Hi, all. Checklist below. The RPMs often dip down to ~500 or so when any load is applied while idling or cruising with no acceleration (braking at idle or while coming to a stop, shifting into gear). It threatens to stall but doesn’t; the dip is followed by a momentary surge. When that’s not happening, it handles loads fine and idles at about 700-800. I’ve also had some harder warm/hot starts, but that’s not always a problem, and I haven’t gotten stranded yet; cold start is fine. The RPM dip was happening before I blew a head gasket and refreshed the engine about 500 mi ago.
New or reman parts during the refresh: rod & main bearings, heads, DS4, injectors, fuel sender, EP158 lift pump, glow plugs, PMD, OPS with extension hose, et al. I timed the pump and did a TDCO relearn: everything’s within spec. Anyone have a similar dip-surge problem?
Problem: Explain your problem in concise language (ie: Cranks but won’t fire). ___RPMs often dip to ~500 and then momentarily surge – doesn’t stall; warm/hot starts are often harder
Demographics: tell us about your truck and your ambient conditions: ___rural northwest PA, cold-ish winters, warm summers
- Year: ___1997
- Truck model and class (ie: c2500) ___Suburban K2500
- Automatic or Standard ___Auto
- Mileage: (indicate miles or km) ___347K mi (257K mi on factory replaced engine, 500 mi on refreshed engine)
- Replaced parts and mods (IP, PMD, chip/PCM, TM, injectors etc)___new relocated PMD, reman DS4, injectors, main & rod bearings, heads, starter, fuel sender, AC Delco EP158 lift pump, mechanical turbo waste gate controller, manual glow plug switch, et al.
- Model: ‘S’ or ‘F’ engine, NA or Turbo, EGR? ___F VIN, turbo, no EGR
- Ambient outside temp: (indicate *C or *F) ___avg 70’s lately
- What fuel are you using? (#1 Diesel, #2 Diesel, Bio, VO, WVO, etc) ___#2
- What fuel additives are you using? ___Opti-Lube
- Where are you located? ___NW PA
General maintenance: inspect and evaluate the condition of each. When were they last changed?
- Air filter ___500 mi
- Fuel filter ____500 mi
- CDR Valve? _____1 mi
- Coolant – last flushed/replaced at _______500 mi
- Oil – synthetic/regular, changed at ______400 mi
- Batteries – state of charge, (matched set) replaced at ____12.6V, 1000 mi
- Battery cables and grounds (removed, cleaned and tightened): ____500 mi
- Glow Plugs - how many miles on them? ___500 mi What type? ____Bosch Duraterm
- Injectors - last changed at ____500 mi
History: (Describe how the problem first appeared.)
- What were you doing when it happened? _____normal driving
- How was the truck running fine before this problem appeared? ____fine
- Has this problem ever happened before? _____Y
- Describe any related factors that might be part of the problem. _____See end of checklist
- Have you checked for DTC (Diagnostic Trouble Codes)? ___no DTCs
1] Starting:
1a] Does the engine start? ___Y
1b] Does the engine crank over? ___Y
1c] Are your batteries fully charged? ___Y
1d] Have you removed, cleaned, and tightened all battery connections? ___Y
1e] Does your Wait to Start light come on for a time? How long? __several seconds, then flashes several more
1f] Does your glow plug light come on? __NA For how long? ____NA
1g] Do you see smoke from the exhaust while cranking? What color? __N
1h] Does the Service Engine Light Glow during Start/bulb check? ___CEL always on since vac pump delete
2] Fuel Issues (if not running): VEHICLE RUNS, BUT I’LL ANSWER ANYWAY
2a] Can you hear your lift pump working? ___Y
2b] Do you get a steady flow of fuel from the water drain (T-handle) ? ___Y, >10 psi engine off, 9.5 psi engine idling
2c] Loosen the inlet line from the IP – is fuel coming out (Lift Pump on)? ___Y
2d] Loosen an injector line and crank the engine - does fuel come out? ___Y
2e] Do you hear a vacuum (hiss) when you remove the fuel cap? __Y
3] PMD / IP Issues
3a] Location of PMD (on pump, on intake, remote mounted) ___remote (bumper)
3b] Condition of Extension harness (if used) Vendor or Homemade? __vendoer
3c] Condition of grounds / ground wires to IP / PMD. Check Harness. __good, clean
3d] PMD Make: __Flight Systems
3e] PMD Age: ___2021, just installed
4] Stalling Issues
4a] Do you experience stalling only when hot? ___N
4b] Does it stall under particular circumstances? (ie hit bump, or on accel) ___N
4c] Does pouring cool water over the IP seem to help with restarting? ___NA
4d] Is stalling momentary (engine recovers)? ___NA
4e] Does SES light come on when engine hiccups? ____always on
4f] Does cruise control quit working when engine hiccups? ____don’t know
4g] Does re-starting seem to reset engine, restoring cruise and power? ___NA
4h] Changes to dash lights or instruments during stalling events? ___NA
5] Running Issues
5a] On cold start, does upper rad hose get hard before engine warms up? __N
5b] Any bubbles or oil film in coolant overflow tank? ___N
5c] Any white slime on oil surfaces (dipstick, CDR, oil Fill cap)? ___N
5d] Excessive white smoke from exhaust on cold start? ___N
5e] Excessive black smoke from exhaust under hard acceleration? ___N
6] Performance Issues
6a] Do you have gauges (boost, EGT) ? ___boost
6b] Maximum boost under load? ____~10 psi
6c] Have you added a performance PCM (reflash) or Chip? ___N
6d] Have you changed exhaust / downpipe / crossover? ___N
6e] Wastegate – mechanical or vacuum (OEM)? __mechanical
7] Temperature-related Issues:
7a] Single or dual thermostats? ___dual
7b] Have you replaced them lately? Manufacturer of replacements? __500 mi
7c] Have you pulled and cleaned Radiator and coolers lately? ___500 mi
7d] Have you replaced the fan clutch? Manufacturer of replacement? ___N
7e] (winter) Have you tested your antifreeze? Good to what temp? ___N
7f] (winter) Are you using a winter grille cover? ____N
New or reman parts during the refresh: rod & main bearings, heads, DS4, injectors, fuel sender, EP158 lift pump, glow plugs, PMD, OPS with extension hose, et al. I timed the pump and did a TDCO relearn: everything’s within spec. Anyone have a similar dip-surge problem?
Problem: Explain your problem in concise language (ie: Cranks but won’t fire). ___RPMs often dip to ~500 and then momentarily surge – doesn’t stall; warm/hot starts are often harder
Demographics: tell us about your truck and your ambient conditions: ___rural northwest PA, cold-ish winters, warm summers
- Year: ___1997
- Truck model and class (ie: c2500) ___Suburban K2500
- Automatic or Standard ___Auto
- Mileage: (indicate miles or km) ___347K mi (257K mi on factory replaced engine, 500 mi on refreshed engine)
- Replaced parts and mods (IP, PMD, chip/PCM, TM, injectors etc)___new relocated PMD, reman DS4, injectors, main & rod bearings, heads, starter, fuel sender, AC Delco EP158 lift pump, mechanical turbo waste gate controller, manual glow plug switch, et al.
- Model: ‘S’ or ‘F’ engine, NA or Turbo, EGR? ___F VIN, turbo, no EGR
- Ambient outside temp: (indicate *C or *F) ___avg 70’s lately
- What fuel are you using? (#1 Diesel, #2 Diesel, Bio, VO, WVO, etc) ___#2
- What fuel additives are you using? ___Opti-Lube
- Where are you located? ___NW PA
General maintenance: inspect and evaluate the condition of each. When were they last changed?
- Air filter ___500 mi
- Fuel filter ____500 mi
- CDR Valve? _____1 mi
- Coolant – last flushed/replaced at _______500 mi
- Oil – synthetic/regular, changed at ______400 mi
- Batteries – state of charge, (matched set) replaced at ____12.6V, 1000 mi
- Battery cables and grounds (removed, cleaned and tightened): ____500 mi
- Glow Plugs - how many miles on them? ___500 mi What type? ____Bosch Duraterm
- Injectors - last changed at ____500 mi
History: (Describe how the problem first appeared.)
- What were you doing when it happened? _____normal driving
- How was the truck running fine before this problem appeared? ____fine
- Has this problem ever happened before? _____Y
- Describe any related factors that might be part of the problem. _____See end of checklist
- Have you checked for DTC (Diagnostic Trouble Codes)? ___no DTCs
1] Starting:
1a] Does the engine start? ___Y
1b] Does the engine crank over? ___Y
1c] Are your batteries fully charged? ___Y
1d] Have you removed, cleaned, and tightened all battery connections? ___Y
1e] Does your Wait to Start light come on for a time? How long? __several seconds, then flashes several more
1f] Does your glow plug light come on? __NA For how long? ____NA
1g] Do you see smoke from the exhaust while cranking? What color? __N
1h] Does the Service Engine Light Glow during Start/bulb check? ___CEL always on since vac pump delete
2] Fuel Issues (if not running): VEHICLE RUNS, BUT I’LL ANSWER ANYWAY
2a] Can you hear your lift pump working? ___Y
2b] Do you get a steady flow of fuel from the water drain (T-handle) ? ___Y, >10 psi engine off, 9.5 psi engine idling
2c] Loosen the inlet line from the IP – is fuel coming out (Lift Pump on)? ___Y
2d] Loosen an injector line and crank the engine - does fuel come out? ___Y
2e] Do you hear a vacuum (hiss) when you remove the fuel cap? __Y
3] PMD / IP Issues
3a] Location of PMD (on pump, on intake, remote mounted) ___remote (bumper)
3b] Condition of Extension harness (if used) Vendor or Homemade? __vendoer
3c] Condition of grounds / ground wires to IP / PMD. Check Harness. __good, clean
3d] PMD Make: __Flight Systems
3e] PMD Age: ___2021, just installed
4] Stalling Issues
4a] Do you experience stalling only when hot? ___N
4b] Does it stall under particular circumstances? (ie hit bump, or on accel) ___N
4c] Does pouring cool water over the IP seem to help with restarting? ___NA
4d] Is stalling momentary (engine recovers)? ___NA
4e] Does SES light come on when engine hiccups? ____always on
4f] Does cruise control quit working when engine hiccups? ____don’t know
4g] Does re-starting seem to reset engine, restoring cruise and power? ___NA
4h] Changes to dash lights or instruments during stalling events? ___NA
5] Running Issues
5a] On cold start, does upper rad hose get hard before engine warms up? __N
5b] Any bubbles or oil film in coolant overflow tank? ___N
5c] Any white slime on oil surfaces (dipstick, CDR, oil Fill cap)? ___N
5d] Excessive white smoke from exhaust on cold start? ___N
5e] Excessive black smoke from exhaust under hard acceleration? ___N
6] Performance Issues
6a] Do you have gauges (boost, EGT) ? ___boost
6b] Maximum boost under load? ____~10 psi
6c] Have you added a performance PCM (reflash) or Chip? ___N
6d] Have you changed exhaust / downpipe / crossover? ___N
6e] Wastegate – mechanical or vacuum (OEM)? __mechanical
7] Temperature-related Issues:
7a] Single or dual thermostats? ___dual
7b] Have you replaced them lately? Manufacturer of replacements? __500 mi
7c] Have you pulled and cleaned Radiator and coolers lately? ___500 mi
7d] Have you replaced the fan clutch? Manufacturer of replacement? ___N
7e] (winter) Have you tested your antifreeze? Good to what temp? ___N
7f] (winter) Are you using a winter grille cover? ____N