Openai/69191494-216c-8006-993a-611af9e39192

This conversation was exported from ChatGPT

gpt-5-1

User: Really need some help here guys.

Really need some help here guys. I have an M1097A2 with 6.5non turbo that while driving lost power and started smoking. At the advise of several I pulled the IPand had it rebuilt. While waiting for it to get back, I replaced the fuel filter, all fuel lines, CDR valve, and lift pump, starts great and idles smooth but still no power and still smokes like hell. I seen several in here that have had the same issue but nobody has posted a fix. Is there one? Thanks in advance

Assistant: Here’s the straight talk on 6.5 NA Humvees M1097A2 and what usually causes exactly what you’re describing — good start,…

Here’s the straight talk on 6.5 NA Humvees (M1097A2) and what usually causes exactly what you’re describing — good start, smooth idle, but no power under load + heavy smoke even after a fresh IP, lift pump, lines, filter, and CDR.

This pattern almost always comes from one of these four things:

✅ 1. Injection Pump Timing Is Off (MOST COMMON)

On the 6.5 NA, if the IP is off even a hair, you get:

• Low power
• Lots of black or gray smoke
• Good idle but falls on its face when you give it throttle

Even shops sometimes reinstall them a tooth off.

Check:

• Make sure the timing marks on the pump and timing cover are aligned.
• If marks are aligned and it still smokes, loosen the IP and rotate it slightly toward the driver’s side (advances timing).
• Small adjustments make a HUGE difference.

If timing is retarded, you get precisely the symptoms you're seeing.

✅ 2. Air Intake Restriction / Stuck Air Filter Door

HMMWV air filter housings have a vacuum-restriction safety door. If it sticks shut → engine can idle but can’t breathe → smokes like a freight train.

Check:

• Remove the ducting to the air filter.
• Start it and rev it gently.
• If smoke clears and power returns → found your issue.

✅ 3. Crushed, Kinked, or Collapsed Return Line

A blocked return line = IP over-fuels = heavy smoke + no power.

Check:

• Make sure return line from the IP to the tank is flowing freely.
• These rubber sections can collapse internally even when they look normal.

✅ 4. Timing Chain Stretch

6.2/6.5 engines with miles on them can jump a tooth or stretch the chain enough to retard cam timing.

Symptoms:

• Good idle
• Terrible power
• Thick black/gray smoke
• Won’t rev cleanly

If your chain has 20–30 years on it, it’s suspicious.

Secondary Possibilities (but less likely since you rebuilt IP + replaced lift pump):

• Stuck open injectors

Even one injector stuck open = white/gray smoke + low power.

• Low compression

But this usually gives hard starts — you said it starts great, so unlikely.

• Collapsed intake hose

They can suck shut under throttle.

• Blocked muffler (if not military exhaust)

Civvy conversions sometimes plug internally.

🔧 Strong Recommendation: Do This Simple Test

This will tell you QUICKLY whether it's timing or fuel delivery:

Test 1 — Crack an injector line while idling

If one cylinder isn’t contributing, the smoke will change when you crack its line.

If nothing changes, you might have a dead injector.

Test 2 — Try advancing the IP a tiny bit

1. Loosen the three IP nuts slightly
2. Rotate pump toward driver’s side ~1–2 mm
3. Tighten and test

If it suddenly gains power and loses smoke → your timing was retarded.

This is the most common actual fix people forget to report back on.

👉 The fix you’re looking for (based on pattern)

90% chance: your injection pump timing is retarded by just a hair.

This exact problem shows up in HMMWV groups weekly after IP replacement.

If you want, tell me:

• Color of smoke (black, white, blue?)
• Does it rev freely in neutral?
• Does the smoke change when you floor it?
• Does it have the original KDS or Stanadyne IP?
• Any unusual noises?

I can tell you exactly which system is failing.