'code'. If scan for the code, that could narrow down search.
Typically the FSD/PMD acts up when hot, better when cold.
A worn liftpump/OPS might cause falter right after start. Have bled filter of air, drained water, checked pressure?
Might read threads with similar problems if do 'search' above; input symptoms.

[HANK1948]

tom mac, the SES light has never lit up , the filter was changed a month ago, also if it had air in the system wouldnt it surge if its cold or warm?

[toyboxrv]

I had a similar problem recently with my 94. Only occurs when cold and at hard throttle it would run fine. Eventually quit going down the freeway and I had codes of 35, 36 and 98. I replaced the pump and the surging quit but a 1000 miles later stalled again. Had a 35 again but no 98, a cylinder fault code. Replaced the FSD which I had reused on my remote mounted cooler on the new pump. Now I have no stalling, no codes and no surging.

[Barry Nave]

Toy
I had all the same codes and more , know what?
Replaced the crank pick up and all is great :D
Our pumps seem to be the frist to R&R only to see the ones that have trouble,then after R&R the pump still have trouble :confused:

[toyboxrv]

I got the 98 code twice, once after the fisrt time it quit, cleared it and then it occured again. I haven't seen it since changing the pump and I have no surging either. Since my original pump had 172k on it, I wasn't willing to take a chance that it would leave me stranded and I had a backup available. May not have been the pump, but it runs fine for now.

[BUZZ]

MY 94 does exactly the same thing only I get 35, 36.
I am picking up a crank sensor and give a whirl. It's only a hall effect so should be less than $100.00 I hope.
Buzz

[tom.mcinerney]

Hank- I was just thinking that a little air got into fuel when idle/cold [dried/loose filter canister oring, dried/cracked hoses, worn injector pump shaft seal]; while system warmed up it bled air, then all components seal...

[Jim H.]

BUZZ - So I'm not the only one thinking this may be a timing problem. I have a similar problem with my 99, sometimes smokes a lot on startup and misses/surges, sometimes it doesn't. The fact that it was intermittent makes me think it is electronics. The problem did get better when I put in relays to power the electronics but still happens sometimes. I bought a crankshaft position sensor but have not had a chance to put in yet. After I get it in I will get it timed. If the voltage to the computer was low, the timing may be off. The price for the sensor was $63 or so. I don't know if these Hall Probes wear out but the ones on our mass spectrometers do.

[BUZZ]

Jim,
My experience with hall effects is that they can start to go intermittent, but usually related to increase in temp. It does stand to reason that if cold, they could become lazy. Typically they just fail. It does look to be a 3 wire sensor which indicates that it is a sink type Halll effect. IT has a magnet built in to the sensor and as a ferrous metal passes by the hall it sinks away the magnetic lines of flux and creates the pulse. Weak magnet over time, cold enviroment for the silica I guess it could cause some strange things. $63 bucks, I am gettting one this week.
Buzz

[HANK1948]

you guys say you are changing the pump ,you mean lift pump or injection?

[BUZZ]

Hank,
The pump reference is probably to Injection due to worn seals and such allowing air to enter the system. I don't believe that is the cold start problem, as too many folks have this issue with fairly new pumps. I have a new crank position sensor that I will install over the weekend, hoping to improve cold starts. Before I would spring for a new IP, unless under warranty, I would install clear fuel hose and look for air bubbles in the return line. If you have air in this line you have fuel hoses, filter housing or IP that is allowing air into the system.

Related to lift pump, make sure it is operating and pumping fuel, if not oil pressure switch could be at fault.
Buzz

[BUZZ]

Bought a crank sensor, $48.00 bucks, installed last night. Not cold enough right now but next week will tell if any difference.
Seems not to be so lazy starting though
Buzz

[Jim H.]

I put the new CPS in this morning. It seems smoother and more responsive but that may be wishful thinking. Will see how it starts tomorrow. Getting the timing set next week, that may make a difference also.