flashZR1/Z06

90 ZR1 running rich, fouling plugs on passenger side then oxygen sensors - worse on passenger side. heavy carbon fouling. Possible causes?

A26B

1. Remove vacuum line from Fuel Pressure Regulator. Key on. Any fuel coming from vacuum nipple on Regulator?
2. Are all 4 plugs on passenger side fouled? If not, which ones are fouled?
3. Are plugs oily?
4. Are the stock exhaust manifolds & cats still in place?

Dominic Sorresso

billschroeder5842

Jerry is the authority but let me make a guess-- and it IS a guess. If your FPR was faulty (ripped membrane) raw, un regulated (or at least less regulated) fuel would get dumped into the system. The first (or actually top) feeder hose for the fuel rails feeds the right side. Hence any fault in the FPR would show up on the right side of the engine as extra fuel dump.

Am I close?

Dominic Sorresso

You would need to ask Jerry, but its still unclear to me why it would discriminate that way.

A26B

Originally Posted by A26B
Ruptured diaphram in the Fuel Regulator would dump fuel back into the plenum at the vacuum source, located at L-Rear of plenum, creating a fuel rich condition. Although it wouldn't be bank specific, I suggested this check to easily eliminate a possible source of excess fuel.

A weak/bad O2 sensor would control fuel to the entire bank. I asked this question to determine the probability of the enrichment being related to the O2 Sensor. If less than all plugs fuel fouled, then probability of bad injectors is greater than bad O2 sensor.

OP states plugs are fouled due to a rich fuel condition, but does not offer any information to support fuel over oil. If plugs are oily then other problems may exist. Added to the results of question #2 helps to determine other possible sources of the plug fouling.

If it turns out the plugs are oil fouled, and considering only one bank is affected, the possibility catalytic reversion comes into play, depending on whether the exhaust manifold & cats are still on the engine. Although 90~92 models have the same manifold/cat design, 1990 models seem to have a higher incidence of catalytic reversion. Reversion of catalyst dust is like a coarse lapping compound and literally wipes the oil ring scraper lands completely from the oil ring.

A bad O2 sensor may be at fault, but without the means to test it and no DTC codes given, it's hard to consider it as being the primary source. Insofar as the problem being injector related, it would be unlikely that all bad injectors are on the right bank only. As such, the simple, no cost checks offered can help with the diagnosis.

Dominic Sorresso

flashZR1/Z06

Fouling passenger side plugs and oxygen sensor. Need to check for. Modified with headers, 3" cars & 3" exhaust.