Strange Problem; Quantum 1.6TD

[Uriah T.]

Just had the head and camshaft repaired/rebuilt on my Quantum (timing belt jumped), and now it's experiencing a strange issue.

The timing is correct, the injection pump seems to work fine, and is timed correctly.  What occurs is that the car starts and runs fine for a few seconds, then seems to lose power.  Turbo is working well, kicks in correctly- but its at lower revs that the inexplicable power loss occurs.  Checked the timing, injection pump, injectors, all seems to be working well.  Any ideas about this issue?

Thanks for any and all ideas-

[Quantum TD]

Hmm. Mildly sketchy.

When you say you had the head rebuilt/repaired: exactly what was done?  Like any head job, there are levels of head repair quality/knowledge.

Because there is little resale value in the older 1.6 diesels (sorry to admit it guys), and even less common knowledge about them among machinists (they're a dying breed), many shops treat the early 1.6 diesel head like a Chevy 350 iron head: mop and glow/ go.

Unfortunately, there aren't many shops that intimately know these older heads, and they'll often do a quick and dirty job on them, because a) the owner wants it that way, b) they think thats what the owner wants, or c) they haven't got the  experience to work them properly given the goofy nickel pre-chamber insert/pucks, etc.

So, there are many potential problems here. But 1st, you need to enlighten us on exactly what was done to the head, and how long the car was apart, how log you've had the car, mileage, etc. The more info, the better. These factors willl help us to help you.

Superficially, it sounds like compression loss. If the IP was fine before, then this is not a fuel problem (unless the car sat for a long time). The turbo sounds good (as you claim), so the turbo is ruled out (does the turbine spin freely I assume?). Then there's the Blow Off valve (BOV) These came on tjje Quantum, but not other cars of the same vintage. You could always disconnect it if you think that there is a problem (but if you're planning on driving it for a while, you should troubleshoot the BOV 1st).  So, if the IP, the turbo (and components) check out, as does the timing, then you need to look to the head work .

Did you use new headbolts or re-use the old ones. If you've re-used the headbolts, then you're f-ed bobby.  New gasket I hope?  If you've done all that, then it's time to question the headwork.

Any asshat cans swap in some new valves to replace some  bent ones. A REAL mashinist will do the following: replace ALL of the  valve guides (these 1.6 diesel engines eat guides), replace ALL of the exhaust valves (again, these heads eat exhaust valves by pitting the shafts), recut  and reces the valves (if the head was machined, then the valves should be reecessed). If the head was warped/damaged, then the head should have been resurfaced. After which point, the valves should have been recessed to the proper depth/projection. If that all was done, then the camshaft journals should have been checked for trueness. If the journals were true, then the camshaft itself should have been checked for trueness.

I guess the bottom line is that:
1) If the IP is good, then it's not a fuel problem
2) if the timing is right, then it's not a mechanical problem
3) If you were trying to cut corners on the head work, it may be showing up now.
4) If you have not set the cam and injection pump timing, you should check that first.

If none of the above has been done, then it's time for reevaluation. Please let us all know what has been done

Good Luck

[Zulfiqar]

by your statement, sounds like the valve stems are an mm short or something.

[jtanguay]

any bubbles in the fuel line at idle?

[Uriah T.]

Thank you all for the suggestions.

Unfortunately, I can't answer most of the questions here- my mechanic (a well known LA VW repair shop) had the head rebuilt, and cam redone.  But he's hit a roadblock as to what this new problem might be.

I'll see if I can get these suggestions to him, as he's the person who has done all the timing checks and oversaw the top end rebuild.

What I know:
The mileage on the car is around 150k- before this happened, the only thing really wrong was that the a/c didn't blow cold.
The timing jumped, and the head was repaired and put back on within a 1-2mo time span, with the proper 3-hole gasket.
The pump and turbo seemed to be working fine before.
The reason the timing jumped initially is that the gear on the cam was stripped, and kept sliding the timing belt.
He has checked the cam and pump timing.

I hope the guy didn't cut corners, because the fact is: I told him I wanted it back on the road as a reliable vehicle.  I know I'm not going to get out of this car (resale) what I put in, but a good mpg wagon sounds good to me.  I paid a pretty penny for the car, since I am in Southern California, where diesels go for more than anywhere else (except Central America!).  Didn't have much blowby when I got it, and it spooled up well.